We’ve passed the winter solstice and that means we’re on the way to spring and the gardening season. If you’ve got questions, turn to Ask an Expert, an online question-and-answer tool from Oregon State University’s Extension Service. OSU Extension faculty and Master Gardeners reply to queries within two business days, usually less. To ask a question, simply go to the OSU Extension website and type in a question and the county where you live. Here are some questions asked by other gardeners. What’s yours?
Q: I have Anna’s hummingbirds year round who nested in my yard last spring. A neighbor posted that these birds mate starting in December. My question is how soon do they nest after mating? I usually have all my trees and shrubs cut way back in the late winter (February and early March) and don’t want to disturb any nests. – Marion County
A: This is a great question, and worth considering as you decide when to do your winter pruning.
I found this on the Audubon Society’s website regarding Anna’s hummingbird nesting: “May begin nesting in December, or even earlier. In courtship display, male hovers in midair, giving buzzy song, then flies much higher; he then dives steeply toward the female, making a loud explosive popping sound at the bottom of the dive. Also buzzes back and forth in front of female in short shuttling flights. Nest site is variable, usually on a branch of tree or shrub, sometimes in vines, on wires, under eaves. Usually 4-25 feet above ground, can be lower or higher. Nest (built by female) is a compact cup of plant fibers and spider webs, lined with plant down and sometimes feathers, the outside camouflaged with lichens.”
It is likely that you have nesting pairs right now, so care in choosing branches to prune is a good idea. You may wish to observe for a period of time where the birds are flying regularly to get an idea of possible nest locations. If you happen to see trees visited frequently that you plan to prune, inspect those branches for evidence of nest building. As mentioned in the description above, the nests are often camouflaged, and quite high off the ground, so it may be a challenge to find nests. Some taller branches are used as territorial perches, so even if you see the birds use a tree, it doesn’t mean it is the nesting tree. Leaving some taller branches for such behavior may be worth considering as you plan your pruning. If you are concerned that you might disturb nesting, you may consider pruning later in the winter, closer to the tail end of pruning season in March.
This OSU Extension article on tree pruning is a useful guide. It recommends pruning between November and March. – Jason O’Brien, OSU Extension Master Naturalist statewide coordinator
Whiteflies are unlikely to be active in the garden during winter. Image by USDA Agricultural Research Service
Q: Would an application of neem oil during winter (December through March as a dormant oil) on days above freezing temperatures be appropriate? White flies have infested my garden especially in hellebore and western sword fern beds. Applications of castile liquid soap sprays in the evening and cutting back all ferns to the ground last February didn’t slow down the infestation. I had hoped the soaps would clean off active insects.
What can be done before next spring’s growth of plants and insect population, and during the growth season? The property is in an active watershed full of native birds, wild bee populations, and other beneficial insects, and native frogs, and which need protection from anything toxic. – Washington County
A: Neem oil is a fungicide, an insecticide and a miticide. However, like other topicals (as opposed to systemic pesticides), it is effective only when applied at the right stage of the pest’s life. Here is a fact sheet on it. I doubt that your insect population is active now, so any insecticide application will be useless. Here is an excellent Extension article on this pest, with a variety of control recommendations. – Kris LaMar, OSU Extension Master Gardener
Q: We wish to plant 200-plus evergreen trees zig-zag along our community park border. We want to plant 4-year-old seedlings on the berm, which is 6 to 7 inches of good topsoil and clay subsoil. What conifers do you recommend? Can you we novices to planting instructions? – no county given
A: Your choice of conifer depends on your geography and climate as well as the soil condition. It also depends on the topographic position. Clay soils in low or flat areas often stay too wet to support healthy roots for many species. But some clay soils on hillslopes or other well drained topography can be quite productive for conifers.
Here is a reference with some ratings of tolerance and other guidelines for establishing native trees.
Willamette Valley ponderosa pine often tolerates and roots into both clayey and rocky subsoil. Most other native conifers are not happy on wet clay. Western redcedar may tolerate a wet clay subsoil, but it is vulnerable in drought years with shallow rooting depth on clay.
In northwest Oregon, Douglas-fir especially does not do well on heavy clay that is poorly drained.
When it comes to exotic ornamental species, you may have more choices of conifers, but that is not my area of expertise. – Glenn Ahrens, OSU Extension forestry specialist
Q: The three clumped, very tall spruce trees in my Lincoln City yard have huge exposed roots. I want to make some changes in my yard that might include leveling the surface somewhat. It would (or would not) involve putting soil over 50% (south side of trees) of the exposed roots, which run across the width of the yard. Is this a good or bad idea? If I do place some topsoil on the roots, is there a limit to the amount? I would leave 50% of the roots (north sides) as is, uncovered. – Lincoln County
A: It is not recommended that soil depth be changed, either more or less, for established trees. Tree roots actually absorb air through exposed roots, and covering them with soil as little as 4 to 6 inches deep dramatically reduces air and water (which has dissolved nutrients in it). Here is an Extension article on tree care with advice on this. Perhaps you can consider potted plants, staggered over the area. – Kris LaMar, OSU Extension Master Gardener
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Careful winter pruning may help avoid disturbing early nesting hummingbirds: Ask an expert - OregonLive
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