Q My Norfolk Island pine is kept indoors year-round in a sun room. After nearly eight years of ownership the plant is now at least eight feet tall and still growing. I have never repotted or fertilized it. Is it possible to curtail future growth by pinching back the new shoots at the top of the plant, or is it destined to outgrow my sun room?
A As a rule, conifers will not grow new central leaders if you cut back the trunk to reduce the plant's height. If you lop the top off, the existing side branches will continue to grow sideways, and you will end up with a strange, palm-like plant, especially since the lower branches tend to die with age.
The Norfolk Island pine really is a temporary houseplant. Keep it for a few years, and then get another one if you really like the plant. In subtropical and tropical areas, it may reach more than 100 feet. It may be moved outdoors in frost-free climates, but indoor gardeners here are unable to accommodate it for more than five to 10 years.
I am hoping you can help my tomato growing finally succeed in 2005. Unable to rotate my tomato bed due to limited sunlight, I devised a way of giving the vines fresh, disease-free soil by sinking large plastic pots, filling them with compost and growing the plants in those.
In the past two years, the plants became infested with spider mites and bore little fruit. I dislike using insecticides and by the time I resorted to them the damage was done -- the blossoms had dropped off and the plants were nearly dead.
Are there any varieties resistant to this pest? Should I just give up tomatoes if I can't rotate them?
Spider mites are not a major problem with tomatoes in our area. Heavy rains wash them off the foliage. You may want to use a jet of water from the garden hose on a weekly schedule to keep them off the plants, particularly during hot, dry periods. Do this in the morning so the water quickly evaporates and doesn't promote fungal diseases.
Crop rotation is not a terribly important consideration for spider mites. In clean garden beds they cannot survive the winter. Mites arrive in the spring on the wind or may be present on the plants you bring home from the nursery.
Sometimes those plants that you purchase have a few mites whose population explodes when you set the tomatoes out in the garden.
The key is to monitor plants carefully. Inspect them weekly after they are planted. Look for stippled leaves, and shake a few leaves over a white sheet of paper to detect any mites that might be present. If you find mites, you can blast them off with water, or you can treat plants with a 1-percent solution of horticultural oil. Oil is a non-toxic alternative to miticides and has the advantage of killing eggs as well as nymphs and adults. Be sure to spray the plants only when the solution will dry rapidly and keep the spray solution well agitated during the application. Oil is a contact pesticide, so spray the plants very thoroughly.
Scott Aker is a horticulturist at the U.S. National Arboretum.
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