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Fertilizing Nursery and Floral Crops

Proper nutrition is one of the most critical factors in the production of nursery/floral crops. Generally speaking, most of these plant materials may be classified as "heavy feeders", requiring relatively large quantities of fertilizers. However, the ratio and sources of elements supplied are as important as their amounts.

Research has shown that the balance between nitrate (NO3), nitrogen (N) and ammonium (NH4) can effect plant growth. In Texas it is recommended that no more than 50% of the N supplied should be in the NH4 form. Increased amounts of NH4 in the growing media may result in severe ammonium toxicity of foliage burn.

Most Texas growers currently incorporate superphosphate into their growing media as a source of P. However, because superphosphate is relatively insoluble, the amount of P released during the growing season is often not sufficient.

Some growers also supply phosphorus (P) in the form of phosphoric acid (H3PO4). This is done both to supplement P nutrition as well as to help acidify alkaline irrigation water. .

Potassium (K) is a key element in maintaining poinsettia nutrition. At present most growers supply K in the form of potassium nitrate (KNO3). This material which contains both K and NO3 is an excellent fertilizer for use on potted crops. Research has also shown that a 1:1 balance between N and K2O is optimum.

Another important aspect of nursery/floral crop nutrition involves the secondary elements calcium (Ca) and magnesium (Mg). Due to continuous leaching during irrigation, these nutrients can run in short supply late in the growing season.

Most fertility programs designed for nursery/floral crop production supply Ca in the form of calcium nitrate. However, growers using pre-mixed fertilizers are generally recommended to make some supplemental applications of calcium nitrate near the end of the growing season.

Unlike Ca, most custom mixed fertilizer solutions do not contain Mg as a principal component. For this reason dolomitic lime is frequently used, not only to adjust pH, but also as a source of Mg. Once again, due to continuous leaching during irrigation, Mg levels in the medium can become low. Under these circumstances supplemental Mg may be applied in the form of magnesium sulfate (epsom salts).

Perhaps the most commonly used method to apply fertilizer is through a nutritional regime referred to as constant fertilization. This system involves the application of soluble fertilizers at very irrigation. The most important factor in this fertilization program is to apply enough water at each irrigation to leach to pots thoroughly. This prevents the accumulation of soluble salts from previous irrigations.

Many growers also use a controlled release fertilizer in combination with a constant fertilization program. Generally speaking 4 - 6 lbs/cu. yd. of growing media (14-14-14) may be used to supplement a nutritional program. However, water quality must also be taken into consideration. Caution should be used in determining if a controlled release fertilizers are appropriate.