Lawn Dethatching & Fertilization

April 7, 2016 – Kenosha News

LawnQuestion: Do you believe spring power raking/thatching is good for the lawn. I had it done last year in the spring and had problems with weeds afterwards. What about fertilizers? Are some brands better than others? C.M.

Answer: I don’t recommend power raking, also called dethatching or vertical mowing. Power raking tears up the lawn damaging its appearance and creating open spaces for weeds to grow. Dead grass blades and winter debris are best managed by hand raking in spring. Throw the dead grass and leaves you rake up into your compost pile.

If thatch is a problem in your lawn, aeration and topdressing is the best way to go. Thatch is a build-up of living and dead grass roots and stems between the soil and green grass blades. Check the thickness of your lawn’s thatch layer by cutting three to four inches down into the grass with a shovel and lifting up a piece of sod. Thatch looks like a thick tangle of brown roots lying on top of the soil. Aeration is needed only when the thatch layer is over one-inch thick or the soil is compacted. Aerate in May or September when turfgrass is actively growing. Lawn or core aerators can be found at rental places for do-it-yourselfers or a lawn care company can do the job for you. (Walking over the lawn with spiked shoes doesn’t work.)

If the thatch layer is thick or your lawn is uneven, you should topdress after core aerating. Use a drop spreader to distribute a thin layer (1/8 to 1/4 inch) of soil or compost over the lawn. Topdressing adds microorganisms that help breakdown thatch and smooth the lawn.

Brand is not important in choosing a fertilizer, but a product should contain 25 to 50 percent slow release or controlled-release nitrogen. Typical slow-release formulations in synthetic lawn fertilizers are ureaform, sulfur-coated urea, IBDU, and water insoluble nitrogen (WIN). Non-synthetic and organic fertilizers are slow-release because they require the actions of microorganisms to release nitrogen and other nutrients. These products are lower in nitrogen per pound but slowly build nitrogen stores in soil organic matter when applied twice per year.

Lawns less than 10 to 15 years old should be fertilized three times a year in late May, early July, and early September. Skip mid-summer application if your lawn in over 10 to 15 years old and has been regularly fertilized, or if you leave the clippings on the lawn, or if you allow the lawn to go dormant by not irrigating in summer.


Kenosha County UW-Extension LogoBarb Larson is horticulture educator for the Kenosha County University of Wisconsin Extension. She holds a master’s of science in horticulture from the University of Wisconsin-Madison. If you have a plant or gardening question, email her at or call 262-857-1942.