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Thatch in lawns

Thatch is a layer of organic matter which develops between the soil and green vegetation. It consists of living, dying and dead material in various states of decomposition. Thatch is the home to a multitude of microorganisms which play an important role in keeping the home lawn healthy.

During the growing season grass goes through a constant cycle of growth and decay. Grass clippings and dead and dying roots and shoots collect on the soil surface to be broken down by soil microorganisms and earthworms. This decomposition provides a constant supply of organic matter and plant nutrients which keep the grass healthy. The soil microorganisms also help to break down soil nutrients to make them available for plants. Diseases may be kept away by these beneficial soil inhabitants.

Thatch is a necessary part of the home lawn and should measure in the range of 1/4 inch to 3/4 inch. It provides a cushion for the grass roots so that the lawn can withstand being walked upon. In sports fields, the thatch layer makes the playing surface safer for the players. Accumulation of thatch above one inch, however, can lead to several problems.

A thick layer of thatch will inhibit the movement of water through to the root zone. Like a sponge, the thatch soaks up water and creates drought-like conditions for the grass. Roots will tend to grow in the thatch layer to seek out the moisture rather than growing deep into the soil. This creates a weak lawn which is very susceptible to drought or injury from wear.

Too much thatch will also interfere with fertilizer and pesticide uptake since they get tied up in the thatch layer and may never reach the root zone. Concentrated chemicals can harm the soil microorganisms. As well, insecticides caught in the thatch won't reach their target: insects which feed on grass roots are active just below the thatch layer. This is why watering the lawn after an insecticide application is recommended.

Diseases will tend to invade thatchy lawns because the naturally occurring soil microorganisms are not thriving and unable to fend off invaders.

There are many factors that can contribute to an excess accumulation of thatch. Essentially, the problem is too low a rate of decomposition of the dead and dying plant material.

One cause is the absence of earthworms and a decline in the population and activity of the soil microorganisms. It is important to maintain a happy existence for the soil inhabitants so that they work in our favour.

Thatch will also tend to develop when lawns are grown on poorly drained or compacted soils. These conditions prevent oxygen from reaching the soil microorganisms and they suffocate.

Finally, high nitrogen fertility may produce grass clippings more rapidly than they can be decomposed, creating a build up of too much organic matter. Or, over-watering, especially with high nitrogen fertility, will both drown the soil microorganisms and encourage too much top growth.

A thatchy lawn is an indicator that there is a problem with the growing environment. If over fertilizing and over watering is the cause then this is easily remedied by reducing this activity. If drainage and compaction are the problem then a regular de-thatching program will be necessary.

Thatch in home lawns is best reduced by physical removal. In the spring, a vigorous raking will help to remove excessive organic material. De-thatching or vertical mowing can be done with specialized equipment. Vertical mowers literally chop the leaf blades in a vertical position and drag up a large amount of plant parts. The organic matter which is brought up to the surface is removed by raking and followed by a regular mowing. The lawn will be a little bruised but be better for it! Vertical mowing should only be done in the spring and fall when the grass is actively growing so that it has a chance to recover.

Liming or "sweetening" the soil generally helps the soil microorganisms by keeping the pH at the level which most suits them. Apply Dolomitic Limestone in the spring and fall at 5 lb/1000 sq ft.

Daisy Moore, 1998.



Other spring garden tips:

(click on the tip you want to read)


Designing Gardens

Fertilizing the Garden
Ready for Spring
Starting Seeds Indoors
Pruning Trees and Shrubs
Dormant Spraying
Planning the Vegetable Garden
Planting Early Vegetables
Early Season Care of Perennial Beds
Plants for an Early Spring Show
Cut Flowers for the Home Garden
Growing the Perfect Potato
Lawn Care in Early Spring.....GRUB DAMAGE!
Spring Lawn Care
The Garden in May
Gardening with Native Plants
Sources of Native Plants
Shade Gardening
Planting Gladiolus and Other Summer Flowering Bulbs
Weed Control
Thatch in Lawns
Weeds or Wildflowers
Improving Your Soil
Marvellous Mulch
Selecting and Planting Shrubs
Planting Trees and Shrubs
Window Box Gardening
Growing Tomatoes
Fertilizing the Vegetable Garden



Home  |  Garden designs  |  Naturalized gardening  |  Help with your garden  |  Garden Tips Spring  Summer  Fall  | Contact Daisy


Daisy Moore 2005