Extension Educator, Horticulture
Fertilizing lawns is a mystery to most homeowners. How much and when to apply? Fertilizing is an important maintenance activity to reduce weed and disease problems and generally make the lawn more attractive. Information seems to conflict. The apparent conflict stems from varying definition of a quality lawn. Some just want it to be green and not have too many weeds. While others want the "golf course" look. So first decide your category.
How much to apply? About three pounds (range of 2-4 pounds) of actual nitrogen per 1,000 square feet per growing season is suggested for most full-sun lawns (Kentucky bluegrass; Kentucky bluegrass mixed with perennial ryegrass and/or fine fescue). The three pounds should be split into two or three applications, with each single application of nitrogen being about 1 pound per 1,000 sq. ft. About half as much nitrogen is suggested for shade lawns.
Ok your eyes may glaze over at this point as math enters into the picture but hang in there. First you need to know the percent nitrogen in the fertilizer bag. This is always the first number listed on the bag as in 15-5-10. This is the percent by weight of nitrogen and in this case its 15% or .15. Now figure the square foot size of your lawn by multiplying the length by the width. Ok still with me?
a. Divide rate of nitrogen desired by percent nitrogen in bag (using the decimal form).
b. Multiply answer found by square footage of lawn and divide by 1,000
EXAMPLE: 15-5-10 fertilizer (which is 15% nitrogen), your lawn is 7,000 sq ft, and you want to apply 1 lb. nitrogen/1,000 sq ft. If the train leaves the station at 2:00PM (oh sorry had a math class flashback).
a. 1 lbs. divided by .15 = 6.66, round to 6.7
b. 6.7 multiplied by 7,000 = 46,900; divided by 1,000 = 46.9, or 47 pounds
Therefore, need about 47 pounds of 15-5-10 fertilizer to cover entire lawn.
After calculating how much to apply, when to apply is the other important decision. The schedule below outlines when to apply based on how many applications are to be made annually and the quality of lawn desired. Use controlled-release nitrogen fertilizers in May and September and a fast-release source in late fall.
One application "Just want it to be green and sort of healthy": Apply in early September (around Labor Day).
Two applications: early May (Mother's Day) and early September (Labor Day).
Three applications: early May (Mother's Day), early September (Labor Day) and late October/early November (Halloween)
Four applications for high quality lawns: (only if irrigating in summer) early May (Mother's Day), mid-June (Father's Day) early September (Labor Day) and late October/early November (Halloween).
All this great information about lawns and much more can be found on University of Illinois Extension website.
New publication, Pocket Guide to Good Gardening was designed for easy use and speedy reference. Topics include: care and selection of plants; reading pesticide labels and controlling pests. Cost is $5 contact your local U of I Extension office or call 1-800-345-6087.
Glorious Gourds program at the Master Gardener Idea Garden on South Lincoln Avenue at the U of I Arboretum on October 19 at 10:00 am. Learn all about growing, harvesting and using gourds.
Home composting class on October 22 at 7:00 p.m. and repeated October 24 at 1:30 p.m. through the teleconference system at U of I Extension Champaign County office at 801 North Country Fair Drive in Champaign. No charge but registration is required. Call U of I Extension at (217) 333-7672.