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Plant Answer Line Question

Keywords: Berberis, Skimmia, Leucothoe, Fatsia, Euonymus, Elaeagnus, Shade-tolerant plants, Osmanthus, Aucuba, Viburnum, Shrubs, Prunus, Camellia, Buxus

Can you suggest some shade shrubs/low trees that could be used in the bottom quarter of a huge, years-old pile of yardwaste and branches that is now a 20 foot cliff? I have started with some vinca minor in the lower part but could use some ideas of some things to plant that might get 15 feet tall, evergreen, and grow in woods/shade or sun through trees.


The closest list I could find to meet your needs is one of evergreen shrubs that will grow in shade:

Japanese aucuba - Aucuba japonica vars.
common boxwood - Buxus sempervirens
camellia - Camellia sp.
gilt edge silverberry - Elaeagnus x ebbingei 'Gilt Edge'
Euonymus - Euonymus fortunei radicans
Japanese aralia - Fatsia japonica
drooping Leucothoe - Leucothoe fontanesiana
Oregon grape - Mahonia aquifolium
Burmese mahonia - Mahonia lomariifolia
longleaf mahonia - Mahonia nervosa
holly leaf osmanthus - Osmanthus heterophyllus vars.
English laurel - Prunus laurocerasus 'Mount Vernon'
Japanese skimmia - Skimmia japonica
evergreen huckleberry - Vaccinium ovatum
nannyberry - Viburnum lentago

Source: The Pacific Northwest Gardener's Book of Lists, by R. & J. McNeilan, 1997, p. 46-47

Date 2019-09-19
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Plant Answer Line Question

Keywords: Viburnum, Integrated pest management, Aphids

I have a small snowball bush that I planted three years ago. Each spring this plant is inundated with more and more ants and aphids. I try to garden organically and could use Safer Soap on it, but it is large and the leaves are all curled under and withering from the insects. Is there anything other than Safer Soap that I could use to help the plant, either systemic or otherwise?


Following are the best sources I have found about environmentally friendly control of aphids.

Aphids (order Homoptera)

Almost all plants have an aphid species that may occasionally feed on them. Many aphid species attack several plants rather than having only one host. Trees (esp. birch, beech, maple, apple, peach, apple, plum, cherry, spruce, dogwood, willow); annuals (esp. nasturtium, snapdragon); perennials (esp. lupine, roses, lilies, begonias, columbine); vegetables (esp. peas, beans, brassicas, lettuce, spinach); fruit (esp. apple, peach, cherry).

Small (2 mm long), pear-shaped, softbodied insects in a range of colors (green, brown, red, yellow, black). Most are wingless, but winged aphids appear at certain times, especially when populations are high or during spring or fall. A few species appear waxy or woolly. A magnifying glass will reveal the long, slender mouth parts used to suck plant fluids. Aphids are usually found in clusters, especially on new growth. Signs of aphid infestations include sticky honeydew on leaves or under plants, distortion of leaves, stunting of shoots, or large numbers of ants on the plant.

Life Cycle:
Overwintered eggs of some common garden species hatch in spring. These wingless females reproduce asexually, bearing live young (up to 80 per week) that already have the next generation developing inside. Young aphids, called nymphs, molt four times before becoming adults. There is no pupal stage. This simple, rapid reproduction allows for very large population increases in a short time. Late in fall, males and females are produced, mate, and the females subsequently lay eggs. Winged aphids may appear at certain times, allowing the colony to move to other locations. Not all aphid types have this reproductive pattern, but many do.

Natural Enemies:
Aphids have many natural enemies, including birds, spiders, ladybird beetles, lacewings, syrphid fly larvae, and braconid wasps. A naturally occurring fungal disease can also kill aphids when conditions are right. Ants have a symbiotic relationship with aphids: ants milk the aphids for honeydew while protecting the aphids from natural enemies.

Check plants often, since aphid populations can rise rapidly. Inspect growing tips and undersides of leaves. On trees, clip off leaves from several parts of the tree to look for aphids. If you see large numbers of ants on tree trunks, check for aphids on limbs and leaves. Look also for associated signs, such as yellowed leaves, stunted or distorted growth, or dripping honeydew. Sticky traps can be used to monitor for winged aphids. Check for signs of predators (named under Natural Enemies above), aphids that have been parasitized (look for a small exit hole on a dead, brown aphid body), or that have been killed by disease. Substantial numbers of any of these natural control factors can mean that population numbers will fall rapidly without the need for treatment. Because of the rapid changes that can occur in aphid populations, it is important to record monitoring data to detect changes due to predators or treatments.

Action Threshold:
Due to the incredibly high numbers that may be present, counting individual aphids is usually not practical. Action thresholds can be based on general descriptions of aphid density, plant damage such as stunted or distorted growth, or unacceptable amounts of honeydew beneath trees. Treatment should be triggered by rapidly rising numbers, unacceptable plant damage, or by honeydew falling on structures and people. Aphids seldom kill a plant, but they can cause defoliation. They also carry diseases from one plant to another. It is usually not necessary or even desirable to treat at the first sign of aphids, since low populations are needed to sustain predators.

Cultural/Physical Controls:
Plant selection: If possible, avoid or consider replacing varieties such as birch that have ongoing, serious aphid problems. Check transplants for aphids and remove them before planting.

Water spray: A strong blast of water knocks aphids from the plant, and most will not return. Water also helps rinse off the honeydew. Do this early in the day to allow leaves to dry and minimize fungal diseases.

Pruning: Where high aphid populations are localized on a few curled leaves or new shoots, prune these areas out and drop in soapy water to kill the aphids.

Fertilization control: High nitrogen levels favor aphid reproduction. Avoid over-fertilization and use slow-release rather than highly soluble fertilizers.

Sticky or teflon barriers: If you see ants crawling up the trunk of trees or other woody plants, place a band of sticky material (such as Tanglefoot or Stik-Em) around the trunk. Place a protective band of fabric tree wrap or duct tape underneath the barrier first. Teflon tape barriers may also be effective. Prune out branches touching the ground, buildings, or other plants.

Biological Controls:
Since aphids have many natural enemies, biological control usually means protecting these enemies from ants and avoiding broadspectrum pesticides that kill beneficial insects. Recognize that predator populations usually lag behind aphid populations in time. A number of aphid enemies can be purchased for introduction into landscapes. Ladybird beetles, lacewings, and parasitic wasps and flies are all available. Although such introduced predators may not remain where released, some benefit is likely, especially if releases are staggered in time. Many of the natural predators of the aphid are especially attracted to a garden with plants in the Umbelliferae family, such as angelica, sweet cicely, dill, and Queen Anne's lace. The flowers of these plants provide a good food source for insects, especially parasitic wasps, who may stay to prey on some aphids as well.

Chemical Controls:
Insecticidal soap is widely recognized as the least-toxic chemical aphid control. Although its effect is temporary, it can help to bring aphid numbers down so that natural enemies can take care of them. Repeat applications within a few days may be necessary. Soap works only by direct contact with the insects. Be sure to cover both sides of the leaves. Although readily biodegradable, soaps are highly toxic to fish, so avoid runoff or direct application to water. Avoid using when temperature exceeds 90 degrees F.

Oil sprays:
Supreme or superior-type oils will help to kill overwintering aphid eggs on fruit trees if applied as a delayed dormant application in early spring. Although perhaps not justified for aphid control alone, oils can also control other overwintering fruit pests. Oils may, however, kill some beneficial species. Summer weight oils are also available, but they can burn tender leaves when applied in hot sun.

Conventional chemical control:
Foliar applied insecticides (malathion, diazinon, carbaryl, pyrethrin) are broad spectrum and will kill beneficial insects. They should be avoided, especially in home gardens and landscapes. Remember that allowing some aphid population in the garden helps to keep predators available.

ProIPM Integrated Pest Management Solutions for the Landscaping Professional
The Green Gardening Program is a collaborative effort of Seattle Tilth, Washington Toxics Coalition, and WSU Cooperative Extension, King County.
Sponsored by the Seattle Public Utilities in an effort to promote alternatives to lawn and garden chemicals.
Funded by the Local Hazardous Waste Management Program in King County.
Written by Philip Dickey, Graphic Design by Cath Carine, CC Design

Pest description and crop damage:
Aphids are soft-bodied insects that typically feed on leaves and succulent stems. They may vary in color from pale green or reddish to dark or black. Aphids are usually less than 1/8 inch in length.

Feeding damage to the plant is usually minor, although some leaf and shoot distortion can occur if populations are high. Aphids also produce honeydew, a sweet, sticky secretion that collects on plant tissues and encourages growth of a black sooty mold. This can interfere with photosynthesis of the plant. Honeydew is also a nuisance when it falls on decks, cars, or other landscape surfaces. They are a problem in early summer.

Biology and life history:
Most species of aphids have similar life cycles. Aphid females give birth to live offspring all year without mating. When other hosts are not available, aphids live on a wide variety of weeds. Aphids usually are found in colonies on new growth, the underside of leaves, and near flower and fruit clusters. In summer and fall, aphids may produce winged females and, later, winged males. They mate and produce eggs for overwintering, especially in colder climates. Otherwise, adult aphids overwinter on crops, weeds, or trees. There may be as few as 2 or as many as 16 generations each year, depending on the species and climate.

Management & biological control:
Aphids have many natural enemies, including lady beetles, syrphid fly larvae, and green lacewings. Avoid broad-spectrum insecticide applications that would disrupt these controls.

Management & cultural control:
Wash aphids from plants with a strong stream of water or by hand-wiping. Aphid populations tend to be higher in plants that are fertilized liberally with nitrogen and heavily watered, as this produces flushes of succulent growth. Avoid excessive watering, and use slow-release or organic sources of nitrogen. Control ants, which farm aphids and protect them from predators in order to harvest their honeydew.

Management & chemical control (home):
It is important to cover foliage thoroughly, including lower leaf surfaces.
1. Beauveria bassiana
2. horticultural oil
3. insecticidal soap


Date 2019-12-07
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Plant Answer Line Question

Keywords: Viburnum, Skimmia, Quercus, Limonium, Lavandula, Helichrysum, Elaeagnus, Echinops, Dahlia, Cotoneaster, Calluna, Callicarpa, Aster, Alstroemeria, Achillea, Acer

My son and his sweetheart are planning a wedding in Seattle (my hometown) this coming September and would love to use seasonal flowers and greenery. I have not lived in the area for many years and am at a loss. Can you give us some suggestions please?


Here are some of the plants which are available in September:
Achillea (Yarrow)
Alstroemeria (Peruvian lily)
Callicarpa bodinieri (beautyberry)
Cotoneaster (for foliage)
Elaeagnus (foliage)
Hebe (flowers and foliage)
Helichrysum (straw flower)
Acer (Maple: foliage)
Quercus (Oak: foliage)
Limonium (Statice)
Viburnum tinus

Here is a link to the Washington Park Arboretum web page of seasonal highlights.

A great book on flowers by season is A Year Full of Flowers: Fresh Ideas to Bring Flowers into Your Life Every Day by Jim McCann and Julie McCann Mulligan.

Date 2019-11-07
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Plant Answer Line Question

Keywords: Screens, Thuja, Juniperus, Viburnum, Hedges, Ceanothus

I will be having a very overgrown, rarely pruned laurel removed from my back garden. It has been, if a monstrosity, an effective visual screen. The bare area that it leaves is appproximately 40' in length, is atop a rockery, approximately 3' high, and will look up into the neighbor's back hillside, while they peer down at us in dismay. Can you suggest one or several fast growing, shrubby plants or suitable trees that will act as an attractive visual screen? I do not want bamboo.


Here are a few ideas:

Morella californica

Thuja occidentalis 'Smaragd'

Osmanthus delavayi is also a good choice, but it doesn't get quite tall enough--my own hedge, which is pruned at least twice a year, is about 8 feet tall, so if I really let it go, maybe it would be 10-12 feet.

Juniperus scopulorum 'Wichita Blue'

Juniperus virginiana 'Manhattan Blue'

Viburnum tinus

Ceanothus would also be striking, with blue flowers, but you'd need to find the tallest possible species, and they tend to be short lived.

You could plant a mixed hedgerow, which would allow you to include some of the flowering plants you prefer. King Conservation District has more information on hedgerows.

Date 2019-05-16
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Plant Answer Line Question

Keywords: Viburnum

I have a Viburnum x bodnantense, or what looks a lot like one, and it is blooming already, although this year's leaves have not yet fallen off completely. Would the plant benefit from feeding? I have a Miracle-Gro hose-dispenser and bottled feed which is sprayed at 30:1 dilution. Would this help the plant, which may be weakened by early blooming? Would a later feeding help? I am afraid I'll miss the late December blooms this year. Is that true?


It is possible you have Viburnum x bodnantense. The cultivars 'Dawn' and 'Charles Lamont' bloom from late fall through early spring. Thus, the blooms you are seeing are normal, not early, and they should continue through the winter. Here is a link to a local growing guide from Rainyside Gardeners.

I think that feeding your Viburnum with a synthetic chemical fertilizer like Miracle-Gro would not be a good idea. Miracle-Gro will supply more nitrogen than your Viburnum wants, and you might actually encourage leafy growth at the expense of flowers. All your plant really needs is mulching with good organic compost and occasional feeds of alfalfa, fish fertilizer, or manure.

Local garden writer Ann Lovejoy describes how to fertilize trees and shrubs in spring and fall in her book The Handbook of Northwest Gardening (Sasquatch Books, 2004):

"Spring feeds are generally fast-acting, offering rapidly growing plants the nitrogen they need... A feeding mulch of compost can be fortified with fast-acting alfalfa, which will release more nitrogen if used in combination with composted manures. Alfalfa comes in meal or pellets...

"In fall, most plants stop producing fresh top growth... Fall is a good time to feed roots, which continue to stretch and grow underground despite low temperatures. Adding whole fish meal to your compost feeding mulch will fortify growing roots with phosphorus...

"In my own garden I rarely feed plants directly, preferring to feed the soil."

You may find the following comments about Miracle-Gro of interest. I hope this helps, and I hope your Viburnum keeps on flowering!

Date 2019-05-18
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Plant Answer Line Question

Keywords: Arbutus unedo, Pruning shrubs, Osmanthus, Quercus, Viburnum, Pruning trees

When is the proper time to prune Arbutus unedo? How much can be pruned at a given time? Same question for Osmanthus decorus, Viburnum odoratissimum, and Quercus reticulata.


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.

The book Pruning: A Practical Guide by Peter McHoy (Abbeville Press, 1993) says that Osmanthus decorus can be clipped in late summer. If you want to limit its size without clipping, prune back long shoots to points far inside the shrub in late spring or early summer, after flowering. If the plant is overgrown, you can spread this type of pruning over two or three years, but do not do it annually. I am not familiar with this species of Osmanthus, but I do know Osmanthus delavayi, and grow it as a hedge. It is sheared after it flowers, and then probably two more times before winter. I did have to prune the top back quite hard last year, and this did not seem to cause any problems, but O. decorus may have different needs.

I could not find information about Viburnum odoratissimum specifically, but most pruning books have general guidelines for Viburnum species. Unless you do not mind losing the flowers, it is best to prune when flowering is done. If you are growing V. odoratissimum as a tree, then special pruning may be needed. George E. Brown's The Pruning of Trees, Shrubs and Conifers (Timber Press, 2004) says V. odoratissimum is somewhat tender, and may grow best as a standing bush with the protection of a wall, using ties in places to keep it close to the wall. The only pruning he mentions is cutting out older wood after flowering, and tying new growth back to the wall (if you are growing your plant in a site where you can do this).

According to the Peter McHoy book, oaks do not require routine pruning. Brown's book says not to prune oaks between mid-spring and mid-summer, as a means of protecting against oak wilt and beetle infestation. If you must prune, do it in winter.

Quercus reticulataPlant Amnesty's referral service or the Pacific Northwest Chapter of the International Society of Arboriculture.

Date 2019-09-19
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Plant Answer Line Question

Keywords: Morella californica, Arbutus unedo, Trachelospermum, Osmanthus, Native plants--Washington, Screens, Wisteria, Viburnum

A friend asked me about screening two large propane tanks that, unfortunately, have had to be placed in front of their home on Camano Island. She mentioned wisteria to me and I shuddered. I've seen this plant do a lot of damage to trellis and home alike. Can you recommend, instead, an evergreen solution to this problem?


I am not familiar with the size and shape of propane tanks, but perhaps evergreen shrubs might work to screen them. A concern would be the proximity to the house, and any needed clearance for paths, doorways, and windows. I think you are right to avoid Wisteria. Does your friend prefer the idea of planting vines, or would shrubs be acceptable?

Here are a few suggestions for evergreen shrubs, with links from the local web site, Great Plant Picks:

Some good information is also available about plants for screening (from Virginia Cooperative Extension) and vines, especially evergreen vines such as Trachelospermum jasminoides, which might be a good solution. Local garden writer Valerie Easton on has written helpfully about hedges, as well.

Date 2019-09-19
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