The amount of supplemental water needed depends on the weather and type of soil in the rosebed. The soil should be physically checked for moisture. Newly planted roses may need more water than established plants because of the loose condition of the soil. Do not allow the soil around roses to dry out during dry, snow-free winters. Supplemental watering is needed during dry winter periods and monthly applications may be necessary. Mulches help reduce moisture loss from the soil.
Pests
The major rose pests are aphids, spider mites, thrips and powdery mildew. More recently, the rose midge and rose stem sawfly (probably Hartigia trimaculata) became problems in some areas. Verticillium wilt is also known to be a problem on roses.
Insects
An application of a recommended insecticide starting when aphids first appear gives excellent control. The use of a systemic insecticide also helps control thrips and the rose stem sawfly. Spider mites can usually be kept under control by a forceful spray of water from a garden hose directed to the undersides of the leaves. A thorough washdown once a week often will give control, however, during hot and dry weather the water spray may have to be used more often. During severe infestations or because of time constraints, the use of a miticide maybe in order. If a miticide is used, often it is recommended to alternate types of miticides to prevent a buildup of resistance in the mites.
Flower thrips are tiny winged insects about 1/20 of an inch long that affect the buds and blossoms of roses and some other flowers. On bright warm days, these flying insects usually are found inside the bloom near the base of the petals. Thrips are said to prefer light colored blossoms such as yellow and white and their damage can readily be seen as discoloration of the petals. During severe infestations, some blooms will not open normally due to the insect’s damage. Sometimes a concentrated effort of misting the buds and blossoms with an insecticide such as Orthene is necessary.
The rose midge causes the tips and tiny buds of the rose stem to wither, blacken and die. A bad infestation may leave an entire rose garden without blossoms. If the midge becomes a problem, reasonable control can be obtained by the use of diazinon granules or liquid diazinon as a soil treatment and a recommended insecticide as a spray for the foliage. When damage first appears, treat all soil around the roses with 5 percent diazinon granules or diazinon liquid. When the granules are used, lightly water in. Spray the foliage and particularly the terminal or tips of the rose stems with a recommended insecticide on a regular basis for the rest of the growing season. If a severe infestation occurs, one or two additional intervals may be necessary to bring the midge under control.
Diseases
Powdery mildew, blackspot, anthracnose, rust and verticillium wilt are all caused by fungi. Powdery mildew is probably the most serious disease affecting roses. It is at its worst during periods of warm dry days and cool humid nights. Symptoms include a whitish coating on leaves and young shoots, curled leaves and distorted buds. This disease is best controlled by planting resistant varieties and a preventative spray program with a fungicide. Funginex with Triforine as the active ingredient and Benlate used as directed on the label will give reasonable control.
Pruning Established Roses
During the flowering period, it is important to remove the spent blossoms
to promote new flower shoots. Remove faded flowers by cutting the
stem to a five-leaflet leaf. Some control of the shape of the plant
can be accomplished by this pruning.
Pruning established roses varies with the different types of roses.
In general, the object is to remove all dead or diseased wood, to remove
old, weak or undesirable wood and to shape the plant.
Pruning of climbers consists of removal of dead wood and old and unproductive canes. Prune shrub roses to remove dead wood, damaged canes and weak twiggy growth. Delay removal of old canes to thin and rejuvenate shrub roses and climbing hybrid teas and climbing grandifloras until immediately after the June bloom.
Fertilizing Established Roses
A soil test to aid in setting up a fertilizing program is very helpful
and usually saves money. Take the sample for soil tests in early
spring so the results are known before the first application of fertilizer.
Fertilizing, as with pruning, should not be done too early in the spring.
Make the first application of fertilizer about two weeks after the close
or low pruning is done or about the date of the last killing frost.
Fertilize the second time during or after the second bloom, around the
middle of July in most areas.
Fertilizing late in the season may result in damage to roses if an
early freeze strikes the lush growth encouraged by the nitrogen fertilizer.
For this reason, apply the last nitrogen fertilizer no later than two months
before the first killing fall frost in your area.
Selection and application of fertilizers are an important part of rose
culture. The so-called complete plant foods, sold as all-purpose
garden fertilizers in formulas of 5-10-5, 6-10-4, or 15-15-15, are a good
choice for mixing with the soil when making new beds well in advance of
planting. The phosphorus and potassium is not readily water soluble
and moves very slowly in the soil. For this reason, it is difficult
to get these two elements into the root zone when they are applied to the
surface of the soil.
Time release fertilizers, although probably more expensive, can be a time saver since only one application per year is necessary. These fertilizers are available in more than one type, some designed to release their nutrients over shorter periods of time than others. Use care in the application of fertilizers. Misuse or higher than recommended rates of application can damage your roses.