Established Lawn Fertilization RecommendationPosted on March 15th, 2015 by John Foegley
Your lawn is constantly renewing itself. New roots, buds, rhizomes, tillers and leaves replace the old, diseased and worn ones in a continuing process. To keep this renewal going, your lawn needs fertilizer. You’ll need to apply adequate nutrients to insure a day-to-day supply. The big three – nitrogen, phosphorus and potassium – are of most concern for a healthy lawn. Minor elementss, including iron, manganese, zinc and sulphur are usually available in satisfactory amounts, although some specialty fertilizers include small amounts to allow for unusually high pH or wet soil conditions.
All lawn soils are deficient in nitrogen, few are deficient in phosphorus, and most are deficient in potassium. Therefore, you’ll need to choose a fertilizer that is high in N, low in P and medium in K for repeat use on Hoosier soils. Choose a complete fertilizer for your lawn. A complete fertilizer contains sources on N, P and K. The label indicates the percentages, always in that order. For example: 16% total nitrogen, 4% available P2O5 and 8% soluble K2O (potash) is labeled 16-4-8. Thus, this fertilizer has a ratio of elements of 4:1:2. Some other widely available lawn fertilizers include 19-5-9, 16-8-8, 24-4-8 and 30-3-10. A note about lime: only about 1/3 of new lawns and less than 10% of established lawns need lime. If you suspect lime is needed, have a soil test done before you apply.
NITROGEN IS MOST NEEDED The amount of nitrogen applied to a lawn will regulate its growth, if all other nutrients are maintained in ample supply. Thus, rates of application are often based on nitrogen solubility and availability. However, nitrogen is easily broken down by bacteria and leaches out of the soil. So, carryover is small unless slow release forms are included. Grasses use large amounts of nitrogen. A deficiency may be indicated by a pale green color, poor growth and thinness of turf. Rapidly available ammonium nitrate, or ammonium sulphate, or ammonium phosphate, plus urea and potassium nitrate are sources of quickly soluble and available nitrogen. When used repeatedly at light rates (1/4 to 1 pound N for each 1,000 square feet) uniform growth can be maintained. Most complete fertilizers include some readily available nitrogen for economy and rapid response. Slow release, chemically prepared, Ureaform contains molecules which break down slowly under bacterial action. The 38% N Ureaform is blended or created in process for many fertilizer formulations. More than 50% nitrogen source listed as Ureaform indicates a high quality fertilizer. Another nitrogen source, IBDU (Isobutlidene diurea) provides 31% N, which is slowly broken down in water. So, by using this form, which has a larger particle, reserves can be put into the rootzone and once-a-year fertilization becomes practical. Natural organics release nitrogen more slowly through the decay process. Thus, warm, moist conditions favor nitrogen release. Activated and processed sewage sludge, animal tankage, seed meals and manures have slow solubility.
PHOSPHORUS For new plantings, adequate phosphorus should be mixed into the seed bed to encourage rapid early growth. The phosphorus needs of established turf are easily met. In fact, in many soils, particularly on golf courses, excess phosphorus has accumulated.
POTASSIUM Turf uses potassium in great amounts. Potassium is important for turf vigor, health and toughness. Not only is it leached by rains and fixed by soils, it is used in direct proportion to the amount of nitrogen consumed by the turf. As a general rule of thumb, apply half as much potassium as nitrogen. So, ratios of 4:1:2 are usually suggested for best use. In the following tables, the percentages of phosphorus and potassium in new lawn soils and established lawn soils are analyzed. You can see readily that the need is much greater in both cases for potassium, although the new lawns did require addition of phosphate materials.
WHEN – – – – – – – – – – – – – – – – — – – – – HOW MUCH – – -NITROGEN SOURCE
1st Application May 15 thru June 1st – – – – 1lb N. / 1000 sq. ft. Slow Release
2nd Application July 15th-30th- – – – — – – .75 lb N/1000 sq.ft. Slow Release
3rd Application September – – – — – – – – -1 lb N. / 1000 sq. ft. Quick / Slow Release
4th Application November 1st thru 15th – – 1 – 1.5 lb N. / 1000 sq. ft. Quick Release
Approximate ratio fertilizer of 4-1-2 is best. (Example 24-6-12)