By Scott Aker
Special to The Washington Post
Thursday, June 18, 2009
Q How can I save an old Southern magnolia that is in the way of an upcoming remodeling project? Can it be moved or, failing that, propagated?
A I don't recommend trying to move it. It would cost a great deal and may still end up killing the tree, even if it was dug with a very large root ball.
Magnolias can be rooted from cuttings. The cuttings are taken rather late, when the terminal bud has set, sometime between July and early September. Take several cuttings in case some fail to root.
From the base of each cutting, make a two-inch vertical slice with a sharp blade. This wound will encourage root development. Wet the base, dip it in rooting hormone and place the cutting in a pot filled with moistened perlite. Use a pencil to make a planting hole to avoid rubbing off the hormone when you stick the cutting in the perlite.
Put the pot of cuttings where they will get some indirect light. A large, clear plastic bag can be used as a tent to raise humidity and stop them from drying out. Mist the cuttings frequently and keep the perlite moist at all times, and you may see roots in six weeks. After the cuttings are rooted, pot them and grow them through at least one season outdoors before planting them.
I have several photinia bushes, the largest about 20 feet high. Ten years ago, I trimmed back a couple of them and the resulting fresh growth was afflicted with the leaf spot disease, which ultimately killed them. Last summer I had to trim one big bush back a bit, and now the spot is back. I'm doing what I can, avoiding more pruning, raking and disposing of fallen leaves and spraying with a fungicide. Is there anything else that would be helpful?
Your photinias are suffering from a fungal disease named Entomosporium. It is common on photinia and several other plants in the rose family. It may defoliate plants and kill succulent new growth if it becomes severe.
You can manage this disease by avoiding the use of fertilizer or watering your photinia. This will prevent the kind of rank growth that is most commonly damaged by the disease. You should use a light hand with pruning for the same reason.
Fungicides prevent new infections but are effective only if applied frequently, beginning when new growth starts in spring. You must spray your photinia throughout the growing season because new infections can take place over such a long period. With much rain this spring, untreated photinias are bound to be affected. Given this chronic condition, you may want to replace your photinias with some other evergreen screen, such as Burford or Foster's hollies or the Southern wax myrtle, Myrica cerifera.
Scott Aker is a horticulturist at the U.S. National Arboretum.