This fall has not slowed the flow of gardening concerns. I enjoy learning about your landscapes and answering your questions.
QA four-year-old, healthy looking, white rhododendron has about two dozen buds that appear brown. Why are some blooming now? It usually blooms in late spring or early summer. -- Rusty Flint
APlants grow and bloom on the basis of day length (photo-period) and/or temperature. We have had some sunny days and higher than usual temperatures. The buds are set by autumn, and, if their blossoming needs are met, the flowers will open. This is the theory used in greenhouses to force flowers on plants for landscape displays at home and garden shows.
The weather will change soon and plants will readjust their systems to the season. Most plants that open prematurely retain plenty of buds to flower in spring. If all your flowers opened this fall, the plant might not bloom next spring, but it will the next year. The browning you describe might be flower buds that froze and never bloomed last spring.
I need to rejuvenate an old andromeda bush. It looks bad, mostly old wood up to two feet, with healthy growth at the top. When can I try rejuvenation pruning? -- Margaret Ahmann
If the andromeda bush is Japanese pieris (Pieris japonica), it is a shade-tolerant evergreen that's already showing the beginning of flower buds for next season. The plant, related to the azalea and rhododendron, usually responds well to hard renewal pruning. Pieris blooms early, so you could cut it immediately after the top growth flowers in the beginning of March and avoid sacrificing its blossoms. Take it back to bare wood if necessary. New growth takes a couple months to appear. It comes from the base of the shrub and buds that form under the bark. Given a growing season or two, you should be able to turn it back into a full, lower growing shrub.
We put Reiger begonias on our balcony in May. They bloomed their hearts out and now have several final small flowers. How can they be kept to survive until next year? -- Carolyn Groce
It is not recommended that you try to hold over Reiger begonias because of their tendency for disease and insect problems, including mildew, mold, sooty mold, root and stem rot, mealybugs and mites. Unfortunately, this shade-tolerant, fibrous rooted type of begonia is hard to maintain after it flowers in the summer. Discard these plants when flowering has stopped, and get fresh plants if you wish to try some indoors. Good additional information on this hybrid of elatior begonias (B. x hiemalis) that flower all summer long can be found at www.gertens.com/articles/begonia.html and www.begonias.org.
I have some aucuba bushes that are at least 40 years old. Each Christmas I cut back bunches and give to friends for home decoration. Now, I would like to prune them in a more drastic manner. Is there a good time? -- Leon Schertler
The aucuba, an excellent shade-tolerant evergreen, can grow to six to seven feet. Be exceptionally generous with greens for your friends this Christmas. Wait to make any further drastic cuts until early spring, when you know what winter brings. A bitter cold winter can kill top growth. Waiting until spring allows you to see if there was winterkill that also needs to be pruned. In spring, before growth begins, cut the bushes to any size you wish. Selectively prune the old largest wood to the ground or cut stems in half to a lower stem.
Our lawn has many patches of clover. Do we attempt to rid the lawn of the clover, or feed and lime the lawn first? -- Diane Boyd
Clover is better controlled in late spring as it begins growing and before flowering. As a chemical alternative, you can use herbicides to kill clover, such as Weed-B-Gon or any herbicide that contains Banvel or dicamba. Apply materials on a day that is not windy, following all labeled instructions.
Fertilize, aerate and overseed the lawn in September. Many lawn buffs tolerate clover in their lawns because it is tough to control, stays low, thick and deep green during the growing season and mows evenly. This is a desirable complement to turf grass as a low-maintenance, low-growing plant.
Our house is close to the sidewalk and street, with a strip of lawn six to seven feet wide. About six years ago, we planted two small river birches there. They are now taller than the house (30 feet) and show no sign of slowing. How big will they get? We are concerned that their root systems may damage our foundation. Do you have any guidance that might help us decide whether we have to cut them down to save the house? -- Karin Firsow
The trees will have no effect on the foundation of your house as long as your basement stays dry. If you have a wet basement problem or cracks in the walls that allow moisture to seep in, the roots of any trees will grow toward moisture. With a dry foundation you will be fine.
Your trees have had quite a growth spurt in six years. Yours might grow to 60 feet or more and 20 to 30 feet wide -- in 30 years. Enjoy their canopies and ornamental characteristics. It is a good "small" street tree. Keep the lower limbs elevated over the street, sidewalk, yard and house for comfortable vehicular, pedestrian and air circulation. You will need a pole pruner to keep the limbs above ground level. Cut the lower limbs off at the trunk of the tree, leaving only the widened branch collar at the base of the branch. Never prune birches in spring when they are pushing their new leaves; they tend to bleed sap if you prune them when it first starts flowing.
Earlier this year, you answered a question in this column about the black leaf spots that affect black-eyed Susans. You recommended applying a material in the fall to eliminate this the following year. What is it, and where can it be purchased? -- John P. McCrea
I recommended spreading lime-sulfur. It is available at garden centers and on the Internet, and is intended for dormant use. A common form on the market for homeowners is Ortho Dormant Disease Control Lime-Sulfur Spray. Use it late in the fall (like right now), after cleaning up leaf litter. Apply again in late winter or early spring just before growth begins.
While lime-sulfur is the most environmentally friendly material you can use, there are post-emergent fungicides that can be applied just as plants leaf out in spring. One is a fungicide containing benomyl or captan, but I'm suggesting treatment for a fungal problem without knowing an exact diagnosis. By law the pesticide you use must be labeled for the plant and problem you are using it for. To be sure, call the manufacturer and ask if you will be using one of these post-emergent products correctly. Also, none of these products will replace the right plant for the right place. Black-eyed Susans need full sun and good air circulation and drainage to thrive.
Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. E-mail or contact him through his Web site, www.gardenlerner.com.