Question: We are getting confused about which lawn fertilizer to use. What is the difference between quick and slow release nitrogen?

Answer: In order to keep your lawn vigorous and healthy, WSU Extension turfgrass specialists recommend applying nitrogen fertilizer four times a year. The application times are easy to remember since they correspond with these holidays: Easter, Memorial Day, Labor Day and Thanksgiving. The recommended rate is one pound of actual nitrogen fertilizer per 1,000 square feet of lawn area. 

Nitrogen fertilizers can be divided into two groups. One is “quickly available” or water soluble, and the second is “slowly available, “water insoluble,” or sometimes referred to as “controlled release.” With quick release fertilizers all nitrogen is released immediately and therefore available to plants provided there is adequate soil moisture. In addition, these materials are generally less expensive, can cause rapid grass growth, have short soil residual, can leach and have high burn potential. Urea, ammonium sulfate, and ammonium nitrate are all examples of quick release fertilizers.

Slow release fertilizers on the other hand, provide nitrogen over a longer period of time. Because nutrients are released at a slower rate throughout the growing season, plants are able to take up most of the nutrients without waste by leaching. A slow release fertilizer is more convenient, since less frequent application is required. Fertilizer burn is not a problem with slow release fertilizers – even at high rates of application; however, it is still important to follow application recommendations. Slow release fertilizers may be more expensive than soluble types, but their benefits outweigh their disadvantages. They include products like IBDU, sulfur-coated urea, ureaform, and polycoated fertilizers. Slow release products are more expensive to use, but turfgrass growth and color are more uniform over a longer period of time than with quick release types.

Quick release fertilizers can result in growth spurts with a lag period between applications. A mixture of the two types of products may yield the best results. These are called “bridge” type fertilizers. Check the label to see what form of nitrogen is used to determine whether fertilizer is quick or slow release or a combination. In areas that are close to sensitive water sources or on very sandy soils, it would be best to use a slow release form of nitrogen or small amounts of quick release fertilizer at more frequent intervals.

Question: How much thatch is too much? Our lawn has never been thatched and we are thinking of getting a thatching blade attachment for our lawn mower to do the job. 

Answer: A layer of thatch 0.5 to 0.75 inch is generally acceptable in home lawns, but anything greater can begin to cause problems.

Once a thick layer of thatch has formed, it must be removed by vertical mowing. Use a machine that has rigid or flexible blades or tines (power rakes) that can cut into or pull turf out of the soil surface. If deep thatch layers are to be removed, do not try to do so in a single pass, but make repeated passes in different directions and lower the thatch machine at each new pass. You can rent a power rake, or you can hire a professional lawn service to do the job. Attachments to your lawn mower are not as effective as true vertical mowers.

The best time to dethatch in our coastal area is spring or fall, which usually means mid-March through early May, or mid-September to mid-October, weather permitting. Dethatching during these times will allow the grass sufficient time to recover before stress of summer heat or winter cold. However, in some cases it may be necessary to reseed the lawn after heavy thatching, which may result in thin or bare areas. Overseeding is accomplished by using half the seeding rate recommended for establishment of the lawn.

Once a thick layer of thatch has been removed, dethatching every year or every other year will ensure a healthy lawn that is easy to manage. Dethatching is less disruptive and lot less work if it is done regularly. 

EDITOR’S NOTE: For answers to local gardening questions go to (www.pnwmg.org) or call 360-249-4125, the WSU Extension office in Elma, or call Rachel Gana at 642-8723 or acornwp@yahoo.com.