To understand the timing of lawn fertilization, it is important to understand the seasonal growth pattern of a grass plant. In the spring, grasses are coming out of winter dormancy and begin rapid growth using stored energy reserves from last year. Grasses that are over-fertilized with nitrogen in the spring will spend too much of those energy reserves on leaf growth and will not have enough left over to take them through summer’s heat and drought stress. All that is needed in the spring is to supply the grass with just enough nitrogen fertilizer to prevent it from becoming chlorotic (very light green to yellow in color).
As temperatures rise in the summer, leaf and root growth start to slow. Over-fertilization at this time could be very detrimental to the health of the grass and even cause areas to die. Avoid fertilizing during the summer except to prevent chlorosis. Very light applications and use of a slo- release fertilizer will help keep the grass green in the summer without burning or damaging the lawn.
As temperatures cool and hours of light per day diminishes in late summer to early fall, grasses begin preparing for winter by sending their energy reserves to their rhizomes and roots. A fertilizer application at this time will help the plant maximize energy production and most of the engergy will be sent to storage instead of being used for leaf growth.
Table 1 gives recommendations for various grasses at various times of the year. Keep in mind that the March application may be omitted if green-up is satisfactory and a late fall application was made the previous year. In this case, a single application of 1 lb N per 1000 ft2 can be made. Use slow release fertilizers for a late fall application and on sandy soils throughout the year to reduce nitrogen leaching. Additionally, if you are using a mulching mower or otherwise returning clippings to the lawn, you may be able to cut back the nitrogen by about one fourth.
Table 1. Nitrogen fertilization schedule for home lawns. (Adapted from Colorado State University lawn fertilization extension fact sheet).
|Grass Type¹ & Maintenance Level²||Mid March – Mid April||Early May – Early June||July – Early August||Mid August – Mid September||Early October – Early November|
|Rates are in lbs of N per 1000 ft2|
|KBG – Low||1/2||1/2||none||1||1 (optional)|
|KBG – Med – High||1/2 – 1||1||none||1||1 – 2 (2 is optional)|
|Tall fescue – Low||1/2||1/2||none||1||1 (optional)|
|Tall fescue – Med – High||1/2||1||none||1||1 (optional)|
|Fine fescue – Low||1/2||1/2||none||1/2||none|
|Fine fescue – Med||1/2||1||none||1||none|
|Buffalograss||none||1/2 – 1||1/2 – 1||none||none|
|¹Grass Type: KBG = Kentucky bluegrass
²Maintenance Level: Low = low maintenance, Med = medium, High = high maintenance