In natural areas, generally little need exists for supplemental fertilizer. Trees and all other kinds of plants grow to maturity using the residual minerals in the soil for their growth processes. As they grow, they use these minerals along with the available water and, by means of sunlight, manufacture simple sugars to maintain the plant, develop flowers and the seeds of reproduction.
Many plants upon reaching maturity die in place while perennials that drop their foliage during the winter months cover the soil with enriched organic matter.
As these discarded plant parts decay, they return the captured nutrients to the soil and the process starts all over again.
Such is not the case with fields, gardens and flower beds where the various crops are harvested and those captured nutrients are taken away as food for humans and other animals. When this procedure is repeated year after year, the soil becomes depleted of these minerals and supplemental fertilization is required if plants are to thrive and produce abundantly.
Poor fertilization practices are frequently the reason for unacceptable plant performance. Bad placement of the fertilizer used, application at the wrong time, using too much or too little and not choosing the proper fertilizer for the plants involved are all reasons plants fail to perform up to expectations.
For example, mixing fertilizers designed for use on farm crops (or for a lawn) into the soil when planting a tree or shrub on the day of installation can result in a plant that struggles or, ultimately, to a dead plant caused by fertilizer injury.
One solution to this problem is to use slow-release fertilizers or starter solutions that are very dilute in concentration, both of which will circumvent the salt problem.
Trees and shrubs planted now and those that were planted a bit earlier may have an additional light application of an appropriate fertilizer again in late spring or early summer and this may be repeated in late August and early September.
Do use fertilizers that contain low amounts of nitrogen for the fall application.
Major fertilization should be delayed a year from planting and remember the younger and smaller the plant, the less fertilizer it can tolerate. As the plant grows, fertilizer may be gradually increased until the maximum recommended for that species is reached.
When fertilizing flower beds and vegetable gardens, regular, farm-type (granular) fertilizers may be mixed in the soil at the time of planting, but it's best to do this a few days in advance.
If a mistake is made in these cases, remember we are dealing with relatively low value plants that will be gone anyway by the end of the growing season.
Nearly all of the fertilizer materials that you buy will contain the three major elements: nitrogen, phosphorus and potassium.
Some specialized products may also contain smaller amounts of magnesium and sulfur. You can also buy small quantities of trace element mixes if a soil test reveals that some of these are low or missing.
Relationships between the major elements in a fertilizer are important and can seriously affect how well plants grow.
Nitrogen promotes rapid growth of the vegetative portions of the plant, but an excess applied too early can result in delayed flowering and fruit formation.
Too much phosphorus can cause problems of a different kind, but the correct amount favors healthy flowers followed by good fruit production. Potassium plays a major role in root development.
Unless a soil test shows otherwise, a 1:1:1 ratio is usually best for landscape use or for leafy and root type vegetables in the garden.
Good examplese are 8-8-8, 12-12-12, etc. Other vegetables and flowers do well with 1:2:2 and 1:3:3 ratios such as 6-12-12, 10-20-20 and 6-18-18.
Joe W. White is a retired Extension horticulturist with the LSU Agricultural Center. Write him in care of The Times, P.O. Box 30222, Shreveport, LA 71130-0222; or email firstname.lastname@example.org. Please include a stamped, self-addressed envelope for written replies.