Published on 03/04/99

It's Time for Your Shrubs' 'Breakfast'

plants.JPG (37991 
bytes)Shrubs need three square "meals" a year, says a University of Georgia expert. It's time for "breakfast" now.

When to fertilize

"Shrubs are about to start spring growth," said Mel Garber, an Extension Service horticulturist with the UGA College of Agricultural and Environmental Sciences. "Plants have to have nitrogen to grow. They have to have time, too, to put that nitrogen into the leaf and stem tissue before they can use it."

If you're waiting for the best time to fertilize your shrubs, Garber said, wait no more. "If you haven't already done it," he said, "now is the best time."

Follow up with a "lunchtime" application in May. Then top off the year with a lighter meal in September.

Nature's fertilizing cycle

In the wild, Garber says, plants recycle their food. Leaves, berries and spent flowers drop off and decay, breaking down into nutrients the plants' roots take up and use again. It's a gradual process.

Lighter doses of fertilizer three times during the year also reduce the risk of injuring plants by overfertilizing them.

Nitrogen leaches quickly

But the main reason for the three-meal approach is that nitrogen, the key element for growth and color in plants, doesn't last very long around shrubs. What the plants don't use, the rain fairly quickly washes, or "leaches," out of the soil.

"We have a very long growing season," Garber said. "A spring application of nitrogen will have leached out of the soil in six to eight weeks. So we make small applications. We use and lose that nitrogen, then come back with another small application."

The idea is to put only as much nitrogen into the soil as the plant can take out in a few weeks. That saves fertilizer and money. It also keeps the excess nitrogen out of the groundwater.

Choose the right type of fertilizer

Garber doesn't recommend soluble fertilizers for shrubs in the lawn. Soluble fertilizers are in a quickly usable form, he said, but because of that form they also leach out of the soil much faster than granular fertilizers. You'd need to apply them more often.

Specialty fertilizers sold for specific plants, such as azalea-camellia or evergreen fertilizers, cost more. And you don't really need them. "A general-purpose fertilizer is all you need for most plants," Garber said.

Fertilizers with timed-release pellets of nitrogen, though, are less likely to injure roots, Garber said.

Time applications carefully

The six- to nine-month formulations can double the fertilizer's effective time. But don't expect the full six to nine months of active fertilizer. The high heat and humidity of Georgia summers release the fertilizer faster.

Timed-release fertilizers are popular. But split applications of any high-nitrogen general-purpose fertilizer such as 18-6-12 or 12-4-4 are also safe, effective and efficient, Garber said.

In March and May, a normal application for established shrubs is a level tablespoonful of fertilizer per foot of plant height. For young plants, use only a teaspoonful per foot. And in September, use a slightly reduced rate.

Don't fertilize during the summer. Normally intense heat and frequent dry spells make Georgia summers a time to maintain shrubs, not stimulate growth.

Put fertilizer in the right place

The plant's feeder roots -- not the thick main roots near the trunk -- take up the fertilizer. To best get the fertilizer to these roots, scatter it around the drip line, a line under the tips of the branches. The feeder roots, Garber said, are just inside to just beyond the drip line.

Dan Rahn is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.