How Often Should You Fertilize Knock Out Roses?

The Grower's Recommendations

• According to the Knock Out rose official website, these roses perform well even without being fertilized. However, if you choose to fertilize them, Conard-Pyle suggests waiting until the rose bush is well-established after planting and has produced at least its first flush of blooms. Knock Out roses bloom in flushes about six weeks apart, with sporadic blooms between cycles. Don't fertilize the bushes after midsummer, as that encourages tender growth that won't harden off properly before frost.

Other Recommendations

• Like other shrub roses, Knock Out roses don't require the continual fertilization program that hybrid tea roses do. Instead, many horticulture experts recommend feeding shrub roses, including Knock Out roses, once in early spring at the same time that you prune them back. Knock Out roses should be pruned back to 12 to 18 inches from soil level in early spring, just as the leaf buds are starting to swell. In sandy soils, where the nutrients leach out of the soil before the plant can absorb them, it's best to fertilize twice during the season.

The Proper Fertilizer

• Use either a balanced garden fertilizer or a specially formulated rose food on Knock Out roses. A balanced fertilizer is one with equal percentages of nitrogen, phosphate and potassium, referred to as the NPK number. Balanced fertilizers have an NPK ratio of 10-10-10 or something similar. There is no need to use a super-phosphate fertilizer, one with a much higher middle number, which is intended to push flower growth, since Knock Out roses are naturally free-flowering. A balanced fertilizer ensures that all parts of the plant receive adequate nutrition. Whatever brand of fertilize you choose, follow package directions carefully for the correct application amount.

How to Fertilize

• Apply the recommended amount of fertilizer in a circle over the root zone of the plant. Leave the first six inches around the rose crown bare, then spread the fertilizer evenly over the next 12 inches. Work it lightly into the soil and water well. Always make sure the soil around the plant roots is moist before fertilizing to avoid chemical burns to sensitive root hairs.