Spring growth has started or is about to begin for shrubbery. With this growth comes the need to fertilize. Plants have to have nitrogen to grow, and they have to have time to put that nitrogen into the leaf and stem tissue so they can use it.
March is the best month to begin fertilizing shrubs, then follow with another application in May. Top off the year with a September fertilization.
By fertilizing these three times, you are copying Mother Nature. In the wild, plants recycle their waste. Leaves, berries, and spent flowers drop off and decay, thus breaking down into nutrients the plants take up and use again. It's a gradual process.
Lighter doses of fertilizer three times a year also reduce the risk of injuring plants by overfertilizing them.
We have a long growing season in Augusta, so a spring application of nitrogen will have leached out of the soil in six to eight weeks. Therefore, 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.
I don't recommend soluble fertilizers for shrubs, unless you are using them only as a supplement. Soluble fertilizers leach out of the soil much faster than granular fertilizers. You'd need to apply them much more often.
Specialty fertilizers sold for specific plants, such as azalea-camellia or evergreen fertilizers, cost more. For the most part, you don't need them. Most will have added micronutrients that are definitely needed in some areas in Augusta, and slow-release nitrogen that can be of some benefit, but a general purpose fertilizer is all you need for most plants.
Fertilizers with the timed-release pellets of nitrogen are less likely to burn and injure plant roots. The six-to -nine-month formulations can double the fertilizer's effective time, thus cutting down on the number of times you have to apply them. But don't expect the full six to nine months of active fertilizer. The high heat, humidity and rainfall of our Augusta summers release the fertilizer much faster.
On average, you can figure the fertilizer will last roughly one half the time they say it will.
Timed-release fertilizers have proved popular over the years as homeowners look for ways to save time in the landscape. But split applications of any high-nitrogen general purpose fertilizer such as 18-6-12, 16-4-8 or 12-4-4 are also safe, effective and efficient.
In March and May, an average application for established shrubs is a level tablespoon of fertilizer per foot of plant height. For plants less than a year old, use only a teaspoonful per foot. And in September, use a slightly reduced rate.
Don't fertilize during the heat of the summer: Intense heat and frequent dry spells make Augusta summers a time to maintain shrubs, not stimulate growth.
The plant's feeder roots, not the main roots near the trunk, take up the fertilizer. To best get the fertilizer to these roots, scatter it around the drip line, under the tips of the branches. The feeder roots are just beyond the drip line.
Another factor to consider when fertilizing shrubs is their size and age. If you have older, established plants that are as large as you want them to be, you might not want to fertilize them as much. You might consider just making the May and September applications, or just the one in May.
Reach Sid Mullis, the director of the University of Georgia Extension Service office for Richmond County, at (706) 821-2349 or smullis@uga.edu.
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