Question
Do you have any clue why grass builds up thatch? I am new to this and we would like to understand what is going on here with the grass. The lawn guy says we have a thatch problem and he wants to solve it at the cost of insane amounts of money. Gas is too expensive right now, heat is expensive, a/c is expensive, I would like to know if this is a real problem or if we can just leave well enough alone. Thatch advice?

Answer
Thatch is a layer of intermingled roots, dead stems and crowns of the grass. Thatch is mainly created by aggressively spreading grasses, such as bermuda, st. augustine or zoysia. It is seldom found in cool season grass, although it can.

If you dig a core of soil 4-6" deep and look at it very carefully. You will be able to see the soil and then a brown (almost soil color) layer of "felt" like material (actually decomposing stems, roots and crowns) between the green grass and the soil. This layer is not a problem as long as it is 1/4" or lower. If it is more than 1/2" it can prevent water and nutrients from reaching the grass roots. If it is more than 1/2" will should be clearly visible and it may be spongly when you try to pull it apart.

Here are a few pictures of (extreme) examples of thatch:

http://www.ppdl.purdue.edu/ppdl/images/K_blue_thatch.jpeg

http://www.oldhouseweb.com/gardening/garden/visuals/thatch01.jpg

http://versicolor.ca/lawns/img/ThatchDPlg.jpg

http://www.nutrite.com/images/FeutreEpais.gif


You can deal with thatch in one of two ways:

- core aerting. Core aerator machines pull cores of soils (look like small cigarettes) and deposit them on top of the lawn to decompose. A machine (like an oversize mower) can be rented at equipment rental stores for $40-50 per day and it can be done in 1/2 day for most home lawns. It is operated like a mower. It will pull 20-40 plugs per sq foot. You need a pickup, suv or van and two people to transport the machine from the rental store to your place.

- de-thatchers (vertical mowers) are machines which rip out the thatch. Two types are commen: 1 type which has metal arms which moves around and rip up the thatch (destructive). Another type has knives (also called vertical cutters or vertical mowers) and they slice through the thatch. You can set the dept of slicing on the machine. This machine can also be rented at equipment rental stores and you need two people plus a large suv/van to transport. Same rental costs as the core aertor.

If the thatch is less than 1" in dept (which would be A LOT), I recommend CORE AERATING. This process is highly beneficial to the lawn as it elivates compaction, allows oxygen, water and nutrients to reach the root zone. The aerator punches through the thatch.

If the thatch is more than 1" deep, the use a vertical cutter (with knives that slices.. not the arms) and run over the lawn in several directions. Then also consider following up with core aertors.

Before you rent, check the thatch dept yourself by pulling cores of soil (with a shovel or coring tool) and look at the soil profile carefully. Check it against the pictures above.

Good luck.