Rose fertilizers are available in both synthetic and organic forms, and in many chemical formulations. The fact is, there is no one rose fertilizer that will work for all roses. The condition of the soil in your rose garden has the greatest effect on the plant, and fertilizer should complement the pH balance and the nutrient deficiencies in the soil in each gardener's particular site. One soil amendment that should be included in most rose garden soil improvement programs is magnesium sulfate, commonly known as Epsom salt.
Magnesium is a mineral that benefits plants in several ways. It is necessary for good seed germination. Both magnesium and sulfur are necessary for the production of chlorophyll, used by plants to produce food from sunlight. Both elements make the major plant nutrients---nitrogen, phosphorus and potassium---more available and more effective when absorbed by roots.
When and How to Apply
Early in the spring, apply Epsom salt to roses at a rate of one tbsp. for each foot of plant height, with repeat applications every two weeks. Use this dissolved in water, or mixed into the soil's surface around each plant before watering.
When setting out new bare-root rose bushes, soak the plants in a bucket of 1/2 cup Epsom salt per one gallon of water for several hours or overnight to revitalize the roots. Add one tbsp. of Epsom salt to each rose planting hole, mixing it with the soil.
Healthy established rose shrubs will benefit from 1/2 cup of Epsom salt scratched into the surface of the soil around the plant base in the spring. Use an Epsom salt solution as a weekly pesticide spray; a suggested rate is 1/2 cup per gallon of water.
When rose canes droop, or cane and flower production drops or ceases altogether, the first reaction of many growers is to fertilize. While this may help, the addition of Epsom salt will help even more. Epsom salt makes the nutrients more readily available to the rose roots, and enables the rose plant to more effectively use the nutrients.
Epsom salt has been a standby treatment used by rose growers for decades. When used in the soil around the plant, magnesium sulfate will increase the number of basal canes, which are the new canes growing from the base of the rose bush. It promotes healthy foliage. Epsom salt also increases the number, size and color of the flowers on the entire plant.
Epsom salt is inexpensive. It is readily available at any drugstore or discount store.
If your soil pH is on the acidic side, use Epsom salt carefully. The sulfur is acidic, and it can speed up the breakdown of nutrients in the soil, allowing them to leach away before they can be used by the rose. Use lots of compost and a good soil-enrichment program, and leaching should not be a problem.
Most plants, including lawns, shrubs and trees, benefit from Epsom salt. Watch where runoff from Epsom salt watering goes, however. Some plants, such as sage, will not tolerate Epsom salt.