toxicity of elm wood

Can the sap from an elm tree be poisonous to humans? The power company recently cut down an old elm in my garden and I brushed my hand against the stump and got a splinter.

Within about twenty minutes my hand was swollen at least twice its normal size, was very painful, quite hot to the touch and itching like crazy. I ended up in the emergency room, and had to take antibiotics, but the doctor never indicated whether the extreme reaction had anything specifically to do with the type of tree.

We have an older book on plant-induced dermatitis, Botanical Dermatology by Mitchell and Rook (Greengrass, 1979) which includes elm among the trees which can cause “woodcutter’s eczema.” However, it may not be the sap of the tree itself which is the problem, but perhaps the lichens and liverworts which may be growing on the tree (some of which contain usnic acid and other substances which irritate human skin). Here is an abstract of an article which describes this:
Frullania liverwort phytodermatitis

If one were to saw elm wood which was covered in lichen or liverwort, the dust could be an irritant. You may have gotten a splinter which had dust on it. I’m not a medical professional, so I couldn’t say with any authority what may have happened. However, a splinter of any kind can cause inflammation, and if you happen to be especially sensitive to a particular substance, whether it is the wood or sap of the elm, or traces of dust from lichens and liverworts that were on the tree’s bark when it was sawed, then there might be a connection with the severe reaction you had.

Here is a link to an article (now archived) about splinters from American Family Physician (June 15, 2003).
It does mention wood splinters as a source of severe inflammatory reactions, due to the oils and resins they contain.

A chart which originally appeared in June 1990 issue of the journal American Woodturner lists different types of wood and their toxicity. Elm is included because its dust can be an eye and skin irritant.

growing olive trees in the PNW

I want to grow olives here in the Seattle area. Will they do o.k., and will they produce fruit? I’m especially interested in the variety ‘Arbequina.’

There are some differences of opinion and experience as to whether Olea europaea may be successfully grown here as a fruiting tree. Local tree expert Arthur Lee Jacobson says that “olive trees cannot be expected to ripen fruit in Seattle, but they’re worth planting in warm sunny sites for their ornamental appeal.”

The discussion forum at University of British Columbia Botanical Garden has a question similar to yours, with a reply from Seattle gardener and expert Ron Brightman:
“The olive will grow in a similar spot [against a south-facing sunny wall] but may never produce much of a crop, [and may] freeze out in a hard winter. People grow olive trees in Seattle and Portland, but I have never seen a big one, even here (Seattle area), the mildest of the 3 metropolitan areas (Vancouver-Seattle-Portland).”
Excerpt from a Portland gardener on the same discussion site:
“The Olea europaea that is most popular here (Portland) is the Arbequina, from Spain. It seems quite hardy (we’re colder than you) and I planted one this year and I have two olives on my tree as we speak; they grow slowly and need good drainage and max sun. Jim Gilbert from OneGreenWorld [an Oregon nursery] said that they have had them for several years and they don’t have problems in the winter so far. Mission is another olive around here. They are kind of new. I think people thought only of Greek olives earlier, which would all die.”

Portland, Oregon plant expert Sean Hogan discusses Arbequina and other olive varieties in his book, Trees for All Seasons (Timber Press, 2008). According to Hogan, Arbequina is “hardy to 0 degrees F or even a little below and ripens fairly well in cool summer climates.”

invasive plants and “sterile cultivars”

Is it safe to plant Cytisus scoparius ‘Moonlight’ here on Whidbey Island? I know that Scotch broom is thought to be invasive, but I wonder if maybe this variety is less of a problem.

Some sources (such as the State of Oregon’s noxious weed control board) have said that “sterile cultivars” of Cytisus scoparius are exempt from regulations governing noxious weeds. However, the Center for Urban Horticulture’s Professor Sarah Reichard, an expert on invasive species, says the following:

“The ‘sterile cultivar’ issue is huge worldwide. The reality is that sterile cultivars depend on the type of sterility: there are many reasons a plant might be sterile. Only a few of them can be considered to be stable under varying environmental conditions.

Regardless of what is done in Oregon, in Washington it is illegal to sell or grow any cultivars of Cytisus scoparius. Moonlight is less aggressive, but I have definitely seen it seeding out. But it does not matter how aggressive it is: it is still on the quarantine list in this state because that is the way the state law is worded. Island County may not have it on their high profile noxious weed list because it is only a B non-designate there because it is widespread. But our noxious weed (control) and our quarantine lists are two different things in this state and it is quarantined here.”

For future reference, here are links to Washington State Plant Quarantine and Noxious Weed lists.

pruning winter-damaged plants

How should I prune winter-damaged Phormium, Hebe, and Spanish lavender? The Phormium leaves look wilted. They are folded over and discolored but not blackened. The Hebe ‘Autumn Glory’ and ‘Great Orme’ are blackened, while ‘Shamrock Purple’ is mostly brown. The Spanish lavender has some blackened foliage, but mainly just got weighed down with snow.

My advice for right now would be only to prune any branches which were broken under the weight of the snow. We may yet have more cold weather, so you don’t want to make your plants any more vulnerable.

You may want to wait until early spring or at least all danger of further frost or snow and ice to prune your Spanish lavender (Lavandula stoechas). Under normal circumstances, Spanish lavender can be pruned back by a third to one half in early to mid-autumn, according to Lavender: The Grower’s Guide by Virginia McNaughton (Timber Press, 2000). I grow Spanish lavender, and I usually tidy the plants a bit when most of the flowering is done. However, because of the extreme cold to which your plants were exposed, you may want to assess them in spring, and prune out any dead areas, or replace any mostly-dead plants.

I recommend giving the Hebe plants a chance to recover. I have heard of very sad looking Hebes coming back, perhaps not the first summer, but by the following year. By mid- to late-spring, you should be able to tell what is truly dead and prune it, though Hebes sometimes dislike hard pruning. The Hebe Society of New Zealand suggests pruning frost-damaged shoots in spring.

An article in the Kitsap Sun from May 2011 by Kitsap County Extension agent Peg Tillery mentions hard-pruning winter-damaged Hebes which manage to recover.

You may find this information from Oregon State University useful, as it evaluates the cold hardiness of individual species of Hebe. Here is an excerpt:
“Major cold damage will cause browning of most of the leaves on the canopy, followed by dieback. Sometimes, plants will recover over a 2-3 year period from this damage if subsequent winters are mild. Very severe, sudden cold often turns the entire plant brown and sensitive cultivars do not recover from this damage and require replacement.”

There is a discussion of winter-damaged Phormium in Houzz, an online gardening forum. Again, I suggest waiting until spring to see if only parts of the plant are dead. Keep in mind that gloves are essential when pruning this plant!

The Oregonian has an article about the effects of the December 2008 cold and snow on tender plants. Here is an excerpt:
“I hope, unlike me, you’ve had better luck with your phormiums surviving the storms. Not to be negative, but chances are you didn’t. On the positive side, though, they’ll most likely only die to the ground. If you cut them back, phormiums often come back from the roots.”

controlling Clematis vitalba

I would like to know about controlling Clematis vitalba which is invading my garden from next door.

Clematis vitalba, also known as Traveler’s Joy or Old Man’s Beard, may be a challenge to control without some cooperation from your neighbor. If your neighbor will agree to keep it from going to seed, that will help a little. You might also persuade the neighbor to eradicate the plant, which is a Class C Noxious Weed in Washington State (and in King County), meaning that it is widespread, and enforcement of control is optional but recommended. It is listed in the GardenWise booklet (copies available in the Miller Library and in some local nurseries) which describes noxious weeds and alternative plantings.

The Northwest-based website of Rainyside Gardeners has useful directions on getting rid of this vine. Here is an excerpt:
“The first step in the removal of traveler’s joy requires cutting the plant’s stems above the ground. It is important to make sure the space between the two pieces is large enough to prevent the stem from reattaching itself to the root. Stems can reroot if left in contact with the ground for a long period of time, so periodically move any portions of the plant left in situ. Do not tug on the stems still in the trees. Gravity never sleeps! Pulling on the stem might bring down more than you can handle (all the stem, host branches, or possibly the entire tree).

Digging out the roots of the traveler’s joy is surprisingly easy, but these roots may extend for a long way. Often the roots will be a tangle of overlapping coils and may even come from a distant plant. After that task has been accomplished, a gardener will need to be on the look out for the seedlings that may pop up.

Traveler’s joy is an insidious pest because it readily reproduces vegetatively and by wind cast seeds. The vine-like growth habit spreads myriad possibilities of reproduction over a large area. If a neighbor has an untended C. vitalba, a gardener may find themselves cleaning up their neighbor’s mess.

Because the roots run shallow, simple ‘pull and pile’ is the best method to kill C. vitalba. Some sources suggest bagging all removed sections of the plant, for an off-site disposal, or burning on-site. Burning adds to the air pollution and may attract unwanted attention from authorities who carry weapons. Therefore, burning should be avoided. Simply moving the pile periodically, or placing the debris on an impervious surface until it has died and begins to decompose, may be all that is needed.”

color change in Cotinus coggygria

I planted some beautiful Cotinus coggygria ‘Grace’ in practically full southern exposure in my yard, and their foliage has gradually turned from deep wine red to a pale olive green. Is my soil not acidic enough? Did I overwater? Or is it something else?

You are not alone in noticing this color change. I found the following discussion about Cotinus coggygria x Cotinus obovatus ‘Grace’ on a Houzz forum. Here is an excerpt:
“The true ‘Royal Purple’ smoke bush will not turn green. Some smoke bushes are grafted, most do not grow true from seed. You must order one from a true nursery or visit a specialty nursery to get a good Royal purple smoke bush. There are also many different purple smoke bushes who have different characteristics. ‘Grace’ is a hybrid cross between the green smoke bush and Velvet cloak (which is a gorgeous true purple smoke bush). ‘Grace’ has blue green leaves with red tinges around the leaves.”

An article by David Wheeler in the British paper The Telegraph describes this variety of Cotinus:
“A hardy plant of exceptional beauty at several different times of the year, Cotinus ‘Grace’ has nothing of the leaden darkness so often criticised by those who dislike purple foliage. Less purple than red suffused with green, the leaves bring a bold note to the garden that can complement or offset other foliage colours.

‘Grace’ is a garden hybrid, one of five seedlings resulting from a deliberate cross between the American chittamwood (Cotinus obovatus) and a variety of the Venetian sumac (C. coggygria ‘Velvet Cloak’). Raised by Peter Dummer, propagator at Hillier’s nursery, in Winchester, in the late 1970s and named after his wife, it has won the Royal Horticultural Society’s top awards. Like both parent plants, it exhibits long-lasting autumn colour, the prominently veined, broad oval leaves (up to 5in long) turning to a brilliant scarlet before falling in mid-October.”

A page from Woodlanders Nursery catalog suggests the green phase is normal:
“Reddish new foliage turns blue-green and finally good orange, red, and yellow in fall. Plant in a sunny location with well-drained soil.”

The Brenton Arboretum in Dallas Center, Iowa describes the leaf color change similarly:
‘Grace’ – Hybrid between C. coggygria and C. obovatus; large pink panicles; leaves 4 to 6″ long, light red when young, turning blue-green in summer and red, orange or yellow in autumn; height estimated 20′; zone 5.

It sounds to me as if the leaves go through several changes, and your patience will probably be rewarded with the expected fall color in time.

proliferations and daylilies

I have a daylily that starts new plants from a flower stem. I have not seen this from any of my other 15 or so plants. Could you tell me what might be going on?

When you say “starts new plants from a flower stem,” do you mean a new baby plant develops atop the flower stem (similar to a multiplier onion)? If so, this could be caused by the seeds sprouting in the pod, which does sometimes happen with daylilies. There is also a phenomenon Diana Grenfell (author of The Gardener’s Guide to Growing Daylilies, Timber Press, 1998) terms ‘proliferations:’ “Proliferations are small fans of leaves occurring on the scapes,” [i.e., the flowering stalks] “usually where there is a node or bract just below the point where the scape branches. On some daylilies these proliferations can develop into baby plants…In theory, if the rooting part of the proliferation can be brought into contact with soil or a growing medium, the proliferation will develop into a fully fledged daylily genetically identical to the parent plant.”

controlling rose sawflies

I think my rose leaves are being devoured by rose sawfly, and I was wondering if spraying ‘Rose Defense’ on them would help.

Rose Defense is a Scott’s product that contains Neem (as well as other ingredients). There is some evidence that Neem is effective against sawfly larvae. As with any pesticide, you should follow the directions on the package carefully (and note that this product may be harmful to humans, domestic animals, bees, and the environment, depending on the route of exposure).

You might want to start out with the least toxic approach first, that is, handpicking and spraying with water. Once larvae are knocked off the roses, they will not climb up again. If this doesn’t seem to be helping, then you could choose a Neem-based spray or insecticidal soap, keeping in mind that the Neem product is toxic to bees, and should not be applied when bees are active.

According to University of Minnesota Extension, sawflies are best controlled when young. You can simply pick them off by hand or dislodge them with a stick or a stream of water. If using water be sure to spray early enough in the day for the foliage to dry by sunset. This will prevent favorable conditions for fungal development. Horticultural oil, insecticidal soap and azadirachtin (sometimes called neem), are among the less toxic insecticides to treat young sawflies. Azadirachtin is slower acting. Bacillus thuringiensis (Bt) is effective on young lepidoptera caterpillars but NOT on larval sawflies.

Cornell University’s Resource Guide for Organic Insect and Disease Management also discusses the uses of Neem. Here is an excerpt:
“Neem products are generally sold as emulsifiable concentrates. Neem oil soap is sold as a water-soluble liquid concentrate. While Copping (2001) reports no known incompatibilities with other crop protection agents, phytotoxicity may be a problem when combining neem oil or soap products. Read labels for specific application guidelines including determination of re-entry interval and pre-harvest interval. Range of efficacy will depend on the susceptibility of species in question and environmental conditions at time of application. However these are points to follow:

Make multiple applications. Frequent applications are more effective than single sprays because neem does not persist well on plant surfaces. Like most other botanically derived materials, it can be rapidly broken down by sunlight and washed away by rain (Thacker 2002).
Use against immature insects. Azadirachtin-based insecticides act on immature stages of insects more effectively than on eggs or adults. To reduce a build up of populations it is important to make treatments to crops targeting insects in an early stage of their life cycle. For instance, neem would likely have little effect on an infestation of striped cucumber beetle adults; however if applied to potato plants early in the season, it has been shown to greatly reduce larval activity of Colorado potato beetle.
Begin applications before pest levels are high. Antifeedant and egg-laying repellant effects show best results in low to moderate pest populations.
Neem is reported to work best under warm temperature conditions (Schmutterer 1990).”

There are quite a few different species of sawfly, and I would guess that the rose sawfly is so named because rose bushes are its primary feeding ground. If you aren’t sure what is eating your roses, you may want to take samples of the affected leaves to your local county extension agent before you begin to treat the problem. You may find the images on the self-described Buggiest Rose Website (now archived) helpful in comparing with the leaf damage you are seeing.

propagating and grafting Ginkgo biloba

Onto what root stock should I graft a Ginkgo biloba scion?

According to The Complete Book of Plant Propagation (Taunton Press, 1997, Jim Arbury et al.), Ginkgo biloba can be propagated without grafting, by taking semi-ripe cuttings in midsummer and dusting them with rooting hormone and potting them up in a mixture of half peat, half sand/vermiculite. Cuttings should root by spring if kept moist, and need to be planted out once they have roots.

If you wish to graft it, you need a Ginkgo biloba rootstock, which you could grow from seed if you have access to a female ginkgo tree (they are hard to find), and (according to the American Horticultural Society Plant Propagation manual) you can use a whip-and-tongue or spliced side veneer graft done in late winter. The AHS manual also recommends taking softwood cuttings in late spring or early summer for ginkgo.

There is also helpful information from The Ginkgo Pages and Plants for a Future Database, which says that softwood cuttings are taken in spring, semi-ripe cuttings are taken in July and August, and hardwood cuttings are taken in December, and all are kept in a frame.

growing Hibiscus from cuttings

Can you tell me how to grow Hibiscus from cuttings?

According to the American Horticultural Society, most hibiscus root easily from cuttings. They suggest the following in Plant Propagation (1999, p. 131 and pp. 100-101):

“…cuttings should usually be 1.5 to 2 inches long, with two or three pairs of leaves retained at the top…remove the soft tip from each cutting, because it is vulnerable to both rotting and scorch…remove the lowest pair of leaves to make it easier to insert the cutting into the medium…make a hole in the medium with a pencil…[for]…minimal resistance…the cuttings will benefit from a warm, protected environment…when the cuttings root, knock them out of the container and gently pull them apart. Pot singly…”

The AHS suggests using rooting hormone and they also point out that due to timing, you may get ‘greenwood’ (slightly hardened) rather than ‘softwood’ cuttings; they are treated the same way.

North Dakota State University Extension has propagation directions including from cuttings.

I also looked at Houzz (formerly GardenWeb), a gardening forum where experienced gardeners share their knowledge. Here is another link from this site which suggests layering, a process by which you bend a branch down to soil (usually in a pot), anchor it, and wait for it to take root.

Here is additional information about layering hibiscus, from Hibiscus World.