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Elisabeth C. Miller Library

Archives: Plant Answer Line Q & A

Plant Answer Line questions and answers.

butterfly conservation in the Pacific Northwest

I have become interested in helping with the conservation of monarch butterflies, whose caterpillars feed only on milkweed. We are supposed to plant milkweed. I am also gradually converting my small Seattle garden to a native-plant garden. Do these two goals contradict each other? Are any of the milkweeds native to Seattle and vicinity? Would monarchs themselves be an exotic species here?

It’s wonderful that you want to help with butterfly conservation. Monarch butterflies are not frequently seen in the Puget Sound region and, as you may be aware, it is too cold for them to overwinter here (they need an air temperature of at least 50 degrees Fahrenheit, according to Jerry Sedenko’s The Butterfly Garden [Villard Books, 1991]). However, you can do several things to make your home landscape hospitable to the pollinators we do have in our area, including not using any pesticides in your garden and persuading your friends and neighbors to refrain from using them also.

The Monarch Joint Venture project links to the Xerces Society’s Milkweeds: A Conservation Practitioner’s Guide which has information on milkweed species and their natural habitats. The plants recommended by the MJV for the West are Asclepias speciosa and Asclepias fascicularis but these plants may not be successful in the Puget Sound region. Both species are found mostly east of the Cascades as these maps from the USDA show. (click on the detail maps for Washington State)

The Xerces Society for Invertebrate Conservation has useful information(now archived) about Western Monarchs, as well as separate pollinator conservation resources (for different types of pollinators–not Monarchs) for the Pacific Northwest.

You might be most effective in supporting the Monarch conservation effort financially but devoting your gardening efforts to conservation of species that are native to our area. Here are the Xerces Society’s list of Pacific Northwest butterflies and bees.

The Puget Sound Beekeepers Association has information on bee-friendly gardening.

The issue of using native plants in our urban gardens is a complex one. How do we define the native status of a plant? Sometimes the only plants available in nurseries are cultivated varieties of native species: are they still ‘native?’ Are plants that have naturalized in our area native? Do we have the ideal conditions in our garden to sustain native plants?

My personal outlook on this is that it’s best not to think too rigidly about what is native and what is not, but instead to be vigilant about what is overly aggressive or definitively noxious and invasive, and to try to grow a diverse range of plants that will thrive without excessive watering, fertilizing, and fuss, and select plants (native and otherwise) will attract birds, beneficial insects, and local species of butterfly. Here is Washington State University Extension horticulturist Linda Chalker-Scott’s essay on the topic of native plants.

fasciation or crested growth in plants

The ends of some of my Daphne odora branches look like several branches fused together. What causes this, and is there something I should do?

What you are describing sounds like fasciation, which is a kind of genetic mutation. Professor T. Ombrello of the department of biology at Union County College describes this condition:
Excerpt:
“One interesting type of mistake that is occasionally found in plants is known as a fasciated or crested growth form. It is usually the result of a growing point changing from a round dome of cells into a crescent shape. Subsequent growth produces a flat stem. In some cases fasciation is the result of several embryonic growing points fusing together, with the same flat-stem appearance. [… ] What causes plants to produce fasciated stems? For the most part, we just don’t know. Fasciation has been induced experimentally by applications of plant hormones, severe pruning, wounding, and atypical day lengths. Most, however, appear by chance with no obvious cause.”

University of Arkansas Extension addresses the phenomenon of fasciation.

Possible causes for this condition:

  • bacterial infection
  • inherited genetic trait
  • herbicide, insect, or physical damage to the growing tip
  • garden conditions that favor rapid growth
  • spontaneous mutations

There are good illustrations and explanations on the blog of Tentative
Plant Scientist, as well.

You don’t need to do anything, unless you would like to remove the odd-looking growth. You may want to look into whether herbicide has been used, or if there have been insects feeding on your Daphne. Also, avoid over-fertilizing, which could promote excessively fast growth.

variation of color in Hydrangeas

Is the color of every type of Hydrangea variable, according to the pH of garden soil? Or are some species or varieties reliably the same color, no matter where they are planted?

I think the main species of Hydrangea whose color gardeners sometimes try to alter is Hydrangea macrophylla, also known as hortensia, bigleaf, or mophead hydrangea. According to Van Gelderen’s Encyclopedia of Hydrangeas (Timber Press, 2004), most cultivars of Hydrangea macrophylla are naturally pink, even in slightly acidic soil. “The key factor in flower color is not the acidity of the soil, but a plant’s accessibility to aluminum sulfate.” The plant will not produce blue flowers if it has access to aluminum sulfate but the soil is strongly alkaline, as the calcium of high pH soils will bind with it, preventing the plant from absorbing it. The authors state that “some cultivars easily turn blue under the right conditions,” while others do not. White-flowered cultivars of different Hydrangea species usually retain their color, though the flowers may become flecked with red or pink toward the end of the season.

Hydrangeas: A Gardener’s Guide, by Toni Lawson-Hall and Brian Rothera (Timber Press, 1995) says that while several species of Hydrangea may have some variation in color, Hydrangea macrophylla ssp. macrophylla and its cultivars (including mopheads and some of the lacecaps) have potential for the most dramatic changes. However, “there are some innate preferences within the individual plants […] and not every mophead or lacecap will change colour in response to a gardener’s alchemy.” The authors do mention a few plants which display red flowers even in acid soil, such as cultivars of Hydrangea serrata: ‘Preziosa,”Grayswood,’ and ‘Beni-Gaku.’ Among the H. macrophylla cultivars that stay red in acid soil are: ‘Alpengluhen,’ and ‘Altona.’ Cultivars which are considered most reliably blue on acid soil also need a low level of phosphate: H. macrophylla ssp. macrophylla ‘Gentian Dome’ and ‘Marechal Foch’ (both deep blue), ‘General Vicomtesse de Vibraye’ (pale blue), and Hydrangea serrata ‘Diadem’ and ‘Blue Deckle’ (blue lacecaps).

Azara dentata yellowing and dropping of leaves

I have an Azara dentata or lanceolata. The leaves on the upper branches are drooping and on one limb, the leaves are yellowing and dropping off. The plant is about 15′ tall. This is not the normal winter leaf drop. What could be happening?

We can’t diagnose plant diseases remotely, so you might need to bring samples for the Master Gardener diagnostic clinic. However, there are some things to consider:

Is the soil too rich or heavy for the Azara? They prefer “a light mineral soil, low in fertility, and resent heavy and overly fertile soil in garden situations,” according to Sean Hogan’s Trees for All Seasons (Timber Press, 2008). They like afternoon shade, as well. Hogan says that Azara dentata likes regular deep watering, and protection from scorching afternoon sun. He says that Azara serrata and A. dentata are often confused: A. serrata has narrower, more glabrous leaves whose serrations are forward-pointing.

I grow Azara microphylla, and it has always dropped some yellowed leaves. The specimen here at the Center for Urban Horticulture also does this. Drooping branches don’t sound good, and if your plant is dropping a large proportion of leaves, you should seek advice from the Master Gardener Clinic. Meanwhile, consider whether anything in your garden has changed recently: use of fertilizer or herbicide, change in sun exposure, soil amendments, etc. This will help narrow down the cause of the problem. Bringing a photo of the whole plant along with your sample is also a good idea.

pruning Arbutus unedo

I have an Arbutus unedo ‘Compacta’ planted in my garden, close to the property line. My neighbors want me to shear the top and sides so that they can see the view beyond it while seated on their sofa. I really don’t want to do this, but I need to provide a convincing argument that shearing is not the best way to prune my Arbutus.

It’s difficult to imagine topping and shearing the compact form of Arbutus unedo which is unlikely to exceed 10 feet. Ideally, it would need no pruning whatsoever. Local pruning expert Cass Turnbull of Plant Amnesty classes Arbutus unedo with other “tree-likes,” shrubs or small trees which should be maintained with a tree-like shape. Below are excerpts from her recommendations on pruning (and there is a brief guide on Five Reasons to Stop Topping as well):

“DON’T: Ornamental trees should never, ever be topped. And shrubs should rarely be sheared (except real topiary and formal hedges). Stripping all of the side branches off of a mature pine or any other tree or shrub, is also a no-no. Stripping is not to be confused with selective thinning, which can also make shrubs and trees look open and Oriental.

III. TREE-LIKES

Best let to get big. Not to be pruned heavy-handedly. Good selective pruning can open them up and make them look less oppressive, can train branches around gutters and off of houses, and can bring more beauty out of your plant. These shrubs are the hardest to do. Never remove more than 1/8 total leaf surface in one year. It stresses them or it can cause a watersprout-rebound effect — ick! Tree-likes have stiffish branches, generally. Examples of tree-likes include rhododendrons, andromeda (pieris), magnolias, deciduous Viburnums, camellias and witch hazel.

Most tree-likes just need to have all of the dead wood taken out.

If you still want to do more:

Take out suckers (straight-up, skinny branches from the base and trunk of the shrub or tree.

Take out any big crossing, rubbing branches and double leaders (two main top branches with a narrow branch-crotch angle) on trees.

Take back or remove any branches hanging on the ground, if only up 1/2”.

Take out the worst of the smaller crossing, rubbing branches — choosing the healthiest and best placed branch to remain.

Prune to shorten or completely remove the worst wrong-way branches that start from the outside of the shrub, and go the wrong way back into the center and out the other side. Sometimes a side branch has a smaller branch that heads too far up into the next “layer”, or goes too far down. You can cut some of these off to add more definition to your shrub’s branches.

If you have two parallel branches rather close together, it may look better to remove one. If you, have three parallel branches you may want to remove the center one. This will make things look nicer.

Before you finish, stand back and observe. If necssary, you may sparingly shorten some branches on tree like shrubs (not trees). Cut back to a side branch.”

Another resource, Peter McHoy’s A Practical Guide to Pruning (Abbeville Press, 1993), says that Arbutus unedo “can be trained with a single trunk, as a multi-stemmed tree, or left unpruned to form a dense shrub.” He does not mention shearing it like a hedge. According to The American Horticultural Society’s Pruning & Training edited by Christopher Brickell (DK Publishing, 1996), you can prune Arbutus unedo in spring, as soon as danger of frost is past (that would be early April in Seattle), but keep pruning to a minimum. Some people choose to remove lower branches to create a taller trunk on younger trees.

Your neighbors may be under the misapprehension that shearing will control the size of the plant. In Cass Turnbull’s Guide to Pruning (Sasquatch Books, 2006), the author says, “Because shearing is nonselective heading, it will stimulate bushy regrowth, creating a twiggy outer shell on sheared plants. This layer of twigs shades out the interior which then becomes leafless and full of dead leaves and deadwood. Meanwhile the outher shell becomes thicker and larger every year because, as it is sheared repeatedly, it must be cut a little farther out to retain its greenery. This dense, twiggy outer shell makes size reduction difficult because cutting back too far exposes that ugly dead zone inside the shrub. […] Therefore, shearing is not a good way to control the size of a shrub. […] Shearing is also a drain on the health of plants.[…] Shearing plants creates the antithesis of a healthy environment, making shrubs more prone to insect attack, deadwood and dieback. It adds a general stress on plants because the rapid, profuse regrowth promoted by repeated heading depletes their energy, and their resulting weakness and tender growth makes them more susceptible to injury from freeze or drought. […] shearing often defeats the purpose of shrubbery, usually by cutting off the flowers, but other characteristics get subverted as well.” If these are not reasons enough, it is not cost-effective to shear, as it must be done repeatedly.”

You may wish to contact Plant Amnesty to obtain a referral for a consulting arborist who will speak on your behalf.

trees for durable treehouses

Our grandchild is a toddler. We want to plant a tree that would be large enough to be used for a treehouse two years from now. We were thinking of planting a sycamore, but are there other trees that would grow fast and be usable for this purpose?

Most trees that grow extremely quickly have very weak branches (poplar, willow, elm and others), and some of these trees are considered invasive or noxious (like Empress tree [Paulownia tomentosa] or tree-of-heaven [Ailanthus altissima]). Sycamore (Platanus species) typically grows 3 feet a year, which is moderately fast, and has medium branch strength. If you were to find a tree that was already a couple of years old, even after planting it and waiting 2 years, the wood would not be strong enough to support a treehouse. Also, a fast-growing tree will continue to grow larger and taller, its branches reaching higher and its trunk expanding in girth. This could cause trouble with a structure built too early on in its lifespan. Such a tree might also need a significant amount of space in the garden: its roots might reach out quite far, and its branches would also need sufficient room to spread.

You could construct a free-standing treehouse that abuts a tree, so that the branches would not need to support its weight, and visitors would still have the experience of being in the midst of foliage and branches.

The book Treehouses by Paula Henderson and Adam Mornement (Frances Lincoln, 2005) states that “most of the world’s most durable treehouses sit in healthy mature hardwoods. Good host trees include oak, fir, maple, beech, ash, and willow. Regardless of species, experts recommend that load-bearing branches have a minimum diameter of 17.5 cm. [that is about 7 inches].”

Here is an article entitled “Tree-Literate Treehouses,” about treehouse construction, from University of Georgia Forestry.

cyclamen species and their care

I brought home a cyclamen at the beginning of November (a couple of weeks ago) and it is now the saddest thing ever. All of the leaves and flowers shriveled up and went mushy. I just cut it back to the bulb-base. I bought it from a greenhouse and wanted to keep it as a house plant. It did receive filtered sunlight. Can it come back? What should I do for it to succeed and be healthy?

If you are growing the less hardy cyclamen which overwinters as an indoor plant (Cyclamen persicum) and flowers from midwinter to spring, the following information from local gardening expert Ed Hume (now archived) describes ideal conditions for growing this plant indoors:

“In a protected spot this species will tolerate temperatures to about 25 degrees outdoors. Colder temperatures and the plants must be kept indoors. Indoors they must have ample humidity. One suitable way of providing the humidity is to simply place a glass or decorative vase full of water near the plant. Then, as the water evaporates it provides the humidity the cyclamen needs. The second most important requirement of indoor Cyclamen is the need for cool temperatures. Keep them in a room where temperatures range between 55 and 65 degrees. Keep the soil a little on the moist side, but never continually wet. Water with room temperature water. When given proper care it is not unusual for this plant to continue to grow and flower for several years.”

Is it possible your plant is mushy because of too much water? Is the indoor air too hot and dry? Here is additional information about indoor or florist’s cyclamen from University of Minnesota Extension (no longer available online):

“A cyclamen won’t be too happy in a house heated much above 70 degrees F, with the dry atmosphere that goes with it. If you are unable to provide cool enough conditions, the plant will survive for a time, but eventually it will develop yellow foliage and its blooming time may be cut short. It will probably tolerate a less than ideal location for a day or two as long as you return it to a better place shortly afterwards. The plant will tolerate indoor conditions even better if you move it to a cool spot at night. Make sure to provide as much light as possible in its daytime location.

Watering incorrectly can cause many problems, especially when too much water has been applied. Always wait until the soil surface feels dry before you water, but don’t wait until the plant becomes limp. Do not water the center of the plant or the tuber may rot. A cyclamen prefers to receive a good soaking, then dry out partially before receiving a good soaking again. Allow the plant to drain over a sink or empty the water collection tray beneath the container after a few minutes. This will help prevent the roots from remaining too wet, which can lead to rotting.”

University of California, Davis’s page on Cyclamen describes diseases and pests that may affect the plants.

It is also possible you bought a summer to fall-blooming cyclamen species which one normally grows outdoors, and it may be trying to enter dormancy. Do you have information about the species you are growing? Once we know the species name, it should help us figure out what is happening with your Cyclamen.

grape vine leaf drop and dormancy

Why do grape leaves fall off the vine in fall to early winter? What happens physiologically? What triggers dormancy?

The book Oregon Viticulture (Oregon State University, 2003) describes dormancy, acclimation, and cold hardiness:
“In autumn, the vine enters dormancy–the stage with no leaves or growth activity, which extends until budburst the following spring. Despite the apparent inactivity of this stage, it can be a critical time for grapevines when they may be exposed to potentially damaging low temperatures […] There are three stages of the dormant season: acclimation, the period of transition from the non-hardy to the fully hardy condition; midwinter, the period of most severe cold and greatest cold hardiness; and deacclimation, the period of transition from fully hardy to the non-hardy condition and active growth.”

This book does not address leaf drop (abscission) nor does it explain the physiological reasons a vine enters dormancy. The Grape Grower by Lon Rombough (Chelsea Green, 2002) says only that leaf drop follows harvest time, and is part of the vine’s hardening off process: “The leaves drop, the shoots become woody to the tips, and the vine gets ready for winter. This is when the vine undergoes deactivation and reenters dormancy.” To find the scientific explanation you are seeking, it might make sense to contact a plant physiologist who specializes in vines. There are specialists at University of California, Davis’s department of Viticulture and Enology.

I consulted Plant Physiology (4th ed.) by Taiz and Zeiger (Sinauer Associates, 2006), and here is what it says about leaf abscission in general:
“These parts [leaves, flowers, fruits] abscise in a region called the abscission zone, which is located near the base of the petiole of leaves. In most plants, leaf abscission is preceded by the differentiation of a distinct layer of cells, the abscission layer, within the abscission zone. During leaf senescence, the walls of the cells in the abscission layer are digested, which causes them to become soft and weak. The leaf eventually breaks off at the abscission layer as a result of stress on the weakened cell walls.

Auxin [plant growth hormone] levels are high in young leaves, progressively decrease in maturing leaves, and are relatively low in senescing leaves when the abscission process begins.”

Here is a little information about vine dormancy, from U.C. Davis.

Excerpt:
“In late autumn, triggered by short days, petioles detach from the shoot and leaf drop occurs. The vines can no longer manufacture carbohydrates through the process of photosynthesis and are storing carbohydrates in the form of starch. This dormant state will continue until daylight hours and temperatures increase in spring, when axial buds that were formed before dormancy become activated to break.”

bark slipping and grafting

I’m looking for the definition of the term “bark slip” and the time of year when bark slip is most likely to happen. For example: “T-budding, the most popular budding method, is limited to the time of the year when the bark is slipping, however, chip budding can be used when the bark is not slipping.”

The term “bark slipping” is being used in the context of grafting.

According to Texas A & M University’s Horticulture department, bark slipping happens when the rootstock of a tree is in active growth.

Excerpt:
“Successful T budding requires that the scion material have fully-formed, mature, dormant buds, and that the rootstock be in a condition of active growth such that the ‘bark is slipping.’ This means that the vascular cambium is actively growing, and the bark can be peeled easily from the stock piece with little damage. T budding can be performed on certain fruit trees (peaches, for example) in June using cold stored budsticks and field grown seedling rootstocks. Many deciduous trees are budded in late July or early August after the current seasons buds have developed fully and are dormant using field grown seedlings that have slipping bark.”

Similar information from North Carolina State University Extension indicates that the time when bark is slipping varies, depending upon the type of tree, and upon weather conditions.

Excerpt:
“T-budding must be done when the bark will ‘slip.’ Slipping means that, when cut, the bark easily lifts or peels in one uniform layer from the underlying wood without tearing. The exact time when this condition occurs depends on soil moisture, temperature, and time of year. It varies with species and variety. Dry or excessively hot or cold weather can shorten the period when bark slips. Irrigation can be valuable in extending the T-budding season.”

In The Grafter’s Handbook by R. J. Garner (Cassell, 1988), bark is referred to as rind, but the principle is the same:
“Budding is done when the rinds readily part from the wood of the stock and when buds have developed at the base of the leaf-stalk on young shoots of the scion variety. This means that the budding season may extend from early June until September, but from the end of June until mid-August is the optimum time in normal seasons. In periods of prolonged drought the rind may not lift without tearing, and it is then wise to postpone budding in the hope that rain will come and rootstocks increase their rate of growth.”

identifying Amaranth daisy from other daisies

I am doing some research on daisies. I have had trouble finding out what Amaranth daisy (Pearly Everlasting) looks like, and how to differentiate it from other daisies.

Pearly Everlasting is Anaphalis margaritacea, which is in the plant family Compositae (also called Asteraceae), according to David Mabberley’s The Plant-Book (Cambridge University Press, 1997). Below are links to images and information about this plant.

The problem with common names like ‘daisy’ is that they may refer to a large number of different plants. ‘Daisy’ can refer to Bellis perennis, Gerbera jamesonii, Olearia species, Chrysanthemum coronarium, Felicia bergeriana, Leucanthemum vulgare, and many other disparate plants.

Below are web links to sites which may help you with plant identification. There are also many good books on the subject, and an excellent starting place is Roger Phillips and Martin Rix’s The Botanical Garden (Firefly Books, 2002).