KC Gardens

Knockout roses are great, and here’s how to fertilize them

By Dennis Patton

Knockout rose
Knockout rose Submitted.

Roses have always been a landscape staple. Who does not love a rose in bloom?

The popularity of this timeless plant has been reinvented with the release of the common Knockout Rose. This variety belongs to a group of roses often referred to as shrub or landscape roses. It has replaced the fussier hybrid tea roses in the garden. The beauty of these roses is they bloom all season long. Proper fertilization develops strong vigorous canes that produce big, plump buds with nice flowers.

Local soils tend to have plenty of phosphorus and potassium, so the recommendation of using a balanced fertilizer such as 13-13-13 or 10-10-10 is outdated. The old recommendation was to apply about 1 cup of this type of fertilizer per plant three to four times per growing season, between mid-April and mid-August.

Newer recommendations are more environmentally friendly, as it reduces the use of unnecessary fertilizer containing phosphorus and potassium. Nitrogen, the first number on a bag of fertilizer, is the key nutrient for established roses.

Using a higher rate of nitrogen and lower amounts of phosphorus and potassium are best. Examples of fertilizers to use are 27-3-3 or 25-5-5. Instead of using the one cup rate, use only about 1/8 to 1/4 cup per plant, following the same application schedule listed above. This supplies the same amount of nitrogen as the traditional application, but does not build up high and unnecessary levels of phosphorus and potassium.

Landscape or shrub roses may really not need any additional fertilizer. These plants are more vigorous than the old hybrid tea types. As a result, they will normally flower all summer long on naturally occurring nutrients in the soil. If you like, they can be given a post-winter boost with a mid-April application to get the plants off to a good start.

For the organic growers, blood and alfalfa meal are an excellent rose fertilizer. These are higher in nitrogen while being low in phosphorus and potassium. You can apply about a cup or so each time to provide about the same rate as man-made fertilizers.

Fertilizer should be placed out and around the plant, at the drip line where the roots are found. Avoid placing the fertilizer at the base of the plant. Be careful when working the fertilizer into the soil. Do not dig deeply into the soil as this will damage the rose roots. If the plants are mulched, pull it away, apply the fertilizer and then replace. Be sure to water the fertilizer into the soil immediately after application to avoid burning and damaging the plant.

Complete these simple steps and your roses should reward you with a beautiful bounty of blossoms all summer long.