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Elisabeth C. Miller Library

Archives: Plant Answer Line Q & A

Plant Answer Line questions and answers.

Tulip fire

The leaves and petals of my tulips are shot through with little holes. Is this some kind of insect or a disease? And what can I do to solve the problem?

 

Your tulips may have a fungal disease called Botrytis. According to Cornell University’s Plant Disease Diagnostic Clinic, Botrytis tulipae is specific to tulips and lilies. A more colorful name for this disease is ‘tulip fire.’ Cool and damp spring or summer conditions favor the development of the disease:
“Tulip fire infections cause malformations and/or large, light tan patches on tulip leaves. These patches are most noticeable on light-colored varieties. On leaves these infections are somewhat sunken, yellow to light tan, and surrounded by a water-soaked area.
On colored petals the spots appear white and on white petals they appear brown.”

Since the fungus can overwinter in plant debris, good garden hygiene may help:

  • Clean up any diseased leaves and petals, but not when they are wet.
  • Make sure you don’t water your tulips from above (of course, you can’t stop the rain–just don’t aid and abet it).
  • Avoid congested plantings–provide air circulation around your plants.
  • Ultimately, you may want to dispose of infected plants (don’t compost).
  • Rumor has it that using a grit mulch around your tulips can be helpful as a preventive measure.

The Royal Horticultural Society advises that gardeners not plant tulips in a location where Botrytis has been present for three years. According to University of Illinois Integrated Pest Management, there is no point using fungicide where the fungus is already present, but they do describe preventive uses. Always look for the least toxic option. There are some Neem-based fungicides available for home gardeners.

An article in the Telegraph by garden writer Sarah Raven gives an excellent overview of the problem and how to manage it. She highly recommends not hesitating to remove infected plants and bulbs at first discovery, the better to keep the disease from spreading. Early tulips are less susceptible, and according to Raven, the most susceptible in her garden are Darwin tulips, while Viridiflora hybrids are unaffected. Avoid cross-contaminating lilies, fritillaries, and Juno irises by planting them at a distance from your tulips.

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Cypress tip moth

My Leyland Cypress is browning and has Cypress tip moth signs. I’m worried about the brown spots, and wonder if it can survive this attack? How can I control the pests, if it might survive?

 

From what I can determine, your Leyland cypress (x Cupressocyparis leylandii) trees are probably going to
survive this attack unless they are weakened in some other way.
x Cupressocyparis leylandii in California survive the Cypress tip moth, though they can be unsightly. Since California is a bit too dry for this tree, the conditions are
not identical, but Natural Resources Canada does not
indicate that infestations are fatal. Because you said you found
evidence of tip moth (Cypress tip moth = Argyresthia cupressella), I will
assume that is what the problem is, but a bit of browning, even in
conifers, is not unusual right after trees are planted. Be sure that you
are not overwatering, as one effect of that is the same as underwatering
(i.e., tip die-back or yellowing) because too much water prevents the
plant from taking water and oxygen into the roots.

The Organic Gardener’s Handbook of Natural Insect and Disease Control
(ed. by Ellis and Bradley, 1996, p.183) says about pine tip moth
(Rhyacionia frustrana):

“Handpicking works if only a few caterpillars are present. Pruning off
and destroying infested tips in winter is a very effective control.”

I would recommend a prune-and-wait-and-see approach. April is a bit late to
prune (and puts root establishment in competition with shoot regrowth),
but you may be able to slow the infestation down, so go ahead and do
it. Watch the trees this season and then prune again in the winter next
year. Be sure to destroy (burn or bag and put in the garbage) the
debris so you don’t reinfect your tree.

A good gardening resource is the UBC Botanical Garden Forum. Personal
testimony/experience is valuable, especially if it’s regional. (You
might find it useful in the future.) Several people commenting about
x Cupressocyparis leylandii note that it is not a very desirable tree; one of its
parents, the Cupressus nootkatensis, also called Callitropsis
nootkatensis or Chamaecyparis nootkatensis, or, for that matter, plain Nootka cypress) is better. One person
recommended planting small trees in the beginning, since they grow very
fast. This might save you some money, should you have to replace your
trees. The site does not need a password; just click on “Search” in the upper right
corner.

Below is some additional information from Oregon State University about cypress tip moth. This site recommends pesticides, but from everything I read, they are not
effective without multiple treatments. Since this pest is generally not
fatal to the trees, it is probably not worth it to use chemicals which would be dangerous and time-consuming to apply. If you know something about the
life cycle of the pest, your observations will yield more information and any
manual control attempts are more likely to be effective.

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Staking Cryptomeria japonica

I recently planted a 1 gallon, approximately 2-foot Cryptomeria japonica ‘Sekkan Sugi’ in my yard. I noticed it leans. Is it normal for it to lean? Do I need to stake it so it grows straight? If so, how I would stake it?

 

According to Oregon State University’s Landscape Plants website, Cryptomeria japonica ‘Sekkan Sugi’ is meant to be upright.

An excerpt: “Seems to be some confusion about this selection(s?), listed as both fast and slow growing. Perhaps some of the confusion can be attributed to insufficient attention in handling similar Japanese cultivar names. Jacobson (1996) lists ‘Sekka Sugi’ and ‘Sekkwia Sugi’ as synonyms for the warped and twisted cultivar, ‘Cristata’; and that ‘Sekkan Sugi’ may appear as ‘Sekhan Sugi’. van Gelderen and van Hoey Smith (1996, p 216) have a picture of a cultivar listed only as ‘Sekkan’.”

Based on what Seattle-area Great Plant Picks says about Sekkan Sugi and Cristata, I think that you may want to support your tree carefully, as both cultivars are described as upright.

An article from Iowa State University Forestry Extension (no longer available online) discusses whether or not to stake a tree:

“If possible, avoid staking and/or guying trees. Small trees, trees less than six feet tall or less than one inch in caliper or diameter, should not need staking to support them. As tree planting stock gets larger, their root system, ball-and-burlap, or pot size may not be sufficient to support them without tipping or transferring top movement down to the root system. With trees that may be able to support themselves, plant them and watch the planting hole for several days after planting. If the tree tips or leans, it needs support; if the plant stem at the soil line is moving excessively, creating a ‘crowbar’ hole which is a quarter of an inch or larger than the stem of the tree, it probably needs support.”

The book The Tree Doctor by Daniel and Erin Prendergast (Firefly Books, 2017) says that staking might be needed if your newly planted tree is in a windy or exposed location. The authors recommend anchoring the tree with at least two stakes at equal distance from the trunk. Drive the stakes into solid, undisturbed ground at least 2 feet deep, and tie the tree with biodegradable material like burlap, rather than wire encased in rubber hose. Leave at least an inch of room between each tie and the tree trunk. The tree should be able to sway in the wind. Remove the stakes and ties after a year.
I also wonder if you could carefully dig down and shift the position of the tree in its planting hole to guide it upright. If you are able to do this easily, you can avoid staking.

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Overwintering Ensete ventricosum

I recently purchased an Ensete ventricosum, which I will plant in a large
container. I live in Bellevue. Should I consider this
plant an annual only? Or is there a way I can overwinter the plant, so that I can enjoy it next year? I don’t have a green house. Would it work to bring it into the garage? If I bring a potted plant into the garage, doesn’t it need water and light? Or could I put hay over the container and leave it outside?

 

I could not find any information that suggested overwintering this particular
plant outside would be successful. In Bellevue, some other species can be
overwintered outdoors, like Musa basjoo, but E. ventricosum is more tender.

Fortunately, I did find several resources about overwintering your plant
indoors, so you may be able to enjoy your plant over several seasons. The
Missouri Botanical Garden information suggests several methods for overwintering
E. ventricosum. Here is an excerpt:

 

  1. Bring container plant indoors in fall before first frost and place container
    in a large sunny room for overwintering as a houseplant, with reduced water and
    fertilization;
  2. If container plant is too large to bring inside as a houseplant, cut foliage
    back to 6-8″ in fall after first frost, and store container in a cool, dark,
    frost-free corner of the basement until spring, with periodic addition of a
    touch of moisture as needed in winter to prevent the soils from totally drying
    out;
  3. If container plant is too heavy or too large to bring inside, remove
    plant from container in fall before first frost, wrap roots in plastic and store
    in a cool, dark, frost-free corner of the basement until spring (foliage may be
    trimmed back or left on the plant and allowed to brown up in the normal course)

 

If you don’t want your E. ventricosum as a houseplant, overwintering in the
garage seems possible. Given that the Missouri Botanical Garden recommends a
basement and the plant will be basically dormant, meaning it will not want much
water or light, your garage will probably be fine as long as it is warm enough.

The Royal Horticultural Society suggests growing it in a sheltered spot outside, or overwintering it in a well-ventilated temperate greenhouse. Another RHS page no longer available online makes these recommendations about temperature:

To overwinter Ensete, our glasshouse is kept at 16 C (61F) by day and 12C
(53 F) at night – at lower temperatures, lifted plants are prone to rotting. The
lower the overwintering temperature, the earlier Ensete should be lifted and
established in their winter containers, and the drier they should be kept
subsequently.

The site of Cool Tropical Plants includes an illustrated tutorial of lifting Ensete for the winter, however, simply notes that the minimum temperature should be 3 C (about 37 F).

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Treating peach leaf curl

Have you any advice about how to combat peachtree leaf curl using
natural methods at this stage in the season? I’ve just read about the
use of thyme or oregano oil, but no advice on amount used. I would be
glad of any help!

 

The information I was able to find about thyme oil as a treatment for
Taphrina came from an application to the U.S. Patents Office, so I cannot
speak for its efficacy.

The U.S. Department of Agriculture’s Agricultural Research Service offers
research on the use of plant essential oils in postharvest disease control, too. My impression is that the efficacy of these plant-based oils is still being studied and evaluated.

I also found information on managing peach leaf curl (Taphrina deformans)[formerly available online] from
the National Sustainable Agriculture Information Service which suggests
using lime sulfur, acceptable by U.S. organic standards, though European
standards may differ. Below is a more substantial excerpt:

 

The life-cycle diagram above in Figure 2 shows that the infection period
for leaf curl is when new leaves start emerging from buds in the spring.
Spraying after the buds have opened is ineffective, because infection
takes place as the young leaves emerge, and the fungus develops inside
the leaf.

Accordingly, sprays must be applied during the trees’ dormant
period after the leaves have fallen and before the first budswell in the
spring. Many orchardists spray just prior to budswell during the months
of February and March. Orchards with a history of severe peach leaf curl
benefit from a double application: in the autumn at leaf fall and again
in late winter or early spring just before budswell.

Fortunately for the organic grower, lime sulfur is one of the most effective
fungicides for control of peach leaf curl and is allowed in certified organic
production . Bordeaux and copper fungicides are also approved for certified
organic programs and are effective as well, but not as effective as
lime-sulfur.

Pscheidt and Wittig (6), performed trials comparing Kocide, lime-sulfur,
several synthetic fungicides, and Maxi-Crop seaweed for leaf curl
control. Lime-sulfur and one of the synthetics (ziram) were best, roughly
twice as effective as Kocide. Seaweed sprays, despite positive anecdotal
reports, were completely ineffective.

Severe leaf curl infection can cause the tree to shed many of its leaves
and to replace them with a second flush of growth. At this time the tree
will benefit from a light feeding with a quickly-available soluble
fertilizer such as compost tea or fish emulsion to help it recover.

There are various levels of resistance to leaf curl among varieties;
however, because of the relative ease of controlling the disease,
breeding for resistance has not been a priority. Redhaven, Candor,
Clayton, and Frost are some of the cultivars with resistance to leaf
curl, though none is immune. In contrast, Redskin and cultivars derived
from it are susceptible.

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The City of Seattle’s Integrated Pest Management Solutions pages for
landscaping professionals also suggests methods of prevention and
control. Damage may be reduced by sheltering the tree from winter and
early spring wet. If only a few leaves are affected, they may be removed
by hand. Peach leaf curl does not usually kill the tree, though fruit
yield will be reduced. This resource also mentions using copper
fungicides and lime sulfur when the tree is dormant.

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Growing and caring for Zamioculcas zamiifolia

What are the cultural requirements for Zamioculcas?

 

Zamioculcas is in the plant family Araceae, and its common name is the Aroid palm. According to the Sunset Western Garden Book (2007), this tropical African perennial which resembles a cycad or a palm will grow slowly to 4-5 feet high by 3-4 feet wide. Grown outdoors, it prefers partial to full shade, but indoors you should provide bright filtered light. It should be placed on a tray of moistened pebbles, and misted occasionally. During active growth, keep the soil evenly moist, and give it balanced fertilizer once a month. During the fall and winter months, do not fertilize, and only water when the top inch of soil becomes dry. In summer, the plant may be moved outside to a shady spot. All parts of this plant are poisonous.

You can find discussion among growers of Zamioculcas zamiifolia (sometimes called “the ZZ plant”) on the University of British Columbia Botanical Garden Forum.

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Planting bare root roses

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).

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Winter watering

Can you tell me, what’s the deal with watering in winter? I’ve heard that foundation plants which don’t catch the rain under the eaves must be watered even in wintertime. Someone else says that watering anything in winter subjects it to freezing.

Now I’m in a quandary. I don’t want my plants to freeze to death, nor do I want them to die of dehydration. So what’s the answer?

 

According to Colorado State University Extension, you do need to water if there has not been snow or rain. You should water when the temperature is above freezing and the soil is not frozen. You should water early in the day so that the water can soak in before it gets cold overnight and freezes.

Here in the Puget Sound area we do not have freezing temperatures very often so you should go ahead and water, especially those plants under the eaves.

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On propagating Paulownia

How can I propagate a Paulownia tree?

 

Something to consider before propagating this tree is its invasive potential. Depending on your location, increasing the population of Paulownia trees may not be wise. The U.S. Department of Agriculture lists Paulownia tomentosa as an invasive species. If you are in King County in Washington State, you may be interested to know that the Center for Invasive Species shows this tree in its Early Detection and Distribution map.

Nevertheless, directions for propagation are available. Peter Thompson’s book, Creative Propagation (2nd edition, Timber Press, 2005), states that Paulownia is best propagated by seed in the spring, or by semi-mature root cuttings laid horizontally just below the surface of the soil. I suggest that you think twice before propagating this tree.

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Growing Epimedium

Can you recommend some Epimedium species and tell me what kind of conditions they prefer?

 

The resources I consulted say that most Epimedium species prefer part shade, and most are evergreen. Some will tolerate a partly sunny site as long as the soil does not dry out.

Epimedium perralderianum has bronze leaves that turn green and last throughout the year. It blooms in March/April.

Epimedium x rubrum prefers shade, so if your site is partly sunny, this might not be the ideal choice.

Collectors Nursery in Battleground, WA, also carries several varieties.

One gardening website, Paghat’s Garden, has especially good information.
The site developer recommends in particular the following varieties:
Epimedium x versicolor ‘Sulphureum’, or Yellow Epimedium – for its evergreen foliage
Epimedium grandiflorum ‘Lilafee’ – for quite striking lavender flowers and evergreen foliage

Richie Steffen, curator of the Elisabeth C. Miller Garden, is the author of “Epimediums” Queens of the Woodland” published in Pacific Horticulture, April 2008.

A recent book, The Plant Lover’s Guide to Epimediums by Sally Gregson, has excellent illustrations as well as information.

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