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John Fulton

John Fulton
Former County Extension Director

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In The Backyard

Horticulture columns and tips done on a timely basis

Lawn Fertility and Maintenance

Posted by John Fulton -

It has been quite a year already. Temperatures in the 80s followed by an extended freeze may have done in your early seeded grass. At this time, mowing is beginning in earnest. Remember to remove no more than a third of the grass blade in any one mowing. This will reduce thatch buildup, and do away with the need to rake or catch grass.

It's time to prepare for fertilizing the lawn. To begin with, it is important to know what the numbers on a bag of lawn fertilizer mean. The bag has numbers like 26-4-7 or 13-13-13. The first number is the percentage of nitrogen in the product, the second is percentage of P2O5 (commonly referred to as phosphorus), and the third is percentage K2O (commonly referred to as potassium or potash). This means that a 10 pound bag of 13-13-13 would contain 1.3 pounds of nitrogen, 1.3 pounds of P2O5, and 1.3 pounds of K2O.

It is also important to know what type of grass you have in your lawn. When looking at nitrogen application rates, improved bluegrass varieties (such as A-20 and Delphi) need 4-6 pounds of nitrogen per 1000 square feet per year. Common bluegrass varieties (such as Delta and Park) need 2-4 pounds of nitrogen per year, and fine-leaf fescues need 1-3 pounds per year per 1000 square feet. Nitrogen should be put on at least twice per year with ideal times being the first week of May and the first week of September. Resources vary on the amount of nitrogen that may be safely applied at any one time with ranges from 1 to 1.5 pounds per 1,000 square foot maximum. Most current University information recommends 1 pound maximum per application.

Phosphorus and potassium should be applied on the basis of soil test since these nutrients are not like nitrogen, in that nitrogen does not remain stable in the soil for long periods of time. Without a soil analysis, correct applications are about 1.5-2 pounds of P2O5 and 2.5-3 pounds of K20 per 1000 square feet.

Boiling this all down to practical terms means that a lawn of mixed common bluegrass and fine fescue should have about 12 pounds of 13-13-13 applied twice a year. I realize that you will build up phosphorus levels somewhat, but not very rapidly. And, the nice thing is that phosphorus will not be lost. It will remain in the soil until needed. Another option is to apply most of the phosphorus and potassium with one application, and use one of the high nitrogen products for the other.

Lawn weed control needs to be done in a couple of weeks if you are inclined to go after the broadleaf weeds in your grassy setting. I am mentioning this now, because weeds can also be an indicator of problems. Crabgrass is often an indicator of mowing too short or watering too frequently. This is often the case when trying to establish new seed since there are bare spots, and you tend to moisten frequently. Ground ivy (creeping Charlie) is usually an indicator of shady conditions or poor drainage. Clovers usually come in when bare spots are available or there is generally poor fertility. Knotweed grows in highly compacted areas. Moss grows in areas with shade, dampness, and poor fertility. Some of these conditions may be controlled to actually control the weed problems with some cultural changes.

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