Q What evergreen trees would grow in a woods with a lot of shade? I would like to plant cedars or some other conifer in an area shaded by maples and oaks, although there's a little sun in spots.
A A few evergreens will grow in some shade, but not if the shade is very dense. You may have better luck if you plant the evergreens close to some of the sunny openings so that they can get a better start on competing with the existing oaks and maples.
One beautiful evergreen that grows well in shade is Canadian hemlock (Tsuga canadensis). Native from Nova Scotia to parts of Minnesota, Canadian hemlock prefers moist, cool, slightly acidic soils. Canadian hemlock grows about 30 to 60 feet tall. It has a pyramidal form, with graceful, gently drooping branches. The short needles are dark green and give the tree a soft, feathery appearance.
Hemlock does not tolerate drought, so you may need to provide supplemental water, especially when the plants are young. It can also suffer from winter burn in windy, exposed sites, so tuck it into protected areas when possible.
Arborvitae, or white cedar (Thuja occidentalis), develops its best shape when grown in full sun, but it will grow in some shade also. Arborvitae will not be as full and dense when grown in shade.
Used extensively in landscaping, arborvitae is valued for its hardiness and attractive foliage. Unfortunately, deer also find its foliage quite attractive and browsing damage is a common occurrence. Arborvitae will grow in a wide range of soil types, but grows best in moist, well-drained and fertile soils.
Another native evergreen tree that will grow in some shade is balsam fir. Common in northern Minnesota, balsam fir needs cool, moist soil to grow well. It grows tall and narrow with a spire-like form. It has short, dark green, wonderfully fragrant needles.
Q Some of my lilac bushes get a white fungus growing on the leaves. Should I spray them with something? Also, one of them is not growing well. Could the fungus have moved to the roots?
A The white fungus growing on the lilac leaves is powdery mildew. Many lilacs, especially the commonly grown French hybrid lilacs, are very susceptible to this. Powdery mildew usually develops in late summer on lilacs. While the mildew looks unattractive, it won't damage the lilacs, and it's not necessary to treat it.
The best preventive measure is to plant lilacs in full sun where they have adequate space for good air circulation around the plants. This helps keep the leaves drier, which inhibits the spread of the powdery mildew fungus.
This fungus affects only the leaves, not the roots, of the lilacs. Factors that could be negatively affecting your lilac's growth include overly wet soil or poor drainage, mechanical damage to the trunk (from a weed whip or lawn mower) or damage to the root system. Lilac borer, an insect pest, may be the problem; look for holes at the base of the stems for evidence of borers.
Q I had sunflowers growing in the back yard. Then I found that the leaves were dying, the stalk cracked and fell over. I discovered medium-sized black ants devouring the stalk and leaves. How might this be prevented?
A It's unlikely that the ants caused the problems with the sunflowers. The presence of ants on plants often indicates the presence of those ubiquitous plant pests, aphids. The ants gather a sticky substance known as honeydew from the aphids, and the ants may even drive off other predatory insects in order to protect their aphid "herds." The ants on your sunflowers may have been chasing aphids or other insects, but I don't think they would have been eating the sunflower plant.
The dying foliage and stem cracking on your sunflowers might be caused by a number of things. Sunflowers often seem to have a rather tatty appearance by late summer, so perhaps part of the problem was natural aging.
Sunflowers with especially large seed heads may bend over and cause the stem to crack. Various leaf diseases might make the foliage die back, or perhaps a fungal infection also affected the stems. While I don't know if sunflowers are a particular target, there are many different stem-boring insects that drill holes in stems and chew up the insides, which often causes the stems to break. I've had stem borers on peppers, tomatoes, hollyhocks and salvias.
If you grow sunflowers next year, try sowing some seeds at weekly intervals for about a month in the spring. Then you'll have a succession of sunflowers maturing through late summer. Plant sunflowers in full sun, and keep them spaced far enough apart for good air circulation around the plants. This may help prevent leaf disease problems.
--Nancy Rose is a research horticulturist at the Minnesota Landscape Arboretum. She spends her spare time gardening, inside or outside, depending on the weather. Please address gardening questions to her at the Minnesota Landscape Arboretum, PO Box 39, Chanhassen MN 55317. She will answer questions in this column only.
