With this new growth on plants comes the hunger for food thus 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 always the optimal month to begin fertilizing. Then it is good to follow-up your March application with another one in May. Then top off the year with a September fertilization.
By fertilizing these three times, we 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’ 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. But the main reason for the three times 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 quickly washes away, or leaches out of the soil.
We have a very long growing season in , 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 (liquid) fertilizers for shrubs, unless you are only doing it as a supplement. Soluble fertilizers are in a quickly usable form, but because of that form, they also 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 and are great, but for the most part you don’t need them. Most will have added micronutrients (that are definitely needed in some areas in and around ) 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, though, 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 summers release the fertilizer much faster. On the average, you can figure that they will last roughly one half the time they say they will.
Timed-release fertilizers have become more and more 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, a normal application for established shrubs is a level tablespoon of fertilizer per foot of plant height. For young plants of less than one 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. Normally intense heat and frequent dry spells make 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, a line under the tips of the branches. The feeder roots are just beyond the drip line, unless of course, it is a newly planted shrub.
There are many different organic fertilizers you can use, that are good and that break down slower so they will feed your plants for a longer period of time. Options on shrubbery include different animal manures, compostost, Harmony Ag (chicken manure based), rock phosphate, and green sand (for potassium).
Another factor to consider when fertilizing shrubs is the size and age of them. If you have older established plants that are as large as you want them to be, then you may not want to fertilize them as much. You may consider just making the May and September applications, or just the May one.
Reach Sid Mullis, the director of the University of Georgia Extension Service office for Richmond County, at (706) 821-2349 or firstname.lastname@example.org.