August gardening and roses

This red "Francois Rabelais" grown in a container was selected by Julieta Moran for her Malibu garden because it originated in the south of France. She had enjoyed success with another rose hybridized in southern France, "Michelle Meilland." The foliage and flower are healthy and disease resistant. Peggy Harris / TMT

Malibu Garden Column/ By Peggy Harris

Often it is the roses that invite the concerned Malibu gardener out to check the health of the plants and to prune in the summer sun. Roses are productive, needy and rewarding enough to merit daily attention. The summer months should be filled with cutting, trimming and deadheading as well as harvesting vegetables, fruit and flowers.

Focusing on roses, I want to take a closer look at a feeding and care plan designed to combat some of the most common coastal rose problems, which usually include powdery mildew, rust, black spot and aphids. Once you learn to control these problems on roses, the same knowledge carries over to the problems on fruit trees and most areas of the garden, although it is always wise to consult books, read labels and talk to local nurserymen about species-specific problems.

The problem of powdery mildew on roses may be somewhat abated when the August and September heat takes over. Powdery mildew is a fungus and the type found on roses is species specific solely to the rose. To combat this mildew, spray the roses with soap and water or prune and discard all rose parts with mildew.

Black spot, diplocarpon rosae, and rust are caused by fungal spores, which are spread by splashing water. Leaves exhibiting black spot or rust should be cut and removed. Whenever possible, keep the fungus-bearing materials from sitting on the ground under the rose. The fungi will survive in the soil. Rusts infect many plants: birches, fuchsia, hawthorn, juniper, pine, poplar and roses. Raking up leaves and using deep soak watering are among the best for controlling rust before resorting to fungicidal sprays.

Treatment for black spot, rust and powdery mildew is to begin with correct practices of watering and cutting out diseased plant material. When this approach isn’t working, try these products: Rose Defense, Green Light Fung-Away and Safer. These products contain neem oil (from the nut of a tree) or sulfur (a naturally occurring element). Sulfur works as a broad-spectrum control for fungi and mites. It binds with fungal spores to prevent their germination. Sulfur is not toxic to aquatic life, birds and bees. It is safe for use on roses, vegetables, flowers, ornamentals and fruit trees.

Aphids will appear on healthy new rose growth, sucking the juices from the new rose blooms. During summer, aphids will reproduce every two weeks. A soap and water spray and frequent washing can keep the aphid population under control. Biological controls for aphids include lady beetles, lacewings and small wasps that lay eggs inside the aphids, killing the host.

For pest control with roses and all trees and shrubs “the best defense is always a good offense.” A healthy rose will be able to tolerate a small number of aphids and some black spot or rust. The roses at Lotusland are sprayed with a “compost tea” made from soaking compost in a barrel of water.

One approach Rayford Clayton Reddell, writer and rose specialist, offers in the concise book “A Year in the Life of a Rose” includes a vigorous feeding schedule. Reddell spells out his formula from March to April; he feeds a formula high in nitrogen for growth. He uses granular fertilizers and applies around the drip line of the rose. After three weeks, he adds three-quarter cup of Epsom salts (magnesium sulfate) around the base of each rose to activate plant enzymes for growth. In May and June, he feeds granular fertilizers with an even distribution of nitrogen, phosphorus, and potassium (NPK). Reddell uses a fertilizer with NPK of either 10-10-10 or 20-20-20 (whichever is cheaper, he states) in the first week of May and June, sprinkled around the drip line. He follows this in the third week of May and June with three-quarters of a cup of Epsom salts per plant. In July and August he gives the roses a similar 10-10-10 or 20-20-20 feeding and three weeks later a fish emulsion solution with water. In September and October, his feeding cuts back to a 0-10-10 fertilizer on all his garden plants to stop encouraging new growth. At this time he is encouraging continued blooming and hardening plants for winter. Three weeks later he applies fish emulsion again. Reddell does not fertilize plants after Halloween. If the gardener adheres to this heavy feeding schedule, he can expect better results from roses. Although the rose feeding schedule seems intensive, the principle makes sense for all plants; the healthier they are the more they are able to withstand fungal diseases.

In August, with every cutting of one’s roses the gardener is pruning for the next growth. Some experts advocate a heavy pruning in August or September to encourage the roses to produce late into the fall.

Peggy Harris can be reached at or by calling P.M. Harris Landscape Design at 805.986.6965.