Mulch is matter that is placed on top of the ground as a covering (NOT tilled into the ground). All bare soil should have a cover of mulch to protect it, including ground underneath shrubbery and trees.

Although some people like to mulch for the improved appearance, the real purpose of mulch is to protect the health of the soil. Mulch lessens the effect of extreme temperatures. During summer months bare soil may reach 120 degrees F, but if that same soil were mulched, it may reach only 85 degrees F. In addition, mulch increases moisture retention, prevents top soil from washing away, and reduces soil compaction. One of the great benefits of mulch is that it shades out weeds. By covering the ground, weeds cannot recieve enough light to grow. The few that do survive are so weak, they can be easily removed.

Though not very attractive, the hay bricks I use as mulch around my compost pile (picture at right) are utilitarian in nature. Because I'm always moving my piles, the area around them is bare soil. The surface of my clay soil gets crusty as it dries out in the hot Texas sun. Then when I water the piles, I have standing water for a while which eventually soaks in and leaves mud. HAY MULCH solves the problem. It keeps the soil from getting dry and crusting so that water is absorbed into the soil instead of sitting on top. I am protected from the mud by 3 inches of hay as I walk around the piles. More importantly, my dog Alex is protected from mud as he walks around the piles!

Water area to be mulched. Before you lay down mulch, first cover the ground with sheets of wet newspaper or cardboard. This will make it even harder for weeds to grow.

Then, spread 2 to 4 inches of mulch materials on top. Do not till into the soil. The depth of mulch to apply depends on the material. If you are using sawdust, a very thin layer -- maybe only one inch -- is best because this material is so fine, air and water may not get through a thick layer. On the other hand, a coarse material such as hardwood bark or hay may be laid 4 inches thick.

Be careful not to lay mulch so that it is touching plants. Keep it 2 to 3 inches away from plant stems. Try not to lay it so thick that plant leaves are resting on it.

I used leaves to mulch around a young tree (photo at left). To protect the tree, I cut the bottom from the plastic nursery pot and put it around the tree as a collar. Then mulched around it with leaves. For heavier mulches and more established plants, a collar is not needed. Just start mulching 2 to 3 inches away from the base of the plant.

You can water plants right through the mulch. You can also put compost on top of the mulch and water it down through the mulch to the soil if you use coarse mulch materials. There is no need to remove mulch to apply compost. Organic mulch materials decompose over time, so mulch should be replenished as needed to maintain the appropriate thickness. Add the required amount of new mulch materials right on top of the old. For instance, if your 4" mulch from last year has decomposed to the point where there is only 2" of mulch left, add another 2" of mulch on top of the old.

In addition to partially completed compost, there are many other materials which may be used as mulch: pine needles, various types of wood bark or chips, pecan or peanut shells, shredded leaves, hay or straw, pecan or walnut shells, crushed rock. Use your imagination and experiment with new materials. It's best to use organic materials. Look for materials that won't mat easily and that won't blow away.

The Debate
There are some claims that partially-decompost compost and other mulch materials will rob soil of nitrogen as it completes composting. Most experts agree that nitrogen will be stolen for composting if the materials are TILLED INTO THE GROUND. But as long as the partially decomposed matter stays on top of the soil, there is no damaging nitrogen draft. That is why we recommend not tilling mulch materials into the ground. There may be some nitrogen drainage on the very surface of the soil, but not in the root zone. I often lay one inch of compost on top of the soil before I mulch. That way, even roots near the soil surface won't be effected. I have had no negative effects from mulch and I have been mulching for years and using as many different materials as I can find.

The forest floor, from the bottom layer up, consists of soil, finished compost, partially finished compost, barely-started compost, and fresh organic materials. If it is OK for nature, it is OK for me.

Note added 2010:
Check out the Mulching article I wrote for CompostMania's LEARN section.

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  1. Soil Incorporation
  2. In-Soil Ingestion or Digestion
  3. Trench Composting
  4. ** Mulching **
  5. Composting Toilets
  6. Compost Tea

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