best soil conditions for growing bunchberry

What are the best soil conditions for bunchberry, Cornus canadensis?

In his book, Gardening with Native Plants of the Pacific Northwest (University of Washington Press, 1996) Arthur Kruckeberg talks about “an acid, gritty soil, somewhat damp.” Paghat’s Garden, a local gardener’s web page, says that “being near rotting deadfall helps bunchberry a great deal, as it is frequently found growing naturally around rotting stumps and logs. To meet its desire for rotting wood in its vicinity, I started it in soil into which I had buried many whole twigs before planting the bunchberries, and I worked deeply into the soil a considerable amount of wood shavings in which our pet rats had pooped, besides organic matter from finished compost. After it is established it is a good idea to mulch every two or three years with pine or fir needles gathered from the woodlands. The wood particles worked into the soil seem really to do the trick and we’ve experienced none of the troubles some people have when attempting to establish a healthy patch of bunchberry. After a couple years, shavings or woodchips will have broken down into good organic compost, so to keep the quotient of decaying wood current, every couple years I pound a few sticks (mostly sundry bush trimmings) flush into the soil, as I also do for huckleberries and other such plants that have a strong symbiotic relationship with the sorts of beneficial fungus that break down wood.”

on amending heavy clay soils

Part of my yard has clay close to the surface. In addition to heavy and yearly amending with compost and other organic materials, I have heard that adding gypsum is helpful for breaking up heavy clay. Any thoughts or suggestions on this?

One of the most reliable resources I’ve found on how to amend soil is Prof. Linda Chalker-Scott, of Washington State University Extension. According to her very useful website on horticultural myths, gypsum does improve clay soil but is not the best choice for most home gardens. Here is an excerpt:

“With the exception of arid and coastal regions (where soil salts are high) and the southeastern United States (where heavy clay soils are common), gypsum amendment is just not necessary in non-agricultural areas. Urban soils are generally amalgamations of subsoils, native and non-native topsoils, and–in home landscapes–high levels of organic and non-organic chemical additives. They are also heavily compacted and layered (and gypsum does not work well on layered soils). In such landscapes, it is pointless to add
yet more chemicals in the form of gypsum unless you need to increase soil calcium levels. This nutrient deficiency can be quickly identified by any soil testing laboratory for less than a bag of gypsum costs. (If you need to improve sulfur nutrition, it’s wiser to use ammonium sulfate). To reduce compaction and improve aeration in nearly any landscape, application of an organic mulch is more economically and environmentally sustainable.”

Colorado State University in an article (now archived) says the following about gypsum as a soil additive:

“The belief persists that adding gypsum can ‘break up’ […] compact clay soils […] Calcium sulfate or gypsum when added to our clay soils only increases the already high calcium content. Since plants growing in our soils already have all the calcium they need, the added gypsum does nothing to improve plant growth. Spending money and time to add gypsum to a soil that is already high in calcium is a waste of money and effort.

“As far as relieving soil compaction, gypsum has no effect. Loosening soils is a physical process, not a chemical one. The way to break up tight, clay soils is through adding and mixing in organic amendments. The amendment holds the clay particles apart creating more space for the air so critical to plant root growth.”

It sounds to me as if your practice of amending the soil with compost and organic matter is the best approach.

Trumpet Vine and vines that attract hummingbirds

I live in Bellevue and was thinking of planting a couple of Trumpet vines against a very tall wood fence in my yard (Campsis radicans). I found quite a lot of messages online about these plants being very invasive. Do you know that to be true for this area? If so, what other plants could I use against the fence and which attract hummingbirds as the Trumpet Vine claims to do.

Campsis radicans (trumpet vine) is not considered officially invasive in the Pacific Northwest, though it may be an aggressive grower that needs (or takes up) a fair amount of space. If you do decide to look for alternative vines to grow, scarlet runner bean is attractive to hummingbirds, as are honeysuckle (harder to grow than Campsis as it has occasional problems with aphids), and clematis, according to Naturescaping, published by the Oregon Department of Fish and Wildlife (2001).

The local website of Rainyside Gardeners has a list of nectar plants for Northwest hummingbirds. Of the plants on this list (which includes Campsis radicans, Honeysuckle(Lonicera), and Scarlet runner bean), Eccremocarpus scaber, Ipomoea, Jasminum stephanense, Mina lobata, and Tropaeolum are all vines, some of which are annual.

King County Natural Resources has a searchable native plant guide, and here are the native plants they recommend for hummingbirds:

Tree:
- Madrone; madrona (Arbutus menziesii)
Vine:
- Orange honeysuckle (Lonicera ciliosa)
Shrub:
- Red-flowering currant (Ribes sanguineum)
- Black gooseberry (Ribes lacustre)
Groundcover:
- Thrift; sea pink (Armeria maritima)
- Western columbine (Aquilegia formosa)
- Cooley’s hedge nettle (Stachys cooleyae)

In my own garden, the Italian Jasmine (Jasminum humile, a shrub grown against a wall, not a vine) appeals to hummingbirds, and in the fall they seem to like the Camellia sasanqua.

encouraging flower growth on gooseneck loosestrife

I was very excited to plant some gooseneck loosestrife in my garden but it has proven to be a dismal failure. It’s been three years and the plant is refusing to “gooseneck”. Instead, it gives me very frail flowers, reaching straight up and lasting a very short time. I’m at the point of pulling it all out, but wanted to see if there was any way to encourage it to offer up some healthy, bobbing white flowers.

What are the conditions where the gooseneck loosestrife (Lysimachia clethroides) is planted? This plant tolerates
partial shade to full sun. The fact that yours is growing straight up makes me wonder if it is in too much shade and is striving for more light. Usually, this is a vigorous plant (sometimes exceedingly so–it can become invasive), so other things to consider are soil conditions (prefers well-drained soil with a lot of organic matter), and moisture. If planted in full sun, loosestrife will need sufficient water to thrive.

It is possible, too, that after 3 years, your plant needs to be dug up and divided. This might help give it renewed vigor. Propagation information from the Iowa State University Extension suggests that “Perennials such as gooseneck loosestrife (Lysimachia clethroides)… may be divided every 3-5 years to improve plant health.”

Other good sources of information about this plant are Cornell, and the Kemper Center for Home Gardening.

plants for screening

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.

on the use of Epsom salts in the garden

Are Epsom salts good for outdoor garden plants (trees, perennials, evergreens, deciduous etc)? If so, how much & when do I use the Epsom salts? Please let me know which plants would benefit from this solution.

The best information I found on the use of Epsom salts in the garden comes from horticulture professor Linda Chalker-Scott of Washington State University. Epsom salts are also known as magnesium sulfate, and the theory (or the myth, according to Chalker-Scott) is that adding this substance to the soil provides necessary nutrients to plants, and improves their growth. The reality is more complicated, and she ultimately recommends that home gardeners not use Epsom salts, as they tend only to be useful in intensive crop production (such as farming) where there is a known lack of magnesium.

Rather than use Epsom salts, you might simply make a practice of amending your garden soil regularly with compost. WSU lists some of the many benefits of using compost.

Seattle Public Utilities also has information on growing healthy soil and composting.

on the safety of using horticultural oils on edible plants

I have some insects on my bay laurel, which we use for seasoning. Someone told me to spray it with horticultural oil. I wondered, though, if it would still be safe to use the leaves in cooking. Is horticultural oil petroleum based?

As you suspected, horticultural oil is petroleum-based. U.C.Davis provides information on Integrated Pest Management for the plant I am assuming you mean, the usual source of culinary bay leaves, sometimes called sweetbay, or Laurus nobilis. (Just to be clear, I don’t think you are referring to the plant known as California bay laurel, Umbellularia californica, which has leaves that are aromatic and reportedly edible, but not commonly used for seasoning.)

They also note that “…specially refined petroleum products, often called narrow-range, superior, or supreme oils. Some botanical (plant-derived) oils are also available.”

When referring to plant-derived oils, I believe they are referring to Neem oil, as described in this information from U.C. Davis Integrated Pest Management. Additional information from the Cornell University Resource Guide for Organic Inesct and Disease Management about Neem and human health is excerpted here:

Studies of azadirachtin mutagenicity and acute toxicity have shown that it likely does not pose a significant risk to human health. However, some people have exhibited skin and mucous membrane irritation from neem seed dust (Weinzierl and Henn 1991). Note that most studies have been done on azadirachtin, and may not show the
effects of a whole neem product. Neem is used in some commercial human hygiene products.

Another long excerpt on horticultural oil from Colorado State University Extension suggests the following:

Essentially all commercially available horticultural oils […] are refined petroleum products also known as mineral oils. Impurities in the oil that are associated with plant injury, such as aromatic compounds and compounds containing sulfur, nitrogen or oxygen, are removed. Filtration, distillation and dewaxing complete the production of the finished base oil. Final formulations of horticultural oils are normally combined with an emulsifying agent that allows the oil to mix with water. This mixture usually is used at about a 2 percent dilution.

Vegetable oils also can be used as insecticides, although the type of oil can greatly affect its activity. Cottonseed oil is generally considered the most insecticidal of the vegetable oils. Soybean oil, the most commonly available vegetable oil used in cooking, has often provided fair to good control of some insects and mites.

Extracts from seeds of the neem tree, Azadirachta indica, have recently attracted attention as a source of pest management products. Several neem-derived insecticides have been developed. A number of compounds found in neem seeds, notably azadirachtin, have proven useful as insecticides. However, the oil fraction of neem seed extracts, which is mostly free of azadirachtin and related terpenoid compounds, also has demonstrated effects as a fungicide and insecticide. At least one product currently on the market, TrilogyR, consists of a largely azadirachtin-free oil fraction of neem seed extracts. It is formulated with an emulsifier and mixed with water at a concentration similar to horticultural oils (0.5 to 2.0 percent). Many over-the-counter products sold in nurseries that mention neem contain the oils of neem seed extracts.

If you know the insect on your bay tree, Peaceful Valley Farm Supply is one commercial supplier which carries less toxic, of not organic, products to control specific pests. That does not necessarily mean they are safe enough to spray on leaves which will be harvested for cooking.

on pruning lamb’s ear and Himalayan honeysuckle

I have a question about cutting back plants. I have some non-flowering lamb’s ear that is looking quite scraggly. How far back do I cut these, and when?

Also, how far back should I cut my Himalayan honeysuckle? We planted it 2 years ago, and last summer it got 5 feet high!

Also, last year my Hebe plants did not flower. We have Hebe anomala purpurea ‘Nana’. I have recently checked the tags they came with, and it doesn’t mention that it flowers. Is this a non-flowering Hebe? Although the shrubs are lovely, I was hoping for the type that flowers. If we decide to move them, when would be the best time to transplant them?

Yes, Stachys (lamb’s ears) can look pretty ragged after winter. I’m guessing you are growing Stachys byzantina ‘Silver Carpet’ or a similar cultivar, which doesn’t flower. If you look closely, you should see signs of new growth. I would suggest cutting back all the tattered or dried leaves as far as you are able, without injuring new growth. March is a good time to divide the plant if you like. (I have shared this plant many times and moved clumps to new locations. It is quite tough, and will transplant easily.)

Himalayan honeysuckle, Leycesteria formosa, can be cut back to the ground (or within a few inches of the ground) in late winter or early spring,according to Sunset Western Garden Book. The website of Rainyside Gardeners (a Northwest site) has a useful page on Leycesteria formosa.

According to Hebes: A Guide to Species, Hybrids, and Allied Genera by Lawrie Metcalf (Timber Press, 2006), Hebe anomala ‘Purpurea’ is a synonym for Hebe odora ‘Purpurea’ which is supposed to have a lot of flowers. He doesn’t mention the dwarf variety, ‘Nana,’ but I assume it would have similar attributes. Even with the nomenclature confusion, there seems to be some consensus about the floriferous qualities of the plant: Douglas Chalk’s Hebes & Parahebes (Christopher Helm, 1988) lists Hebe ‘Anomala’ as a cultivar of Hebe odora, and he too says it has lots of flowers. Are your Hebes getting enough sun? Some Hebes will flower in partly shady sites, but the flowering will be diminished. Could they have been pruned accidentally, just before flowering? Another possibility is that the plants are not mature enough to flower. The Metcalf book mentions a few species which can take years to produce flowers. He also says that flowers are enhanced by chilling followed by warmth, over a period of about 12 weeks. The number of hours of daylight to which the plants are exposed is also a factor. As far as transplanting, doing it in March should be fine. It isn’t too hot, and we are likely to have the occasional rain,but you should still water well when you first move them.

propagating sedums and succulents

I am learning how to propagate plants for my yard. I am now into Sedums and other succulents. I am trying to learn how to propagate Echeveria x hybrida “The Rose.” This one has me totally baffled. Can you help?

First, here is some general information. The propagation method you choose for Sedum depends on the habit of the plant, according to the American Horticultural Society’s Plant Propagation (edited by Alan Toogood; DK Publishing, 1999). Most species will root easily from cuttings in 1 to 6 weeks.

Tender species can be propagated from leaf cuttings. Take leaves off a stem. Place on damp newspaper in bright shade at 61 degrees F. Roots and plantlets should form in 3 to 4 weeks. You can also use stem cuttings by taking 2 to 3 inches from the tip of a stem and allowing the cutting to callus for a day. With hardier forms of Sedum, use 3/4 to 1 1/4 inch stem cuttings.

The book Echeveria Cultivars by Lorraine Schulz and Attila Kapitany (Schulz Publishing, 2005) offers directions on propagating from offsets, cuttings, cuttings from crests, head cuttings, leaf and stalk cuttings, and seed.

proper time to prune Arbutus unedo and other plants

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 reticulata is not a common tree, nor are the species of Viburnum and Osmanthus you are growing. Unless there are compelling reasons to prune harder, I would suggest sticking to the 3 D’s of pruning: take out only dead, diseased, and disordered branches. Another general rule of thumb is never to remove more than 1/3 of the plant at one time. You might want to consult a certified arborist as well. You can find arborists through Plant Amnesty’s referral service or the Pacific Northwest Chapter of the International Society of Arboriculture.