Agriculture Reference
In-Depth Information
Mulch
Thick, dense mulching in the garden with the right material provides a huge array of be-
nefits. You can certainly say goodbye to most of your weeds when you apply a thick mulch.
Not only does it smother them out both physically and sometimes biochemically by tying
up nutrients on the soil surface, it makes the ones that do find their way through so much
easier to pull, especially if you've been clever enough to hit the garden and the mulch with
some water. Note that it may be necessary to kill some tap-rooted or perennial weeds be-
fore placing the mulch on top of them.
When we mulch, we create homes for insects and other animals and provide them (and
microbes) with food. They take this food and turn it into available minerals and humus, in-
corporating it into the soil to create amazing soil structure. Then all of the other benefits of
good organic matter begin to accrue — increased CEC, water-holding capacity and fertility,
and decreased compaction.
The mulch itself serves to decrease the compaction caused by us walking on the soil and
from heavy rains, and can help to prevent erosion. It moderates the soil temperature, bene-
fiting everyone living there. Some studies have concluded that mulches and cover crops
make soil cold in the winter and increase frost damage, but these studies are using dead
soil, and this does not happen on real, organic soil that is actually kept warmer during the
winter due to the insulating capacity of the mulch and the activity of microbes and animals.
So mulch actually improves the biodiversity of your entire soil ecosystem by giving all
manner of critters a place to live, food to eat and water to drink.
Why not just use compost? A little bit of thought tells us why. It does a lot of things
right, but fails to stop the weeds. The same goes for manure. Manure can be a very useful
soil amendment, but it needs to be well composted and should really be mixed in a proper
compost pile. On its own, it isn't a valuable, balanced nutrient source, since the animal kept
most of the trace minerals for itself and gave up excess nitrogen and salts. Indeed, many
studies have shown that soils continually amended with the same manure will eventually
produce unhealthy plants. We can use compost and manure, but they don't make the best
mulch. We'll look at them in the next chapter.
Mulch is often applied two to three inches thick, and should be kept away from tree
trunks, which don't want to be covered in anything. If you want to promote fungi, such as
in a perennial or shrub garden or around trees, put the mulch on the surface. If you want to
promote bacteria, such as in an annual or vegetable garden, incorporate it lightly into the
top few inches of soil to give the bacteria better access. For bacteria, also consider chop-
ping or grinding up the mulch into smaller pieces, and make sure it's plenty wet, as bacteria
need moisture more than fungi.
