Of all flowers,
methinks rose is best."
Although the English used today is a bit different compared with that of Shakespeare's era, the sentiment is the same. Rose is America's favorite flower. However, unlike Shakespearian roses which bloomed for only a short while, hybrid tea, floribunda, miniature and many other types of modern roses have the ability to repeat flowering during the summer. We take this characteristic for granted today, but it was only in the mid 1800's that the first hybrid tea and hybrid perpetual roses which repeatedly bloomed during the summer were developed. Even though these plants have the ability to bloom again, good care is important for reblooming to occur, and in determining how prolifically a rose plant is able to bloom throughout the summer.
Roses are fairly heavy feeders, so fertilization about every six weeks is necessary, unless slow- release fertilizers with longer release rates are used. With standard fertilizers, this means an application in spring as growth begins, another as the first major flush of blooms ends, and a third sometime in the month of July. Later applications of fertilizer should be avoided in our climate, since excessive late season growth may develop which is more subject to winter injury.
The amount of fertilizer used depends greatly on the size of the plant. Specialty rose fertilizers are available from many yard and garden centers or online, and should be used according to label directions. If a common garden fertilizer such as 5-10-5 is used, about one heaping tablespoon scattered beginning about six inches from the plant and extending to 18 inches (or in a band one foot wide) is satisfactory.
If organic fertilizers are preferred, dried blood and bone meal are possible choices. They may be used at about one tablespoon of each per plant on a monthly basis, depending on plant vigor. Cattle manure that has been composted also is beneficial for roses. A two-to-three-inch application of well-rotted manure each spring will aid growth and development. Whatever the fertilizer choice, newly planted roses, however, should be fertilized lightly until they are well established.
As with other garden plants, roses need adequate water throughout the summer to perform well. The amount of water and frequency of application depends upon soil type. Soil acts as a reservoir for water. There is no benefit from applying more water than the reservoir can hold, or applying it before it is depleted. Plant size and rose type also dictate the amount of water needed.
As a general rule, apply water when the top 1 to 2 inches of soil is dry. Thorough, deep watering is important. Never give light surface applications. Water should be applied slowly enough to prevent surface runoff and long enough to ensure deep soil penetration. At each watering, soil should be soaked to a depth of at least 1 foot.
There are many methods of watering roses, with soaker hoses (or drip irrigation) being the best. Soaker hoses apply water at the base of the plant, keeping foliage dry. Prolonged wet foliage tends to worsen the infestation of foliar disease of roses such as black spot. If overhead sprinkling is the only irrigation option, water in the morning or early in the afternoon so the foliage will be thoroughly dry by evening.
Good weed control also is important to keep roses blooming. Weeds and grass compete for water and nutrients and can slow growth. Tall weeds may reduce light absorption for food manufacture and also delay the drying of leaves which may lead to increased disease problems. Prompt, shallow cultivation is the best method for removing small weeds. Roses respond well to a thick mulch, which not only reduces weed populations, but also keeps soil moist and cool.
Careful insect and disease control also is important for keeping roses growing and flowering well. In our climate, black spot tends to be the greatest disease problem of roses. This fungus disease causes dark spots on the leaves which later turn yellow and drop off. Badly infected plants may lose most of their leaves is remedial measures are not taken.
Management of rose black spot should follow IPM tactics, beginning with cleanliness. Any and all leaves that drop should be removed from the rose planting and disposed of properly. Additionally, there are a number of fungicides available to help control the disease. They include (but are not limited to) captan, chlorothalonil, copper, ferbam, mancozeb, maneb, triforine, sulfur, thiophanate methyl, and ziram. Chlorothalonil has proven itself to be effective against black spot and offers some protection from powdery mildew as well. This fungicide is available from many different companies, now that its patent has expired. If infestation is not too severe, applications about every two weeks should be adequate. If beds are badly infected, weekly applications are warranted. As with all pesticides, be sure to read and follow label directions carefully.
Systemic fungicides (e.g., tebuconazole) are available as part of rose "three in one" or "all in one" products. These formulations most often include fertilizer and a systemic insecticide (e.g., imidaclorprid) as well. The timely and proper usage of these compounds can take care of a number of rose management tasks in one easy step.
If all-in-one products are not used, insect control must be addressed using different tactics. The key to good control is first to identify the pest in question. Spider mite, thrips, rose slug, Japanese beetle and scale are common insect pests of roses during the summer months. Good sanitation and (if needed) timely applications of insecticides can help prevent the insect population from becoming a serious problem. Again, use insecticides as directed by the product's label.
Finally, a devastating disease known as rose rosette still is problematic on our cultivated roses. Also known as witches'-broom, rose rosette is caused by a virus-like organism that is spread by a nearly microscopic eriophyid (air-borne) mite. Infection occurs when a mite feeds on an infected plant, then travels to a healthy plant to feed. Early symptoms of rose rosette are rapid stem elongation followed by certain branches of the plant developing thickened, abnormally thorny stems. Then, many short deformed shoots form, often displaying a red pigmentation and smaller, misshapen leaves. At this point there is no cure for the disease and infected plants should be carefully removed from the garden and destroyed.
For additional information on rose care, please refer to MU Extension publication g6601 titled "Roses: Care After Planting" (https://extension.missouri.edu/publications/g6601) .