best time to prune Pieris

I have a Valley Rose Pieris which has finished blooming. I wanted to trim it, but noticed that it has small green buds on the branches. What would be a good time to trim this plant?

The best time to prune Pieris is in the spring when it is done flowering. You can prune it to the shape you desire. It grows new shoots readily from old wood, according to Peter McHoy’s Pruning: A Practical Guide (Abbeville Press, 1993). There are more detailed guidelines in Cass Turnbull’s Guide to Pruning (Sasquatch, 2006). She says you can remove up to a quarter of live foliage without endangering the plant. Always remove dead, diseased, or awkward growth first. She recommends thinning out branches which are too straight, too skinny, or wander too far. Working from the inside of the shrub outward, your goal would be to make the growth less crowded. Pieris also responds to being “limbed up” and treated like a tree, with lower branches removed, if that is a shape you prefer.

common ailments affecting rhododendrons

My rhodies have black spot, rust. Is there a plant medicine I can put in the soil so it will get absorbed by the entire plant rather than spraying every other leaf.

I am sorry to hear about your sick Rhododendrons. You should take a take a leaf sample into a Master Gardener clinic for (free) diagnosis. I have linked a list of clinics in Snohomish County below. Their volunteers are trained in identifying plant diseases and suggesting solutions.

If you cannot get into a clinic try the HortSense webpage from Washington State University Cooperative Extension, and search the common ailments affecting rhododendrons (in the Ornamental Shrubs section).

The reason why it is vital to get an accurate diagnosis is because some fungal diseases do not have treatments that really work, such as rust, while other “leaf spot problems” are not caused by fungus at all, therefore spraying with fungicides or applying a systemic to the soil would only be a waste of time and money!

Try contacting the Snohomish County Master Gardener Clinics to see if you can bring in samples.

causes for daffodil lack of blooms

I’m having a problem with my daffodils. They came up, but very few of them are blooming. This is the third year for them, and the worst turn out. They seem to be turning yellow at the bottom of the plant. They have multiplied well, and came up looking fine. Several of my friends are having the same problem. Could it be because they had so many days of below freezing weather this winter?

We found a helpful article from the American Daffodil Society. Potential causes for a lack of flowers include lack of fertilizer, too much nitrogen fertilizer, shade, competition with other plants, poor drainage, virus, foliage cut off too soon, need to be divided, or weather stress (such as early extreme heat) in the spring.

The cold weather should not have been a problem provided the bulbs were planted deep enough.

more about Persicaria

I have a something called Chevron Plant in my yard. There is a distinct v-shape pattern on the upper side of the leaf, and it gets red tiny flowers in the spring/summer time. It grew about 1.2 in height. Can you tell more about this plant?

Chevron Plant is not a known common name, but the perennial Persicaria virginiana (and its cultivars) is notable for the chevron-shaped markings on its leaves. A more familiar common name is Knotweed (and it is in the same family as the invasive Japanese knotweed, sharing some of that plant’s tendency to spread). The genus includes 50-80 species of annuals and perennials, often rhizomatous (spreading by roots) or stonoliferous (spreading by runners). They may be evergreen, semi-evergreen, or deciduous. There are several varieties with interesting v-shaped leaf patterns, and some have red flowers. To verify whether this is what you have, try searching the plant’s botanical name on Google or another search engine and then click on Images and search for Persicaria.

If that is correct, they are best grown in any moist soil in full sun to part shade. If they get out of control they can be cut to the ground in late fall or winter. Some species can be aggressive and even officially invasive and need to be controlled.

If that is NOT your plant, the Hyde Herbarium at the Center for Urban Horticulture can provide a positive identification.

There may be people at your local nursery who can help you as well.

on determining tree injury types

How can I find out if my Monkey Puzzle tree was poisoned by my neighbors? I found 6 holes drilled into it on their side.

Before assuming the tree has been poisoned, make sure that the holes were not actually caused by woodpeckers or flickers, since this is common behavior among such birds–and less common behavior among neighbors, one would hope!

In order to determine for sure whether your trees have been poisoned, you may wish to consider contacting a certified arborist. For a fee, an arborist will visit your property and make a diagnosis or recommend another plan of action.

For a list of arborists, contact Plant Amnesty, an organization of arborists and vetted gardeners at 206-783-9813 or visit the Pacific Northwest Chapter of the International Society of Arboriculture.

To pursue a legal solution to the problem contact the King County Law Library where County law librarians will be happy to help you with your research.

The book Neighbor Law by Emily Doskow and Lina Guillen (Nolo Press, 2014) is also a useful resource.

diseases affecting Hawthorn trees

My Hawthorn tree has black spots on the leaves. Can you tell me what disease this might be? In general, what diseases affect Hawthorn trees?

To learn about diseases most common to Hawthorns in the Pacific Northwest, visit the Pacific Northwest Plant Disease Management Handbook and search on the word hawthorn. You will get a list of several diseases that commonly affect hawthorns; click on any of them for a full explanation.

on transplanting bamboo

I transplanted some bamboo and now some of it is dying. Can you give me some information on how to transplant bamboo correctly?

The following is an excerpt from the (now archived) American Bamboo Society webpage.

Q. How do I transplant part of a large clump of bamboo?

Transplanting is hard work and involves digging a large chunk of root ball out of the ground. Never transplant bamboo when it is shooting. Dig bamboo either very early in the spring before there’s any chance of shooting or wait for the growth period to be over late in the autumn. You should look for a clump of culms that has come up in the last year or so and which includes at least three or four healthy-looking culms. A good size for the clump would be at least two feet in diameter. Bamboo roots (rhizomes) are tough but must not be allowed to dry out even for a few minutes. You may have to use a very sharp shovel, ax or saw to separate the roots from the rest of the grove. If you will be transferring the division by truck, then water the leaves and roots well, wrap the whole thing in plastic and get it into the ground as quickly as possible.

diseases and pests affecting fava beans

I have small ants on my fava beans and it appears that some of the young pods are blackening. Do ants eat fava beans? Is there anything I can do this year, or should I just start over next time in a different location?

The ants may be visiting the extrafloral nectaries of your fava bean plants! (see this photo of just this activity)

Apparently, some insects are attracted to the nectar of Vicia faba, according to Oregon State University Extension:

“Many beneficial insects, including predatory wasps and lady beetles, are attracted to the nectar of flowering fava bean.

“Fava bean also has extrafloral nectaries on its stipules, the leaf-like structures at the base of the leaf petioles. Extrafloral nectar is available to short-tongued insects that do not have access to the nectar of the legume flowers. Both beneficial and pest insects (e.g., lygus bug) feed on extrafloral nectar.

“Fava bean is susceptible to aphid damage, especially from the bean aphid. Although aphids usually do not affect fava bean’s utility as a cover crop, they can cause considerable damage to the seed. Broadbean weevils also can reduce seed yields.”

Here is similar information, from Golden Gate Gardener.

It’s possible that the blackening is from aphid honeydew, or perhaps it could be chocolate spot, which is a fungal disease (Botrytis fabae). Here is more about this, from the Royal Horticultural Society.

Practicing crop rotation might be beneficial with your favas as it is with other edible plants. Below is additional information on vegetable crop rotation.
Washington State University Extension: Using Crop Rotation in Home Vegetable Gardens

To check your favas for botrytis or other diseases, take samples to a Master Gardener Clinic for diagnosis.

gooseberries and powdery mildew

We purchased a gooseberry last year. It got powdery mildew and lost its leaves. This spring it came back with lush leaf growth and has not had the mildew, but it has brown spots that just developed. Some leaves are turning completely brown. Any suggestions?
On the east coast in NY we had huge prolific berried bushes that didn’t seem to have any of the problems we are having here in Snohomish County.

Powdery mildew is certainly a known problem for gooseberries here, but there are other diseases that show up as spotting on the leaves. The Royal Horticultural Society describes mildew on gooseberries. Cornell University’s Department of Horticulture has a guide to currants and gooseberries which describes several other problems affecting the leaves of these plants.

We can’t diagnose the problem remotely, but compare your plant’s symptoms with this information about anthracnose from Washington State University’s HortSense website:

“Anthracnose is a fungal disease affecting the leaves of currants and gooseberries. Leaves show small, round or irregularly-shaped spots on the upper or lower surfaces. The spots are usually dark brown in color and may develop tiny, gray fungal structures in the centers. Severely affected leaves may turn yellow and drop prematurely. The leaf loss can weaken plants and reduce yields. Currant fruit may also show spotting. On fruit, the spots are tiny and resemble flyspecks. Severely infected berries crack open and drop. The fungus is spread from infected to healthy leaves by splashing water and overwinters in fallen leaves. Disease development is favored by wet spring weather.
Avoid overhead watering.
Rake fallen leaves from beneath plants. Destroy or discard (do not compost) diseased plant materials. Cultivation to bury diseased leaves may also be effective.
Space plantings and prune to provide good air circulation and reduce humidity.”

It would be worth having a your local county extension agent test the affected foliage before you attempt to treat the problem.

Just as an aside, gooseberries do well in areas that have good winter chilling and humid summers, which sounds more like parts of the East Coast than our winter wet/summer dry Northwest. The website of California Rare Fruit Growers describes the native ranges of gooseberries:

“Gooseberries are derived mostly from two species: the European gooseberry (Ribes grossularia), native to the Caucasus Mountains and North Africa; and the American gooseberry (R. hirtellum), native to northeastern and north-central United States and adjacent parts of Canada. So-called European cultivars are pure species, but virtually all so-call American cultivars also have European genes.

more about soil-based potting mixes

I am doing container gardening — rather large plantings that will incorporate small trees and shrubs — and therefore want a potting mix that will last longer than the usual for smaller containers, and will provide some nutrients. I just read about soil-based potting mix, but there is no further info in my text. Can you describe this, and tell me if it commercially available, or do gardeners mix up their own recipe?

There are a variety of opinions about soil-based potting mix. Taylor’s Guide to Container Gardening (edited by Roger Holmes, Houghton Mifflin, 1995) provides a recipe for a “real soil” mix combining equal parts garden loam, compost or peat moss, and coarse sand. The sand should be as coarse as possible, and should not be able to pass through a window screen. According to the guide, “the success of any mix using soil depends on the soil’s quality.” For large pots and planters, the mix should be equal parts coarse, medium, and fine materials (from Landscaping with Container Plants, by Jim Wilson, Houghton Mifflin, 1990), for example:

Coarse material: small nuggets of pine or fir bark

Medium material: pulverized pine or fir bark

Fine material: moistened sphagnum peat moss

Extension.org has information on organic potting mixes. ATTRA Sustainable Agriculture Program has additional information

Mother Earth News published an article by Barbara Pleasant in the December 2008/January 2009 issue entitled Make Your Own Potting Soil which should be helpful. The recipe includes pasteurized compost or soil.