Roses need light, air and water, so plant them where they will get at least six hours of sunlight a day. When watering, make sure they get one to two inches. During a hot summer, a rose can take up four to five gallons of water a week. Water every four to seven days.
The answer to a question about pruning roses depends on the type of rose as well as the conditions. It is safest to grow shrub roses, which need very little pruning other than for maintenance.
Don’t prune in fall, but wait until spring and begin pruning just when the sap is starting to rise in the shoots. Another way to determine the right time is to look for swollen buds on native shrubs. For shrub roses, it is only necessary to cut away any dead or diseased wood. If the bush is old and dense, you can prune away some of the shoots on the inside to promote air circulation. Prune away any thin, weak shoots. Be sure to cut on the diagonal just above an outward facing bud. If your rose is an “own-root” rose, meaning that it has not been grafted to some hardier root stock (as most hybrid teas are), it can grow new canes fairly quickly even if it has died or been pruned right back. Make sure your pruners are clean and sharp. Some people recommend sealing cuts larger that 1/4 inch with nail polish to prevent infection.
For someone who has been plagued by black spot or mildew, spraying the plant and the ground around the rose with dormant oil in early spring will help kill the bacteria. Make sure you apply fresh new mulch as well. Roses like a slightly acid soil with a pH of about 5.5 to 6.5, so mulching with peat moss, which can promote acidity, is okay. Mulch should be about two inches thick and not pile up around the stems.
To prevent black spot and powdery mildew, spray the leaves, especially the undersides, with a commercial fungicide or with a mixture of one tablespoon of baking soda and a few drops of a mild dish detergent to a gallon of water.
Roses also need fertilizer, but too much nitrogen can inhibit blooming. Roses like a higher percentage of phosphorus so look for a 5-10-5 or a 4-8-4 fertilizer. You can use a granular fertilizer, scratching about one heaping tablespoon per plant into the ground about once every six weeksbefore watering. Start as soon as all frost has left the ground.
Bone meal, liquid fish fertilizer and manure are good organic fertilizers. Sea Magic is beloved by roses. It promotes lush foliage and bigger blooms.
Roses need iron. Powdered chelated iron can be mixed with liquid fertilizers and applied once a month for greenest foliage. Where the soil is very alkaline, using Epsom salts which contain magnesium sulphate will help neutralize the soil. Apply a tablespoon per rose every four to six weeks, either by sprinkling it around the rose or by adding it to liquid fertilizer. You can buy alfalfa as pellets. Apply a handful around roses about three times over the growing season and water in well. Alfalfa is high in protein, vitamins and minerals and fixes nitrogen. It also contains triacontanol, a growth stimulant.
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