Thursday, November 23, 2006
Prune rhododendrons after the flowers bloom
John Arbogast
Landscape consultant John Arbogast answers your questions every Thursday. Send questions about your lawn, garden, plants, or insects to:
Dear John
5102 Greenfield St. SW
Roanoke, Va. 24018
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Q: Can rhododendrons be trimmed back without damaging them? And when is the best time of the year to do so?
A: Vigorous rhododendrons can be cut back to about half their size at the time of year when new growth can easily be produced and maintained. The best time to do this is immediately following their flowering in the spring or early summer. This timing allows enjoyment of the rhododendron's flowers before ends of branches are removed. Pruning time also leaves many weeks for new growth to emerge and “mature” so that flower buds for the following spring can be produced on branch ends.
If for some reason the rhododendron pruning must be done in early or mid spring before flowering, vigorous plants will not be harmed. The drawback to that is that the flower buds that have lived through the winter are cut off before they can open and add their beauty to nature.
Weekly watering during the remainder of the growing season through mid fall is suggested for rhododendrons that are cut back by half if the weather is dry. Your summertime goal is to eliminate all adversities that might occur to hurt the rhododendrons
Q: I've been reading a booklet from Jackson and Perkins Rose Company about necessary fall care. We planted 12 rose bushes this past spring. What care for fall do you recommend for roses that bloom for the entire summer here in the Roanoke area, and when in this area should things be done for roses bushes?
A: The grafted portion on each rose plant must be protected for survival through the winter. Luckily, rose breeders have worked to meet demands from both environmentalists and busy gardeners to produce new rose varieties that seem to be stronger.
Roses stay green and in active growth later in the fall than most deciduous landscape shrubs around here. The green leaf color signifies the continued reception of sunlight, which means that the plants are still producing food that is being stored in their canes and roots. As a result, most bush-type roses grow tall during the autumn weeks. We must resist the temptation to do heavy pruning on those long canes.
Instead, the only fall pruning that is advisable during the mild to cool days while the garden roses are sill green and growing is the prompt removal of faded blooms. Then, soon after the bush roses shed their leaves and go dormant, all long rose canes should be lightly cut back so that winter winds don't push and pull the shoots, which could loosen or damage the plant. It might be mid to late December in Roanoke before this cutting is suggested.
At the December cutting time, sanitation of both the rose canes and the beds is suggested. This helps prevent rose disease infections from surviving the winter and then causes problem next summer. For rose sanitation, rake and remove rose leaves, some of which will have black or dark gray spots that are rose black spot disease and the causal organisms that will live on leaves in a inactive state until they can cause new black spots disease spots in the coming summer. Also, sanitation includes pruning and removal of all cane portions that show reddish-purple black spot blemishes and/or tan or chestnut-brown cane spots surrounded by deep purple edges, maybe with cracks, which are symptoms of rose stem canker diseases.
Fall fertilization of bush-type roses is usually not recommended here. Roses culture is like that of annual flowers in this respect that are fertilized in the spring to encourage lush growth and blooming in the weeks ahead.
Another required late fall or early winter rose job is to place winter protection over the graft union soon after the roses have become dormant and the ground has chilled. The purpose of this required protection is to ensure that spring rose growth will be from the grafted parts instead of the rose roots, which might be of a different rose bloom color or different cane stoutness from what you planted.
For this protection, Roanoke-area rose growers don't have to build a tall mound over roses like folks in northern climates do, as might be explained in your booklet from Jackson and Perkins Rose Company. Instead, we can protect the rose graft area by placing a 10-inch tall mound of coarse mulch over the lower portion of dormant rose canes. This should be adequate in Roanoke to insulate the graft union. Then, next spring, the mulch mound should be pulled back from the lower rose parts, rose fertilizer can be sprinkled over the rose roots ground and the pulled-back mulch can be spread around the plants.
