Typical Poor Soil
Poor soil is thin and fine. It is often compacted, the air compressed from it by pressure from foot traffic, repeated mowings, and pounding rain. Lacking the spongy organic matter, or humus, that gives soil texture and substance, it does not retain moisture well. It does not drain well either. The absence of organic matter virtually guarantees that it does not have any nutrients in it.
Most importantly, poor, compacted soil has no air to support microlife. The “life” in soil--the various macro and micro organisms that enrich soil by creating and processing nutrients in it--require organic matter to survive, so they are not present or active in poor soil. It is basically dead, sterile. Therefore, your grass plants are entirely dependent on you for their nutrition--including the critical 4 pounds of nitrogen per 1000 square feet each year.
Poor Soil Requires More Time and Fertilizer
If your soil is poor, it can not nourish grass plants. Your grass depends entirely on you for sustenance. Since the average lawn in America needs 4 pounds of nitrogen per 1000 square feet per year, never more than 1 pound at a time, you must fertilize 3 or 4 times a year to keep the grass happy. If you use slow-acting fertilizer three applications will probably do the job. If you use the less expensive quick-acting fertilizer, then four applications are definitely needed.
Calculating the Correct Amount of Fertilizer
Check the package label: Labels on granular lawn fertilizer bags indicate the size of the area their contents are intended to cover. Most products are packaged to cover 5000 or 10,000 square feet. Consequently, you need to have a rough idea of the size of your particular lawn.
Measure your turf area: Pace off the dimensions of each turf area and multiply the length times the width. For instance, a front yard that is 24 by 40 feet is 1000 square feet. To estimate how much fertilizer to buy, total the square footage of all of your lawn areas. An alternative is to measure the boundaries of your property to determine its square footage; then estimate how much space your house, gardens, and other non-turf areas take and subtract it from the total.
Buy more than necessary: Even if you accurately measure your lawn and purchase the correct amount of fertilizer, you will probably need a bit more. It is difficult to spread granular fertilizer uniformly and thinly so that it covers the area advertised on the bag. Any unused product will keep until next year.
Compensation Fertilization of Lawns
If your soil is poor and compacted with minimal organic content, plan to feed the lawn three or four times over the season. Because the soil can’t support large populations of earthworms and microbes which normally generate nutrients, you must deliver enough nutrition to keep the grass going yourself.
Slow-acting fertilizer products indicate on their labels how long the nitrogen is released into the soil. It may be 6, 8 or 10 weeks. Time your applications according to that time frame, aiming for early spring, late spring before the heat sets in, late summer (if you plan 4 applications), and late fall before the ground freezes. Also, plan to leave the grass clippings as you mow all season.