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Mechanical dethatching (power raking or vertical mowing) removes excess
thatch buildup. However, it doesn't fix the reasons your lawn produces
too much thatch.
Using a power rake to control thatch
Thatch is an interwoven layer of decomposing grass roots, shoots and leaves that forms between the soil surface and the green top growth in established lawns. As grass sheds old roots, shoots and leaves it builds up faster than it rots...making a thatch layer.
A thatch layer is normal and can be beneficial or harmful...depending upon the amount present. Up to 1/2 inch is beneficial...over 1/2 inch needs to be addressed.
Some lawns never develop a thatch problem and others become
thatch-bound quickly. Grass type and lawn care practices influence
thatch build up.
Healthy lawns have a layer up to ½ inch thick.
It's a dense and spongy cushion...
It acts as a mulch...
Promoting microbial activity...
A good way to determine your thatch depth is to remove a two inch deep wedge from your lawn. If the thatch layer exceeds 1/2 inch, you should consider dethatching.
A thatch layer greater than 1/2 inch thick makes watering
difficult, since thatch dries out quickly and is difficult to re-wet.
As it builds up, grass roots and crowns grow into the thatch layer
making your lawn susceptible to heat, cold and drought stress.
Thatch build-up varies among lawns. Some lawns never develop a thatch problem, while others become thatch-bound within a few years. Generally, the more aggressively grass is growing, the faster it will develop a thatch layer. Build-up happens when growth exceeds rate of decomposition.
Aggressively spreading species such as bermudagrass and Kentucky bluegrass are heavy thatch builders. Tall fescue and perennial ryegrass have a low tendency for producing thatch.
Slower growers like zoysiagrass and fine fescues can form a dense thatch layer because their fibrous tissues resist decay.
Cultural practices can have a big impact on thatch.
Over watering and over fertilizing contribute to thatch buildup because they cause your lawn to grow excessively fast. Thatch is then made faster than it is decomposed.
Grasscycling - recycling grass clippings by leaving them on your lawn - does not cause thatch build up.
Clippings are very high in water content and decompose rapidly,
recycling nutrients back into your lawn...you'll have to fertilize
Earthworms and micro-organisms naturally reduce thatch. Earthworms
dethatch lawns by their activity - they are constantly mixing organic
matter on the surface and into the soil. Soil microbes use organic
matter for food...breaking it down into humus.
Conditions that reduce the activity of critters decomposing organic matter...
Avoid indiscriminate use of pesticides. Many insecticides harm earthworms and fungicides reduce soil microbe populations. Pesticides should only be used after you have identified the cause of the problem and have determined it is necessary.
Aerating with a core aerator promotes better air, water and nutrient movement into the soil. It also brings soil to the surface mixing into the thatch layer. This stimulates microbial activity speeding up thatch decomposition.
Top-dressing with a thin layer (1/8 to 1/4 inch) of compost adds organic matter full of microorganisms.
Have your soil tested every couple years. Follow the recommendations to correct soil pH.
If you have a serious thatch problem, thatch can be removed with a power rake or vertical mower. These machines have steel spring-like or knife-like tines that rotate perpendicular to the ground. After mechanical dethatching, the cause should be addressed or your problem will likely return.
Mechanical dethatching is hard on lawns. It tears out grass along with the thatch. Therefore...the best time to dethatch is when conditions favor rapid recovery. Fall or early spring for cool season grasses. Late spring (after green up) or early summer for warm season grasses.
Fall is the preferred time to dethatch because few weed seeds are sprouting. You can also follow up the process with overseeding and fertilizing to fill in thin areas.
causes much less damage to existing turf than power raking or
verticutting. Aerating at least once a year should keep thatch in