Thursday, September 25, 2008
Q My bed of Saint-John's-wort, variety Albury Purple, is experiencing some kind of dieback. The leaves turn dark purple, wilt and then turn brown. I've lost several bushes; will I lose the whole bed? Is it safe to put other plants in there? The area is mostly full sun, and it is mulched with shredded bark to keep down the weeds.
A Several fungi may cause the wilt symptoms that you describe in Saint-John's-wort. Cut the plants back entirely to rejuvenate them and stimulate new growth. The cultivar you describe, Albury Purple, is often cut back each spring since only new growth has the dark-purple leaf color. The leaves eventually age to green. Cut it back now that the weather has turned hot and a bit drier, and conditions are not favorable to the fungi that cause the disease.
The severity of the disease this year is most likely related to the wet weather we have had. It may not appear again in drier years.
I have six amaryllis plants that I keep from year to year , but only one produced a bloom this year. I leave the plants outside in the summer on the back deck , where there is bright, indirect sunlight. They thrive.
In the fall, I put them in paper bags in the basement. The following March, I snap off the old, dried foliage and start the bulbs by potting and watering them, and placing them on a south - facing windowsill. How can I get all six to bloom next spring?
First, find an even sunnier place for them in the summer. Full sun, regular feedings with a liquid fertilizer and soil that is kept constantly moist will translate into nice big bulbs that are primed to bloom. Amaryllis usually grow four leaves and a flower bud in sequence, so if you want one of those plants that produces three or four flowering scapes, you need to grow at least 12 leaves on your bulbs throughout the growing season.
The embryonic flower buds inside the bulbs will not develop any further if their chilling requirement is not met, however. Amaryllis are native to areas that have a cool, dry season and a warmer, rainy season. The bulbs must experience about 10 weeks of temperatures below 65 degrees to bloom well. It is best for the bulbs to be dry during this cool period.
In our climate, it is easiest to emulate these seasonal conditions by growing your amaryllis outdoors throughout the summer and early fall. When cooler weather arrives at the end of this month, place the plants in an area where they will be sheltered from most rains, such as under an eave.
Don't be in a hurry to bring the plants indoors, even as they lose their leaves with this dry treatment. Keep them out until a heavy frost is forecast. This may be as late as mid-November. When you bring the plants in, keep them in a cool location such as an unheated basement until after the holidays.
If you then move them into a warmer location for about four weeks before starting the bulbs, you will stimulate new leaf growth at the same time as emergence of the flower scapes. Otherwise, you might find the flower stalks poking out of the bulbs in February or March with the leaves slow to play catch-up, and the plant won't look as handsome.
Scott Aker is a horticulturist at the U.S. National Arboretum.