Summer is a season for deadheading, also known as removing spent flowers. We prune roses back to outward-facing buds, and remove other flowers that are past their glory by pruning or shaking the plant hard enough that the spent blossoms fall off. If we didn’t do that, most of the perennial plants would not bloom again until next year, and the annuals would just set seeds and die. It is about time, though, to quit deadheading roses so they can prepare for winter. Many rose shrubs will set hips or seed packets as they get set for wintry winds. We used to recommend no more rose deadheading after Aug. 1, but many wait until September dawns before ceasing that task.
We can spark continuous blooming in most plants by removing those withering blossoms before they are replaced by seed heads. Exceptions are lilies and irises, unless you have the less common reblooming iris. Some plants such as rhododendrons have next year’s buds immediately behind this year’s flowers, so taking care in plucking off those spent flowers guarantees their blooming next year.
Pruning also may be done to improve airflow within a shrub or plant, and usually results in rejuvenating the plant, so it’s very beneficial treatment for ornamental gardens. In spring and early summer, we prune asters, forcing them to bush out, so that when they set flowering buds, they’ll set very many more than before they grew lusher. Shear back early aster blossoms for more and more, well into autumn. Do not prune back to brown on needled evergreens, though.
I’ve heard some folks set lawn mowers to cut high and mow over petunias to encourage reblooming. That can severely damage leaves that are feeding the plant, so I think that’s risky. Speaking of petunias, though, now is a good time to take stem cuttings of petunias, dip cut ends into root hormone powder and flick off excess, and insert dusted cuttings into holes in potted plant mix. Three or four of your most fragrant petunias in a pot may be grown indoors over winter, perfuming the air and brightening spirits. Digging a mature plant and potting it will result in an untidy, overgrown plant in a pot, so take cuttings now.
New gardeners are often hesitant to prune plants, and tend to panic if one leaf among many is discolored or visibly damaged by insects. If you’re one of these, relax. If a part of a plant is deformed or discolored, remove it if you wish, pruning an ugly plant into a more desirable shape. If a plant has a disease that’s communicable to other plants of its type, you may prefer to remove it. Do not compost diseased parts, but bag them securely and put them in the landfill-bound trash. Some folks remove plants afflicted with curly top virus, but I haven’t for these reasons: The virus was transmitted by a beet leaf hopper who rides the winds, and is probably in another county or state by the time the plant shows signs of virus; and the virus doesn’t affect the fruit as far as human consumption is concerned. The few times that virus has appeared in my garden, tomatoes were nearly ripe.
The transient nature of beet leafhoppers also means that you really can’t spray anything to control them, but you can prevent their destruction by providing afternoon shade or surrounding plants with strong-smelling herbs such as dill or planting resistant varieties. Yellow sticky traps may catch some, but they also catch gardeners and sometimes beneficial insects. Resistant varieties of tomatoes include RowPac, Saladmaster, Latah, Owyhee, Payette and Roza, all salad-size tomatoes. Seeds for those varieties are sold only by Sandhill Preservation as far as I know, and those folks do not claim curly top resistance. When introduced to the public, those varieties were said to be resistant.
We may not be finished with hot weather. September has been one of the hottest months in some years. Some plants, such as Clematis, prefer cool roots, and hot weather produces hot soil if it’s left bare. A good layer of mulch insulates the soil from high heat, protecting the roots. In some cases roots are more vulnerable to heat or cold than the above-ground part of the plant.
Send garden questions to email@example.com or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.