Rose (Rosa spp.) enthusiasts vary widely on rose fertilizing regimens, but most agree that roses benefit from regular feeding. When to fertilize and forms to use depend on your garden's location, the time of year, types and ages of roses and your rose-growing goals. With rose varieties hardy from U.S. Department of Agriculture plant hardiness zones 2 through 11, most mature roses flourish with added nutrients. Better resistance to disease, stress and pests is common -- along with more blooms. Timely feedings with complete fertilizers generally provide all the nutrients most roses need.
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Granular fertilizer can be harsh on young, newly planted roses. During their first year, an organic, liquid fertilizer, such as fish emulsion, can be applied to roses' soil to provide safe, gentle nutrition. One 2-4-0.5 fish-emulsion plant food manufacturer recommends mixing 1 tablespoon of the fertilizer with 1 gallon of water, and applying it each month of the growing season. Established plants handle complete, balanced granular fertilizer. A 6-12-6 or 6-8-6 granular fertilizer applied every four to six weeks during the growing season provides nutrition for most ground-planted roses. For example, work 1 cup of 6-8-6 granular rose food lightly into the soil around each rose bush, 6 to 8 inches from its trunk. Wear protective clothing, including safety eye-wear, when working with any fertilizer. Water before and after you fertilize so nutrients become soluble and available to the plants.
Time of Year
Look to your roses, not the calendar, to schedule the year's first feeding. Wait until roses have 4 to 6 inches of new growth and at least one complete leaf with five to seven leaflets. Letting your roses signal their readiness for fertilizer helps protect them against damage from late-spring frosts. In cold climates, stop applying all fertilizers six to eight weeks before the season's first average annual hard frost. Fertilizing after that time stimulates new growth that delays dormancy, reduces cold hardiness and increases chances of winter damage. Avoid using high-nitrogen fertilizers in particular. Southern gardeners have a different schedule. In northern Florida, for example, gardeners feed roses from February to November while southern Florida gardeners fertilize year-round.
Types of Roses
Not all roses benefit from added fertilizers, even when the plants are fully established. Old-fashioned, species-type and rugosa-type roses thrive with little or no fertilizer, or with very gentle organic options, such as fish fertilizer applied at the same rates as for first-year roses. Avoid liquid synthetic fertilizers; their quick-release chemicals burn these roses. Many of these shrub types also bloom just once per year, and healthy soil alone supports their blossoms and their health. The heavy flowering of modern repeat- or ever-blooming types of roses depletes soil nutrients, however. Those roses' health and continuing blossoms require regular nutrient boosts. Miniature roses need proportionately less fertilizer than common roses. Large climbers do best with more fertilizer than non-climbing roses receive.
Many rose growers choose to add an annual dose of Epsom salt, chemically known as magnesium sulfate, as rose growth renews in spring. It is applied to the soil at a rate of 1/3 to 1/2 cup per bush. Epsom salt's magnesium increases bloom production and enriches flower and leaf color. Container-grown roses benefit from liquid fertilizers; frequent watering leaches granular fertilizer out of pots before it fulfills its purpose. Warm-climate gardeners feed roses one-half-strength fertilizers during summer months for the same reason. Roses prefer soil pH in the 6.0 to 6.5 range. In areas with alkaline soil, rose bushes may need more nutrients or more frequent fertilizer applications to get amounts they need.