Hot Gardens Newsletter - how to grow, fertilize and prune roses

Hot Gardens Newsletter: May and June 2007

90 Fahrenheit is a turning point for hot dry gardens

Hot News. By late May TV weathercasters in the U.S. Southwest announced excitedly that the day’s temperature reached 100F for the first time this year. For those of us who garden in hot, dry climates, the important temperature is actually around 90F, the point at which many plants begin to shut down for summer dormancy. They stop growing. They stop blooming. What these plants and trees need now through autumn is regularly watering to prevent death by dehydration. If, however, you had already planted our recommended ‘summer reliables’ you will enjoy flowers in your garden through the hot summer months.

Facts from a pro about roses in the desert

Rosey Future. One of our ‘summer reliables’ is the rose. We grow them. We love them. We spray aphids off them in the mornings. We fertilize them, now and then, and cut the shrubs back in winter. And we admit that we are not rose experts.

Recently, however, we attended a lecture by Luke Stimson of David Austin Roses and learned — much to our surprise — that all David Austin Roses sold in the United States are grown in Arizona where the temperature reaches 90F on a daily basis. This makes these highly fragrant roses ideal for hot weather gardens.

David Austin rose sir edward elgar The Austin rose, ‘Sir Edward Elgar’, rose grows side by side with a Cardoon (Cynara cardunculus).

Stimson advocated our favorite practice: plant roses as part of a traditional border — not a single, isolated specimen plants, neatly separated and labeled, as we often see in public rose gardens. One benefit of planting roses as part of a perennial border is that the roots are more likely to be shaded most of the day and the rose leaves offer shade to other companion plants beside them in the border.

Smelly to humans but good for roses

About fertilizer for roses. He also revealed what fertilizer Austin roses receive in Arizona: AGED horse manure — 18 inches of it! He emphasized the “aged’ factor — fresh manure will burn the plants in a flash. If odiferous manure is not for you, ask for organic mulch which combines aged manure with other components at your local nursery. This should not be as smelly as pure aged manure and will help bring the soil into balance.

About watering. Roses like water — lots of it. And they need soil that drains well. Many areas in the Southwest have hard-as-rock clay soil so we recommend that when you plant, dig a hole at least twice as wide as the root ball to give the roots space to grow. Morning watering will help prevent diseases such as black spot.

About Pruning roses. Stimson also suggested a simple, practical pruning technique. In November or December, he said, cut your roses back to knee height — if you want a taller shrub or one to train over an arbor, cut the roses back to waist height.

In this photo Austin roses thrive against the stone walls in Paxos, Greece — definitely a hot, dry climate environment. Photo by Nick Pottinger.

To Be Fair. Other rose growers have developed roses for hot climates. The important thing about purchasing roses, or any other plants for your garden, is to inquire where they were grown originally. Any plant that spent its early months in a damp, cold climate will have difficulty adjusting or even surviving when transplanted into a desert garden. We have planted lovely specimens from an ocean side nursery only to see them whither and die within days in the desert.