Answer: The best way to develop a fertilization program for roses is to test your soil and then fertilize based on the test results. Otherwise it is difficult to give more than a general guideline.
An annual topdressing in spring and fall of good quality compost plus a year round layer of organic mulch is a good beginning to feeding the soil. You could also use a slow release general purpose fertilizer such as 10-10-10 per the label directions, during the growing season of spring through late summer. Do not fertilize in the fall. It is actually better to underfertilize than overfertilize, so do not assume more is better.
Epsom salts is sometimes used in areas where there is a lack of magnesium in the soil. A small amount, maybe a half a cup per bush, sprinkled around the drip line is all you would need. Your local professionally trained nursery staff should be able to tell you if that is a recommended supplement in your local soils, or not necessary.
In addition to fertilizing, keep in mind that healthy roses require a minimum of six hours a day of direct sun, evenly moist but well drained soil, and good air circulation along with pruning suited to the type of rose you are growing. It also pays to select disease resistant roses known to grow well in your local area.
Finally, let your roses be your guide. If they are blooming well and healthy, your fertilization is adequate. I hope this helps.
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