By Norman Winter
Horticulturist
Central Mississippi Research & Extension Center

Fertilizing our lawns, gardens and landscape plantings is one of homeowners least understood practices. Every year countless home gardeners apply fertilizer and cross their fingers for good luck.

While managing a tourist site with 61 rose gardens, I noticed a huge difference in the plants' performance based on proper fertilizing efforts. The gardens mostly had been taken care of by volunteers.

A soil test revealed that many of our gardens had toxic levels of phosphorous and magnesium. The volunteers believed high phosphorus encouraged bloom and that Epsom salts or magnesium sulfate was needed regularly for greening of the leaves.

They did not know phosphorous lingers in the soil or that a soil test could tell them what was really needed.

Depending on where you live, it is about time to fertilize your lawn. Azaleas and camellias need fertilizing right after bloom, many vegetables are heavy feeders, and pecan trees need a lot of nitrogen.

Fertilizer probably can be defined best as a substance used to make the soil or growing medium more productive. It enriches the supply of nutrients available to the plant.

There are 16 chemical elements known to be essential for optimum growth of plants. The three large numbers on bags of fertilizer refer to nitrogen, phosphorous and potassium (or potash, as it is often called).

Nitrogen produces vegetative growth and gives a dark-green color to plants. It increases yield of foliage, fruit and seed. Phosphorous stimulates early root formation and gives a rapid and vigorous start to plants. It stimulates bud-set and blooming.

Potassium, the last of the big three, is important for increasing vigor and producing strong stiff stalks. It helps impart winter hardiness in plants.

The secondary and micronutrients are also important. Calcium is part of a compound in the cell wall. Magnesium is present in chlorophyll, the green in the plants. Sulfur affects cell division and formation.

Manganese, iron, copper, zinc and cobalt influence plant growth by serving as activators or catalysts. Boron is associated with calcium use and molybdenum is essential in nitrogen use.

Many gardeners fail to understand how much fertilizer is in each bag. If the label on a 50-pound bag of fertilizer shows a formula of 10-20-10, it consists of 5 pounds (10 percent) available nitrogen, 10 pounds (20 percent) available phosphorous and 5 pounds (10 percent) potassium. If the bag has trace elements or micronutrients, they will be listed and the percentages will be much smaller.

The other 30 pounds in the 50-pound bag is made up of filler or carrier for the nutrients.

Crape myrtles need a high nitrogen lawn-type fertilizer now to stimulate vegetative growth, followed by one higher in phosphorus for bloom.

Roses need fertilizer about every six weeks from spring until late summer. Fertilize azaleas and camellias after bloom and again in six weeks. Summer flowers need fertilizing about every four to six weeks.

Look for slow-release fertilizers. They have a long residual, low burn potential and require fewer applications.

Contact your local county extension agent to get a soil test to see what you really need for the particular crop you want to grow. If you haven't practiced regular fertilization and a soil test will have to wait until next year, talk to your certified nursery professional for recommendations.