Lawns Don't Need Expensive Fertilizers

Q. I was very interested in a recent article about adding ammonium sulfate to one's lawn to keep it green. Can I do this all summer long, every 8 weeks?

A. The short answer is yes. Once a year use a high-quality lawn fertilizer as one of the applications.

A good turfgrass fertilizer should be high in nitrogen (the first number), low in phosphorus (the second number) and moderate to high in the last number (potassium). Also the ideal turfgrass fertilizer would have half of its nitrogen as slow release.

The best lawn fertilizers have a ratio of nitrogen to phosphorus to potassium of 3-1-2 or 4-1-2 with most of the nitrogen available as slow release. One example would be 21-7-14 (e.g. 3-1-2). Another might be 20-5-10 (e.g. 4-1-2).  There are many others or others close to these ratios. The important part of this, for mature lawns, is high nitrogen, low phosphorus and moderate to high potassium.

The principle nutrient lawns need is nitrogen on a regular basis. Nitrogen fertilizers keep lawns green and lush. Nitrogen is the first number in the triad of numbers on the fertilizer bag.This is why fertilizers like ammonium sulfate (21-0-0), nitroform urea (38-0-0) would be good choices to use in between the more expensive fertilizers. 

Lawns require constant growth to stay healthy and look good. This growth is mowed leaving behind lawn clippings. Lawn clippings are very high in nitrogen.Clippings are removed from the lawn because they are unsightly after a mowing. However, when mowers are used with mulching blades attached the clippings are cut into very fine pieces that fall between the leaf blades and decompose. When they decompose, they release nitrogen to the lawn. When mulching mowers are used, it is recommended to skip one application of nitrogen fertilizer every year.

This was a common scene years ago. Lawns were mowed and the clippings set on the curbside waiting to be taken to the landfill. This threw one nitrogen fertilizer application away each year.

In the case of ammonium sulfate this is 21–0–0. A bag of ammonium sulfate contains nitrogen, hydrogen, sulfur and oxygen in mineral form. There is no “filler” in it. Ammonium sulfate is 21% nitrogen. The usual recommendation for lawns is 1 pound of nitrogen every 1000 square feet.

This is applied with some sort of spreader such as a drop spreader, a broadcast spreader or hose end applicator. Since ammonium sulfate is 21% nitrogen, then 5 pounds of 21-0-0 delivers about 1 pound of nitrogen.

However, I find this rate is higher than necessary and lawns do just fine at half to three quarters of this rate. This is particularly true if mowing with a mulching mower and the clippings are allowed to fall back on the lawn. 

            In about 99% of the cases we have two types of lawns out there; tall fescue and Bermudagrass. Both of these lawns require a high nitrogen fertilizer about every eight weeks. However, the timing of these applications is different.

Cool season grasses like tall fescue grow best in the cooler spring and fall months. In our climate they are fertilized 12 months of the year., usually avoiding or reducing the nitrogen fertilizer during the hottest months.

A fertilizer application at Thanksgiving is extremely important if you want a dark green lawn tall fescue through the winter. It is unnecessary for Bermudagrass.

To make it simple, I recommend applying lawn fertilizers too tall fescue on Labor Day, Memorial Day and Thanksgiving. For Bermudagrass switch the Thanksgiving application for the Fourth of July.

There is no problem applying a fourth application to tall fescue during the heat around the Fourth of July as well but it is probably unnecessary. Any application to tall fescue during the summer should be the half rate I mentioned earlier.