Facts About Fertilizer



Proper use of a spreader can insure that fertilizer is applied evenly. Photo courtesy: Bill Rohret.

By Helen M. Stone

There are almost as many different types of fertilizers as there are plants. Whole books have been written on soil fertility and fertilizer selection; this publication has covered the topic extensively in the past years. So assuming that you’ve done your soil tests and decided on what your plant, trees and/or turf need, how do you apply it to the best advantage?

When planting, it is often recommended that fertilizer be incorporated into the soil. This can give plants and turf a “jump start,” as the roots move into the surrounding soil. Be sure that you incorporate the product thoroughly into the soil; simply throwing a shovelful into the bottom of the planting hole can lead to burn. If you are installing sod or seeding turf, thorough incorporation is also critical. Never exceed the manufacturer’s recommendation for preplant application.

Compressed dry fertilizer (planting tabs) can also be used when planting trees and shrubs. These are generally placed about half way down the rootball an inch or two away (not directly on the rootball). In our alkaline soils, these often have trouble dissolving. There are also soluble “bags” with slow-release fertilizer that might solve this problem.

You can also find fertilizer spikes for trees that are driven into the ground. In addition, devices are available that can inject fertilizer into the soil. Keep in mind that most tree roots are in the top 12 inches of the soil, so that “deep root” feeding is usually not warranted.

Speaking of injection, for trees that are in tight situations such as sidewalk cutouts, fertilizer can be injected into the trunk. The elements are carried through the tree’s vascular system. Be sure to follow directions to the letter and the tree’s natural wound mechanisms should seal the injection holes quickly and completely.

The age-old method of fertilizer application is broadcasting. This simply means spreading a fertilizer evenly over the ground. We’ve all probably seen pictures of old-time farmers with a sack at their side grabbing handfuls and flinging fertilizers in the field. As a matter of fact, you might have employed this method yourself. While there are much better ways to broadcast fertilizer, small areas can be easily done by hand.

Crucial to the success of broadcasting is to measure properly and apply evenly. It should go without saying that over-application of fertilizer can cause plant burn, not to mention wasting money and materials. In addition excess fertilizer simply moves beyond the root zone and can infiltrate watersheds.

When in doubt, use less. You can always come back and apply any excess product if necessary, but if run out when your are only one-third of the way through your target site, that spells trouble.

Using a spreader can result in much better results, as the product is laid down evenly. There are two types of spreaders: drop style and rotary.

A rotary spreader lets the fertilizer granules fall through holes, where they hit an agitator and are distributed in a circular fashion. These are ideal for large areas, although smaller, hand-held models are available (and would probably do the job just fine for today’s smaller residential landscapes).

Drop spreaders do just that – they drop the fertilizer directly below an agitator that runs the width of the spreader. The openings that distribute the product can be made larger or smaller, depending on what you are using.

Spreader calibration is an article in itself (and has been in past issues). Visit http://aggie-turf.tamu.edu/aggieturf2/calibration/calibration.html for a step-by-step description of the process, complete with pictures, at the Texas A&M turfgrass website.

When using a spreader, be sure to walk at an even speed. When using a drop spreader on turfgrass, do the two ends of the lawn first to give yourself room to turn around. Some experts recommend that you use half the amount recommended going in one direction and then the other half going perpendicular to the first application to minimize the chance of striping.

Broadcasting has also been shown to be one of the most effective ways to fertilize trees in open areas. Keep in mind that most of the tree’s absorptive roots are located below the edge of the canopy and a few feet beyond. You will be wasting your time and product applying fertilizer right next to the trunk.

After broadcasting fertilizer, be sure to water thoroughly. This will ensure that the elements move down into the roots where they can be used to manufacture the plant’s “food.”

You can also broadcast liquid fertilizer, although this is less common. More common is “foliar feeding,” when a weak formulation is sprayed directly on the leaves of the plant. This is mostly used for micronutrient deficiencies, especially iron. Results can be fast and dramatic.

Liquid fertilizer can also be applied directly through the irrigation system. Attached downstream from the backflow control device, a reservoir of product can either be pumped into a system or use the existing water pressure to be delivered directly to the roots. Plants get a steady stream of nutrients, instead of a “feast and famine” regime. The formulation can be easily adjusted according to the plant’s needs and the time of year.

Whatever method you chose, follow label directions to the letter. If a little is good, a lot isn’t better.