Elisabeth C. Miller Library

Gardening Answers Knowledgebase

Search Results for: Rosa | Search the catalog for: Rosa

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American Rose Society Pacific Northwest District

Woodland Park Rose Garden

International Rose Test Garden [in Portland]

Information Resources for Roses

American Rose Society


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Plant Answer Line Question

Keywords: Rosa, Planting time, Planting

When should I plant bare root roses?


The Seattle Rose Society suggests planting in March. The roses should be stored in a cool dark place if they cannot be planted right away.

Other recommendations include soaking the roots before planting (8-12 hours), and trimming off damaged or diseased roots. Try to maintain 3-5 canes per plant, and prune back to 3-5 buds per cane.

Dig a hole wide and deep enough to accommodate the roots. Make a cone-shaped mound of soil in the center of the hole to support the plant. Fill the hole 2/3 full of soil and add water to make a slurry--this gets between the roots. Do not tamp the soil. When the water drains, add more soil and repeat the water fill process until you reach the original soil surface (ground level).

Date 2020-03-28
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Plant Answer Line Question

Keywords: Rosa, Pruning

I would like to know when is the best time of year to prune back (heavily) the roses in my garden. I have read that winter is best, when they are dormant, but I have also read spring is the right time.
Also, with roses that are possibly 20 years old or more, and have very woody stems, is it all right to prune them back to the woody (brown parts)? Or should I not cut back past the green parts?


In the Pacific Northwest, most sources recommend pruning in late fall or early spring. Where to cut depends on the type of roses you have (modern, climbers, shrub, etc.).

The Seattle Rose Society also provides excellent pruning information.

You don't mention what type(s) of roses you are hoping to prune, but the June/July 2011 Organic Gardening article by E.J. Hook, former gardener at the Woodland Park Rose Garden, covers basic pruning techniques for the 5 main types of rose.

Date 2019-10-02
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Plant Answer Line Question

Keywords: Rosa, Plant exchanges and donations

I have several immature rose bushes, including some native Washington roses, that must be removed from my property. Are there any organizations, or individuals, who would be interested in transplanting them to another site?


You might want to check out the Seattle Rose Society website, which has lots of good information about roses.

You could also post your information about the roses, or reply to those seeking rose bushes, on the Pacific Northwest Garden Exchange on Houzz.

Another place that might have an interest in helping to find a new home for your roses is Plant Amnesty.

Date 2019-11-14
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Plant Answer Line Question

Keywords: Rosa, Woody plant cuttings, Woody plant propagation

I am trying to grow roses from cuttings. They are sprouting little leaves but are still under empty soda containers for humidity. When I took a few out of the containers, they promptly shriveled up and died. Should I leave them for another month? I don't want to tug to see if they have roots, as that will disturb them. Do I apply foliar fertilizer?


I have listed a few useful webpages about propagating roses from cuttings below.

To answer your question about leaving them under cover, I think you probably should leave them for at least a brief while, given the very cold weather. I don't think you need to apply foliar fertilizer at this stage. The resources below should offer some additional advice on caring for your cuttings.

John Fisher's book, The Companion to Roses (Salem House Publishers, 1986), says that roses grown from cuttings may take longer to flower than those budded on rootstock, but (if they survive the process) they may live longer and will not sucker. Some roses are easier to propagate from cuttings, such as ramblers and Rosa rugosa, as well as some climbing roses and large-flowered roses.

According to Fisher, cuttings can be taken as early as August. You should choose young shoots with ripened wood that have borne flowers, and lateral shoots rather than leaders. He recommends selecting those shoots growing low on the shady side of the plant, and those with leaf joints that are close together. Make a clean cut just below a leaf joint. The cutting should be about 9 inches long with 2 leaf joints in the top 3 inches. Cut off the tip that has borne the flower and the leaf immediately underneath it. Remove leaves (but not buds) on the lower 2/3 of the cutting, since this is the part that will be planted in the ground. The soil should be a mix of loam and sand mixed down to a depth of about 9 inches, in a pot or V-shaped trench. Before planting the cutting, poke a hole in the soil for it to go into. Moisten the bottom end of the cutting with a cotton ball, and dip it in rooting hormone (or willow water). Put the cutting in the soil and press the soil around it firmly. If you need to protect it from frost, cover it with leaves or sacking during the winter. By summer, it should have formed a root, and should be ready to plant in the fall.

The information below may differ somewhat from these directions, but you may get a general sense of how your methods compare, and whether you want to try any of the methods suggested.

University of California Cooperative Extension
Morrison Gardens
The Southern Garden

Date 2019-08-16
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Plant Answer Line Question

Keywords: Transplanting, Rosa

I have a rose bush in the back yard, under a tree, it seems to be thriving but no one can see it blooming. I want to move it to a more prominent place in our yard. What is the best time of year for transplanting this rose?


Moving your rose out from under the tree is probably a good idea. Roses: 1001 Gardening Questions Answered by the editors of Garden Way Publishing (1989), says that the best time to transplant it to its new location is early spring or late fall. Before moving it, prune it, leaving three to four canes. Prepare the new hole in the ground (and) give it some extra attention after it is planted. This resource says that spring transplanting is preferred, because with warm weather on the way, the rose will have a better chance of starting new growth. When digging up your rose, dig a circular trench one foot away from the crown of the plant, removing the soil around the plant with your shovel. Loosen the root ball, and then take hold of the crown and push it back and forth to loosen it. Then lift it out of the hole. Dig a deep hole in the new location. Add two inches of compost, build a mound of soil, and spread the roots over it. Fill in with topsoil, make a ridge of soil around the base of the plant, and water well. Afterwards, water carefully, neither too much nor too little.

Date 2020-03-12
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Plant Answer Line Question

Keywords: Rosa, Disease-resistant plants, Organic gardening, Climbing plants

My neighbor wants a rose, but it will be planted in an organic garden. It is a sunny warm spot (for Seattle), but I think disease resistance is a must. What is a source for disease resistant roses for our climate? Also, does growing clematis on a climbing rose limit its disease resistance?


The reason that clematis and rose make good companions has to do with the rose providing the structure the clematis needs, and the pairing allowing for interesting combinations of color and shape, rather than one providing disease resistance to the other.

Generally, the most disease-resistant roses are species roses, but there are additional choices.

This article from Oregon State University Extension lists resistant roses and their other qualities (scent, repeat bloom, color).

This article from Washington State University Extension is entitled "Disease-Resistant Roses for the Puget Sound Area."

There are several excellent books on growing roses in our area:

North Coast Roses : For the Maritime Northwest Gardener by Rhonda Massingham Hart (Seattle : Sasquatch Books, c1993)

Jackson & Perkins Beautiful Roses Made Easy : Northwestern Edition by Teri Dunn & Ciscoe Morris. (Nashville, Tenn. : Cool Springs Press, 2004)

Roses for the Pacific Northwest by Christine Allen (Vancouver : Steller Press, 1999)

Roses for Washington and Oregon by Brad Jalbert, Laura Peters (Edmonton : Lone Pine Pub., 2003)

Roses for the Inland Northwest. Washington State University Extension ; [Washington, D.C.] : U.S. Dept. of Agriculture, [2004])

This book is a comprehensive guide to combining clematis and roses: The Rose and the Clematis As Good Companions by John Howells ; photographs by the author ; flower arrangements by Ola Howells (Woodbridge : Garden Art Press, 1996)

All of these titles are available in the Miller Library.

Date 2019-08-07
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Plant Answer Line Question

Keywords: Rosa

I am using a Grandiflora rose named Prominent (Kordes) as a foreground planting; a climber (Autumn Sunset) is in the background. I love the color and the shape of Prominent's blooms, but the blooms are sparse and plants are spindly compared to the healthy climber. Is there anything wrong with planting a new Prominent bush a few inches from each existing bush, to create fuller looking plants?


Below are some general guidelines on spacing for roses. Since you are planting a Grandiflora near a climbing rose which I am assuming has a structure to climb, you could probably get away with planting a bit closer than the 30"-36" spacing recommended between two Grandifloras, but if you plant right up against the other rose, I imagine it would be problematic due to inadequate air circulation, which could lead to diseases. Here is what a publication of the University of Illinois Extension has to say:

"A general rule of thumb suggests that roses should be planted about 24 inches apart. This spacing will vary depending on the type of rose you are planting. Old garden roses will need wider spacing, while miniatures can be planted closer. Sufficient space between plants allows for good air circulation, an excellent first step in disease control."

Suggested Spacing for Roses, from Jackson and Perkins:

Hybrid Teas & Grandifloras
Space: 30" -36" apart
Coverage: 6 -10 sq. ft.

Space: 24" -30" apart
Coverage: 4 -6 sq. ft.

English Rose
Space: 36" apart
Coverage: 10 sq. ft.

Space: 4' -5' apart
Coverage: 12 -15 sq. ft.

Space: 24" apart
Coverage: 4 sq. ft.

Space: 30" -36" apart
Coverage: 6 -10 sq. ft.

Space: 24" -30" apart
Coverage: 4 -6 sq. ft.

Space: 12" -18" apart
Coverage: 1 -2 sq. ft.

Tree Rose
Space: 3' -5' apart
Coverage: 10 -15 sq. ft.

Space: 3' -4' apart
Coverage: 10 -12 sq. ft.

Space: 2.5' -3.5' apart
Coverage: 6 -11 sq. ft.

Date 2020-01-16
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Plant Answer Line Question

Keywords: Rosa

I would like more information on Rosa chinensis 'Mutabilis', particularly regarding how it performs in a Seattle garden. I am most concerned about black spot and any other diseases.


I am currently growing this rose for the first time, and it is blooming profusely. I have needed to keep on top of the aphids (hand-squishing), and there are a few yellowed leaves which drop (and which I have been picking up and destroying as soon as I see them). Here is what the book Roses for the Pacific Northwest by Christine Allen (Steller Press, 1999) has to say about this rose:

Few old roses flower so continuously--cold weather merely turns the buds a paler hue and, although they don't then open, they remain fresh-looking on the bush for weeks. It hates cold wind, but will take a surprising amount of shade, forming an open, leafy shrub with soft red stems and red-tinged foliage, impervious to disease.

I would not go as far as to say it is impervious to disease, but my impression is that it is relatively disease-resistant. I am truly enjoying the look and fragrance of this rose in my garden. Links to additional information:

Oregon State University: Disease-resistant roses make gardening life easier
An article by Valerie Easton in the Seattle Times

Date 2019-09-18
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Plant Answer Line Question

Keywords: Rosa

I was wondering if you could send me information about Floribunda roses. I'm doing a research paper.


We have a large selection of books on roses here in the Elisabeth C. Miller Library. You are welcome to come in and browse as well as borrow books.

The Seattle Rose Society says the following about Floribunda roses: Floribunda roses combine the best aspects of their parent plants: the Hybrid Tea rose and Polyantha rose. They receive their flower form and foliage from the Hybrid Tea while taking after the Polyantha in increased hardiness and exuberance of blooms. This link is to their lists of recommended roses for the Puget Sound region, including the best Floribundas.

Here are additional links which may be useful.

Roses and everything rose & gardening related

American Rose Society

Most of our books have at least a little information on Floribundas, but none is specifically and exclusively about them. I recommend The Companion to Roses by John Fisher (Salem House, 1987) for history of rose classification, and Jeff Cox's Landscape with Roses (Taunton Press, 2002) for practical ideas on using roses in the garden, and recommendations of specific Floribundas which do well. Cox says that Floribundas are the best of the Modern roses for most landscaping situations because of their hardiness, free-flowering habit, bushy form, and flowering season. They work well both as specimen plants and in combination with other flowers and shrubs in beds and borders. Most grow 2-4 feet tall, and are dense enough to be used as hedge plants. Varieties range from single, semi-double, to double flowers. Some are fragrant. Specific varieties mentioned by Cox are 'Gruss an Aachen,' 'Iceberg,' 'Queen Elizabeth,' 'Marmalade Skies,' 'Showbiz,' 'Betty Prior,' 'Escapade,' 'Nearly Wild,' 'Lilac Charm,' 'Europeana,' 'Sunsprite,' and 'Apricot Nectar.'

Date 2019-05-18
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Plant Answer Line Question

Keywords: Rosa

Do I need to take my miniature tea roses indoors for the winter?


Your message doesn't mention where you live, so I don't know how cold your winters are. Bringing your roses into the house can be problematic, because we tend to keep our homes too warm for the plant, which wants to go dormant in winter. A cold but sheltered spot may be a better choice. If you live in the Pacific Northwest, you can keep your roses outdoors year-round. Christine Allen's Roses for the Pacific Northwest (Steller Press, 1999) says that miniature roses are extremely hardy, hardier than many larger roses. They can survive winter in an unprotected pot unless the soil freezes all the way through.

The following information from New Mexico State University Extension offers similar advice. Excerpt:

"The miniature rose is often hardier than the common hybrid tea rose, so it will survive but not bloom through the winter in most parts of New Mexico. It requires a cool, dormant period and will do poorly if brought indoors where it will stay warm. I have also noticed that if it is indoors during the winter, it is often attacked and even killed by spider mites. Other insects also become a problem when plants are indoors.

"You have several options. One is to leave it in its pot and keep it outside in a protected location. Plants in pots are more subject to freezing during the winter because the soil in the pot can freeze completely and drop to a lower temperature than soil in the ground unless the pot is kept in a protected location. Plants in the ground may have the soil freeze around the base of the plant, but the roots are often not frozen. A sunny location that allows daily warming and nightly freezing of the soil in the pot is not good. You will also need to make sure that the soil in the pot does not dry completely during the winter. Roses need some moisture in the soil around their roots even in the winter. Soil in flower pots dries more quickly than in the ground.

"Another option is to plant the rose in the soil where the soil temperature will remain more moderate and the soil will dry slowly. It is late in the season for this, but it can be done. Don't let it dry after planting, and by applying a layer of organic mulch (bark, straw, etc.) around the base of the plant, you can help maintain moderate temperatures and prevent sudden temperature changes in the root zone.

"Finally, you can keep the rose in a protected, cool location, allowing it to become dormant for several months, then prune it and bring it indoors to begin blooming early in the spring. This allows it to have its winter rest, but you can enjoy its flowering earlier than if it stayed outside. Replanting in a large pot may be helpful to allow more root growth. A miniature rose is called miniature not for the size of the plant but for the size of the flowers. Some miniature roses can become fairly large plants and need a large root zone to support growth and flowering. That is why planting outdoors may be the best choice in the long run, but repotting it allows a potentially useful compromise."

Date 2019-05-18
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Plant Answer Line Question

Keywords: Rosa, Plant diseases--Control, Fungal diseases of plants

What can I do about black spot on my roses? I heard that burying banana peels in the soil might help.


According to The Organic Gardener's Handbook of Natural Insect and Disease Control (edited by Barbara Ellis; Rodale Press, 1996), there are several steps to dealing with black spot on your roses. First, avoid wetting the leaves, and do not handle the plants when foliage is wet. Prune the plants to make sure there is good air circulation. Make sure the roses are in sun, and are not shaded by large shrubs or trees. Avoid using high-nitrogen fertilizers, and only fertilize based on a soil test's indications. If you expect an appearance of black spot (based on past experience), spray plants weekly with sulfur or fungicidal soap. Once you see symptoms, it is hard to control black spot. Remove and dispose of any affected parts of the plant (don't compost). Make a solution of 1 teaspoon baking soda in a quart of water, and spray the infected plants well.

University of California, Davis's Integrated Pest Management website says the following about black spot (Diplocarpon rosae):

"The fungus requires free water to reproduce and grow, so leaves should not be allowed to remain wet for more than 7 hours. (When hosing off aphids, do it in the morning so leaves have a chance to dry by midday.) Provide good air circulation around bushes. Remove fallen leaves and other infested material and prune out infected stems during the dormant season. (...) Miniature roses are more susceptible than other types, although a few varieties are reliably resistant to all strains of black spot.(...) A combination of sodium bicarbonate or potassium bicarbonate plus horticultural oil (as discussed above under "Powdery mildew") or neem oil has also been shown to be effective in reducing black spot."

Brooklyn Botanic Garden has information on natural disease control, including the following:
"Baking soda (sodium bicarbonate) is non-toxic, readily available, and very inexpensive. It can be effective against powdery mildew and somewhat useful against black spot. If you repeatedly spray leaves with bicarbonate, though, it will eventually reach the soil below, where it can accumulate and lead to slower plant growth. Bicarbonate can form insoluble particles with calcium and magnesium ions when it concentrates in the soil, making these important nutrients unavailable to plants. High levels can also prevent plants from absorbing iron and can lead to chlorosis.
Bicarbonate is most likely to build to damaging levels in drought-stressed areas where there is little rain to flush it away. It is also likely to build up when applied in a small area, and when used in conjunction with drip-type irrigation. Garden situations are so complex that it is hard to predict the point at which you will see adverse effects. Stop applying bicarbonate sprays, however, at the first sign of plant damage or lower quality blooms."

Brooklyn Botanic Garden also mentions a beneficial bacterium which may provide some help:
"Preliminary research shows that the beneficial bacterium Bacillus laterosporus (sold as Rose Flora) is as effective at protecting black spot-susceptible rose cultivars as some chemical fungicides. It probably protects against black spot through competition, but this agent is still relatively new and experiments detailing its mode of action have not been completed. As a ground spray, it can help control new sources of black spot infection. As a foliar spray, it seems to be more effective when mixed with the antitranspirant sold commercially as Wilt-Pruf. The powdered formulation can cause eye irritation, so use eye protection when mixing solutions and applying."

About the practice of using banana peels to control black spot on roses, I found the following item on Gardening Folklore from Ohio State University Extension, which suggests the peels might be a good fertilizer, but does not say they will control the fungal problem.
"Placing several banana peels in the planting hole was popular among rose growers in the 18th century, but they had no idea why the peels seemed to yield healthier roses. Today, we know that banana peels contained many useful nutrients, including calcium, magnesium, sulfur, phosphates and sodium. The peels rot quickly which means these nutrients are readily available to the plant."

Some sources recommend using compost tea or milk sprays on black spot-affected leaves, but Washington State University Horticulture Professor Linda Chalker-Scott dismisses these methods as ineffective. She also states in an article in Master Gardener magazine (Spring 2009) that baking soda sprays may only be of limited efficacy in combatting black spot. Studies have shown that it works better when combined with horticultural oil.

To sum up, I would pay attention to the cultural practices (not wetting the leaves, etc.). You can try a baking soda spray (always test on a small area of the plant first), but it may not have lasting power as a treatment. Prof. Chalker-Scott mentions that coarse organic mulch (such as wood chips) reduces incidence of black spot, so you may want to adopt this mulching practice.

Date 2019-08-23
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Plant Answer Line Question

Keywords: Sawflies, Rosa, Insect pests--Control, Azadirachta indica

I think my rose leaves are being devoured by rose sawfly, and I was wondering if spraying 'Rose Defense' on them would help.


Rose Defense is a Scott's product that contains Neem (as well as other ingredients). There is some evidence that Neem is effective against sawfly larvae. As with any pesticide, you should follow the directions on the package carefully (and note that this product may be harmful to humans, domestic animals, bees, and the environment, depending on the route of exposure).

You might want to start out with the least toxic approach first, that is, handpicking and spraying with water. Once larvae are knocked off the roses, they will not climb up again. If this doesn't seem to be helping, then you could choose a Neem-based spray or insecticidal soap, keeping in mind that the Neem product is toxic to bees, and should not be applied when bees are active.

According to University of Minnesota Extension, sawflies are best controlled when young. You can simply pick them off by hand or dislodge them with a stick or a stream of water. If using water be sure to spray early enough in the day for the foliage to dry by sunset. This will prevent favorable conditions for fungal development. Horticultural oil, insecticidal soap and azadirachtin (sometimes called neem), are among the less toxic insecticides to treat young sawflies. Azadirachtin is slower acting. Bacillus thuringiensis (Bt) is effective on young lepidoptera caterpillars but NOT on larval sawflies.

Cornell University's Resource Guide for Organic Insect and Disease Management (formerly available on the Cornell website) also discusses the uses of Neem. Here is an excerpt:
"Neem products are generally sold as emulsifiable concentrates. Neem oil soap is sold as a water-soluble liquid concentrate. While Copping (2001) reports no known incompatibilities with other crop protection agents, phytotoxicity may be a problem when combining neem oil or soap products. Read labels for specific application guidelines including determination of re-entry interval and pre-harvest interval. Range of efficacy will depend on the susceptibility of species in question and environmental conditions at time of application. However these are points to follow:
Make multiple applications. Frequent applications are more effective than single sprays because neem does not persist well on plant surfaces. Like most other botanically derived materials, it can be rapidly broken down by sunlight and washed away by rain (Thacker 2002).
Use against immature insects. Azadirachtin-based insecticides act on immature stages of insects more effectively than on eggs or adults. To reduce a build up of populations it is important to make treatments to crops targeting insects in an early stage of their life cycle. For instance, neem would likely have little effect on an infestation of striped cucumber beetle adults; however if applied to potato plants early in the season, it has been shown to greatly reduce larval activity of Colorado potato beetle.
Begin applications before pest levels are high. Antifeedant and egg-laying repellant effects show best results in low to moderate pest populations.
Neem is reported to work best under warm temperature conditions (Schmutterer 1990)."

There are quite a few different species of sawfly, and I would guess that the rose sawfly is so named because rose bushes are its primary feeding ground. If you aren't sure what is eating your roses, you may want to take samples of the affected leaves to your local county extension agent before you begin to treat the problem. You may find the images on the self-described Buggiest Rose Website helpful in comparing with the leaf damage you are seeing.

Date 2019-10-31
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Plant Answer Line Question

Keywords: Rosa, Insect pests--Identification, Fungal diseases of plants

I have several roses that bloom just fine but one particular rose bush produces buds that never open. Why is this happening?


It is possible that your rose has a problem with insects like thrips, which can cause buds not to open. If you see tunneling in the buds (holes in the petals), it could be caused by beetles. There is also a possibility that a disease is causing the problem. Fungal infections like botrytis blight can result in buds which do not open, but you would probably notice signs of the fungus during warmer temperatures, such as gray-brown fuzzy growth, and blotched petals or drooping buds. The Northwest Center for Alternatives to Pesticides provides information describing various rose problems, and organic solutions.

Here is a description of botrytis blight from University of California, Davis Integrated Pest Management. This is a brief excerpt:
"Botrytis blight, caused by the fungus Botrytis cinerea, is favored by high humidity. Affected plants have spotted flower petals and buds that fail to open, often with woolly gray fungal spores on decaying tissue. Twigs die back and large, diffuse, target-like splotches form on canes. Reduce humidity around plants by modifying irrigation, pruning, and reducing ground cover. Remove and dispose of fallen leaves and petals. Prune out infested canes, buds, and flowers. Botrytis blight is usually a problem only during spring and fall in most of California and during summer along coastal areas when the climate is cool and foggy."

The Olympia Rose Society also has information on these potential causes of failed buds. Below is their description of thrips:
"Buds do not open, or flowers are deformed. Petals have brownish yellow streaks and small dark spots or bumps. White and pastel roses are particularly susceptible. Thrips (are) tiny orange insects with elongated bodies. Thrips feed at the bases of rosebuds and on the petals of open flowers. They seem to be attracted to light-colored blossoms."

The Organic Gardener's Handbook of Natural Insect and Disease Control edited by Barbara Ellis (Rodale Press, 1996) suggests encouraging natural predators of thrips and, if the infestation is severe, spraying weekly with a safer insectidical soap or pyrethrin-based product. This same resource suggests that if your roses have botrytis blight, you will see the buds turn brown and decay instead of opening, and you should pick off and dispose of any diseased buds. They recommend spraying with sulfur once a week during the growing season.

A few things that are always a good idea when growing rose:

  • make sure there is good air circulation around your plants
  • don't water from above the plants (keep the leaves dry)
  • always clean up around the plants--don't let leaf debris or any diseased buds lie on the ground under the rose bushes

This site has many pictures of rose pests and diseases for you to compare with what you are seeing on your plant. Since I cannot diagnose the problem without seeing the plant, I recommend that you take samples of the affected buds to a Master Gardener Clinic.

Date 2019-12-27
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Plant Answer Line Question

Keywords: Rosa, Pesticides and the environment, Fungal diseases of plants

I heard somewhere that the fungicide Rose Pride was less toxic to beneficial insects than plain baking soda. Is this true? I'd like to continue to use it in my garden.


Rose Pride is the chemical Triforine. I was not able to find any articles which suggest it is safer for beneficial insects than baking soda. Pesticides Action Network's Pesticides Database indicates it is toxic in varying degrees to some forms of aquatic life. It is on the PAN List of "Bad Actor" pesticides, which means it belongs to a group of pesticides classified as most toxic (because they are known or probable carcinogens, reproductive or developmental toxicants, etc.). The Extension Toxicology Network also has a profile for this pesticide. Here are excerpts:
"In the United States, triforine is marketed for use on almonds, apples, asparagus, blueberries, cherries, hops, ornamentals, peaches and roses. Triforine is a 'restricted use' pesticide (RUP) with an EPA toxicity classification of I (highly toxic). Check with specific state regulations for local restrictions which may apply. Products containing triforine must bear the Signal Word 'Danger' on their label.
Triforine and the formulated product Saprol are considered of low hazard to honeybees and to the predatory mite Typhlodromus pyrii. It is also of low hazard to earthworms at recommended dose rates."

My comment would be that "low hazard" is not the same as no hazard, and since there are many other areas of concern with this highly toxic product, it would be best to find an alternative. Locally, the Woodland Park Rose Garden converted a pesticide-dependent landscape to an organic one, and the roses look better than ever. (See an article about the garden from the Seattle Times.) Many gardeners are learning to live with a bit of black spot on their roses, and manage the disease by maintaining good garden hygiene. Don't leave fallen leaves on the ground. Give your roses good air circulation, and keep the leaves dry when you water your plants. Mulching with wood chips can help, too, since they may prevent water from splashing up onto the leaves.

When deciding whether to treat a garden problem with pesticides, the "Precautionary Principle" provides an important perspective:
"When an activity raises threats of harm to human health or the environment, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically."

Date 2019-10-31
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Plant Answer Line Question

Keywords: Rosa, Mosaic diseases, Pests

My roses were diagnosed with both rose slug and rose mosaic. I would like to know your thoughts about treatment of these conditions, as it was suggested that I just remove affected leaves, and I am looking for a more effective solution.


I will summarize what Christine Allen's Roses for the Pacific Northwest (Steller Press, 1999) says about these two problems:

Mosaic virus:
This disease infected the roots of your rose when the plant was grafted; the symptoms do no show up for a year or two. The problem is widespread anywhere that rootstocks are developed from cuttings (rather than seed). (In Canada, apparently, most rootstocks are grown from seed, so they have far less of a problem with the disease.) The disease is incurable, and affected plants will have yellow patterning on their foliage. Other plants in the garden cannot "catch" the disease. Sometimes the symptoms disappear by midsummer, but recur the following spring.

Rose slug:
The greenish-white worms are actually sawfly larvae, and they can skeletonize leaves. They aren't caterpillars, so controls that are used for caterpillars (such as Bt) won't help. Insecticidal soaps can kill them, but only by making contact, so this means repeated spraying. It is best to do this in early evening when the larvae are most active, and may be seen on the top surfaces of the leaves. Pyrethrins are effective, but they also are acutely toxic to aquatic life, moderately toxic to birds, and may kill beneficial insects such as honeybees [my comments, not the author's], so they should be a choice of last resort. The Environmental Protection Agency has additional information on pyrethroids and pyrethrin.

To prevent or mitigate rose slugs, clean up leaf litter and other debris several times a season to eliminate pupae and interrupt the life cycle. Hoe the soil gently and not deeply, and apply annual mulch early in the year.

Date 2019-05-22
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Plant Answer Line Question

Keywords: disbudding, Rosa

I've been removing all the small, spiky buds and leaving the main developing bud on my rose (I think it's a Floribunda, but I'm not sure). My husband told me I was doing the wrong thing. Is he right? I thought I'd heard that removing the ancillary buds would give me a better-looking single bloom, like the long-stemmed roses you see in displays.


I'm a lazy grower of roses, and so it would not occur to me to disbud in order to have one single larger rose. But you are correct that this is in fact done in some cases. I found a brief item in Rose Magazine online which illustrates the practice (it seems to be used mainly for roses being used in displays, where a kind of perfection is desired). Note the following, about Floribunda roses, which describes exactly the opposite procedure:
"On roses that produce multiple blooms, like those of Floribundas or Grandifloras, it is the terminal bud that is removed. On these roses, the terminal bud will open first. By the time surrounding blooms form the terminal rose is almost fully blown. The result is a floral spray with a hole in the center. By removing this terminal bud early in its formation, the rose's energy goes toward those that remain. The result is a floral spray that is full -- without the hole in the center."

The website of the Desert Rose Society also describes disbudding.
"The practice of disbudding applied to roses can produce some impressive results in the size and quality of the bloom. This is how you get those big lovely long-stemmed roses. When disbudding for one bloom to a stem roses, such as hybrid teas, you remove the side buds that develop at the leaf axils below the main bloom. This is done by rubbing the tiny buds out from of the angle created between the leaf and stem. I find my thumb works best for getting right in there. The earlier you do this in the development of the side buds the better, for you will leave less of a disbudding scar or black stub. How many buds do I remove? Enough that you will have the desired stem length with no side buds. In a rose show, a single bloom on a stem will be disqualified if it has side buds, with the exception of old garden roses and shrub roses.

When disbudding roses that bloom in clusters like the floribundas, it is a little different process. You have to look at the stem and see how many buds there are. If there is a central bud and only one or two side buds, remove the side buds and go for a one bloom stem. When presented with many buds and a central bud, remove the central bud and make this stem into a spray (or cluster) of blooms. The central bud would normally bloom first and be faded when the rest of the buds open. A spray, for show purposes, must contain two or more blossoms and three or more blossoms are best. If trying for a spray for show be sure that the multiple buds have at least three buds of about the same size so they will be open at the same time to give the desired blossom count."

For the meticulous home gardener or professional rose exhibitor, you may find this information on the American Rose Society's judging criteria of interest.

To sum up, the answer to your question about whether or not to disbud seems purely an aesthetic choice.

Date 2019-06-12
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Plant Answer Line Question

Keywords: Rosa, Fragrant flowers, Air pollution

I wonder why my roses have lost their fragrance. My 'Double Delight' roses used to have a good smell, and now the flowers are bigger and there is no fragrance.


It does seem mysterious that a once-fragrant rose should lose all fragrance. There are many factors which might cause the perceived lack of scent. According to The Graham Stuart Thomas Rose Book (Timber Press, 1994), rose scent itself is complex, and is composed mainly of geraniol along with many other substances. It is mainly released from tiny cells on the surface of the petals: "Scent is produced mainly in the petals and is given forth when the growth of the flower and the atmospheric conditions are right. From this it will be seen why double roses have more volume of scent than singles [...] scent is especially apparent in most flowers when the air is neither too cold nor too hot [...] In extreme conditions, such as wilting, extra scent may be released [...] Usually the best fragrance is obtained from a newly opened flower growing on a healthy, well-established plant on a windless day when growth is exuberant [...] we may expect fragrance to be at its best on a day when the air is warm and moist rather than dry, when the plant will be functioning well. It is not that moist air conveys better than dry, but that the plant is giving it forth in greatest quantity."

From the above, you may want to consider the following

  • When you discovered the rose had no scent, were the atmospheric conditions optimal for the release of scent?
  • If scent is most prominent on healthy plants, are there any underlying reasons (pests, diseases, cultural problems such as overwatering, poor soil, etc.) the plant might not be at its strongest?

Other things to consider:
Environmental pollutants affect not only our sense of smell, but the fragrance emitted by flowers, as this 2008 University of Virginia study describes:
"'The scent molecules produced by flowers in a less polluted environment, such as in the 1800s, could travel for roughly 1,000 to 1,200 meters; but in today's polluted environment downwind of major cities, they may travel only 200 to 300 meters,' said Jose D. Fuentes, a professor of environmental sciences at the University of Virginia and a co-author of the study. 'This makes it increasingly difficult for pollinators to locate the flowers.'

The result, potentially, is a vicious cycle where pollinators struggle to find enough food to sustain their populations, and populations of flowering plants, in turn, do not get pollinated sufficiently to proliferate and diversify."

Another thing that you might ask is whether your rose was grafted, and perhaps you are getting a different rose coming up from the graft. The loss of fragrance and the different appearance of the flowers makes me wonder if this could be what is happening.

Date 2019-08-02
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Garden Tip

Keywords: Rosa, Plant and garden societies

What is your favorite rose? Here are a few of the World Federation of Rose Societies "World's Favorite Roses" chosen by a popular vote of the members:

rose name flower color ARS rating on a scale of 10
Double Delight Red/White Blend 8.6
Fragrant Cloud Coral 8.1
Pascali White 8.1
Peace Pink/Yellow Blend 8.3

Date: 2007-03-05
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Garden Tip

Keywords: Rosa, Plant and garden societies, Reference books

Rose resources:

  • www.everyrose.com - the best online database with photos, sources and gardeners' comments
  • www.justourpictures.com - great photos of roses
  • American Rose Society

  • Books:
  • The Graham Stuart Thomas Rose Book (Sagapress, 1994) -A revised edition from this late great British plantsman
  • Reliable Roses by Philip Harkness (Firefly Books, 2004) - Excellent photos and organized text describe 75 good roses
  • Roses for Washington and Oregon by Brad Jalbert & Laura Peters (Lone Pine, 2003) The best 144 roses for the Northwest
  • Lois Hole's Rose Favorites (Lone Pine, 1997)- Has all the usual rose profiles and care information, plus lots of fun facts and lore.

  • In Seattle:
  • The Seattle Rose Society meets at the Center for Urban Horticulture (3501 NE 41 Street) on the third Tuesday of the month at 7:30pm (except July and Dec.)
  • The Woodland Park Rose Garden, adjacent to the Zoo, is open to the public from 7 am to dusk, everyday. Admission is free.

Date: 2007-04-03
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Garden Tip

Keywords: Rosa, Garden design, Amelanchier, Sedum, Hydrangea

It's easy to plant a garden that is colorful and interesting in June, more difficult is designing a garden that shines in October. Read Autumn Gardens by Ethne Clark (Soma, 1999) to learn both design principles and the best trees, shrubs, perennials, bulbs and grasses to plant in fall. Oakleaf hydrangea, Canadian serviceberry, species roses, and sedums are just a few of the plants featured that will extend the garden interest beyond Labor Day.

Date: 2007-07-13
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Growing roses in the Pacific Northwest   by Nita-Jo Rountree, 2017

Reviewed by: Brian Thompson on 2017-07-01

Growing roses in the Pacific Northwest cover Nita-Jo Rountree move to the Bellevue, Washington 15 years ago after many years as a Master Gardener and the owner of a landscape design and installation company in Atlanta. She quickly learned to separate reality from the myths of our climate and she has used that knowledge to specialize in roses, one her favorite plants – perhaps her very favorite plant (she’s a bit coy on this subject; I know she loves hydrangeas, too).

She has chosen an impressive list of roses in all classes, all bred for health, or that have proved their durability in our region without a lot of fussing. Many of them are recent introductions that reflect the work of hybridizers for the home gardener, but she doesn’t ignore species or historical roses.

I have a passing knowledge of rose varieties, mostly from a brief period of heavy immersion in gardening with roses many years ago. At the same time, I learned a lot about the frequent spraying and other chemical rites of rose growing, as this was the expectation in almost every rose books of the time. Today, I only know a handful of Rountree’s recommendations. There is a good reason for this as her newer, recommended varieties don’t need the level of coddling I learned, thus avoiding the potential damage to the garden environment, the wildlife of the garden large and small, or to the gardener.

Rountree is emphatic in her most important advice. “Remember: The most important key to successful rose growing is choosing the right rose for the right place. Many books and articles about roses give generic advice for growing roses in a wide range of climates. They are of little specific help for growing roses in the Pacific Northwest.”

Excerpted from the Summer 2017 Arboretum Bulletin.

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