Pensacola News Journal

For: Saturday, April 5, 2003

By: Daniel E. Mullins

Extension Horticulture Agent

Santa Rosa County

Supplemental Fertilizer Helps Annuals to Flower All Summer Long

Do you plant flowering annuals in the spring only to see them bloom a little before fizzling in June? In many cases, a few light applications of fertilizer during the spring and summer could make a world of difference.

Sandy coastal soils do not have the ability to store certain nutrients, particularly nitrogen and potassium. Since these 2 nutrients are unstable in most flower beds, supplemental applications are usually required for flowers to grow and bloom over a long period of time.

Keeping nitrogen and potassium at an optimum level can be accomplished using one of several different forms of fertilizer. First, look for a product that is low in the middle number, which is phosphorus. This nutrient is very stable in our soil and once enough is present, high phosphate fertilizers should be discontinued. In fact, the repeated use of high phosphate materials can eventually tie up or reduce the availability of other nutrients.

Fertilizer products with a ratio of 1-0-1 are generally recommended for supplemental applications on sandy Gulf Coast sites. This is a ratio of nutrients in the fertilizer, not the actual analysis. For example, a fertilizer with an analysis of 15-0-15 or 20-0-20 would have this ratio of nitrogen to potassium.

There are several forms of fertilizer that can be used for supplemental application. The plants don’t care as long as the right fertilizer analysis is used, if it is applied at the right time and at the right rate. Slow release products are available that supply a more constant nutrient availability over a longer period of time. Though generally more expensive than standard dry, granular fertilizer only one or two applications can last for the entire growing season.

Liquid or soluble fertilizer products can be used. Read labels before choosing one. There are some with the more desirable 1-0-1 ratio on the market, but these are not as readily available as those with high levels of phosphorus.

Some soluble fertilizer labels contain mixing rates for either leaf feeding or root feeding. For supplemental applications, use the mixing rate recommended for root or soil application. Enough should be mixed with water to thoroughly soak the soil around each plant. Applications to leaves, sometimes called foliar feeding, might provide a brief green-up but does not substitute for applying fertilizer to the soil.

The use of standard granular fertilizer such as 15-0-15 or 15-0-14 is also an acceptable to supplement nitrogen and potassium in flower beds. This product is usually available in a quick release form and is subject to burning plants if not used properly. Do not use more than one pound per 100 square feet of area and be certain to water thoroughly after applying.

Organic gardeners can supplement with one of the organic meals processed from cottonseed, soybean or alfalfa. In order for nutrients to be available, these organic fertilizers should be applied about 3 weeks before the estimated time that they will be needed by the plants.

The principle is to keep nitrogen and potassium available at a uniform, constant level without applying excessive amounts. This can be easily accomplished by carefully choosing a fertilizer and applying it at the right rate. The frequency of application will depend upon the form of fertilizer used. The quick release or soluble forms might require monthly application.