To successfully grow hybrid tea roses in Iowa, gardeners must give them considerable care. Important cultural practices during the summer months include watering, fertilizing, deadheading, and pest control.
Hybrid tea roses require watering during hot, dry weather. The actual amount and frequency depend upon weather conditions and soil type. In most gardens, a deep soaking every two weeks is sufficient. Soak the soil to a depth of 10 to 12 inches, applying the water directly to the soil. Overhead watering wets the foliage and increases disease problems. If overhead watering is unavoidable, the best time to water is during the morning. This allows the foliage to dry quickly.
A mulch around the roses helps to conserve soil moisture and control weeds. Possible mulches include wood chips, shredded bark, pine needles, and cocoa bean hulls. Spread 2 to 4 inches of mulch around the base of each plant or over the entire bed.
To encourage healthy, vigorous growth and abundant bloom, fertilize hybrid tea roses three times a year: first, in early spring immediately after pruning; second, during the first bloom period; and third, in mid to late July. Do not fertilize after July 31 because it may produce succulent new growth that may not harden sufficiently before winter. A general purpose fertilizer, such as 10-10-10, should produce excellent results. Apply 1/4 cup evenly around each plant, lightly cultivate the fertilizer into the soil, and then water thoroughly.
Removing spent flowers will conserve the plant's energy and encourage repeat bloom. The procedure for deadheading roses during the first growing season differs from established roses. On a recently planted rose, remove the faded flower above the uppermost three-leaflet leaf. Removing a large amount of foliage reduces the plant's food manufacturing capacity and may weaken it. When deadheading established roses, cut the stem back to a five-leaflet leaf. Retain at least two five-leaflet leaves on each shoot. Use sharp tools (hand shears or knife) to remove faded flowers. Cut about 1/4 inch above the leaf with the cut made parallel to the angle of the leaf.
Controlling Insects and Diseases
Continue a rigorous spray program through the summer months to control insect and disease pests. Combination sprays that include an insecticide and one or more fungicides are available in garden centers and nurseries. Disease problems are most severe during periods of rainy weather. The key to disease control is prevention. Begin applying fungicides before symptoms appear and reapply as directed on the label. Spray both the upper and lower leaf surfaces to prevent disease infection.
While hybrid tea roses require considerable care, the results can be strikingly beautiful.
This article originally appeared in the June 9, 1995 issue, p. 83.