Leaves
are the cheapest and most effective mulch for weed control, when enough of them
are used. This natural gardener has been
using them professionally on clients’ yards for 13 years. All other mulches are seed beds by
comparison. Leaves feed the soil and
thus the plants; soften it for easy weeding; and can stop sprouting of most
small seeds, just by keeping the sun off them.
As long as leaves stick around, they stop germination of seeds that land
on top of them, because the top few layers dry out quickly and don’t allow
seeds on top to sprout.
One
can smother nearly any annual weed, and many small perennials, with enough
leaves. But to be efficient with a
client’s money, a professional gardener must figure out the least that it takes
to do the job effectively when one has to bring them in from other places.
There
is no need to shred leaves to use them for mulch in most situations. Whole leaves are better for blocking weeds,
but leaves can be mowed into a lawn, and shredded leaves will stay in place
better where the wind would otherwise blow them around.
Only
very large trees drop enough leaves beneath them to stop larger annual grass
seeds like cheat and foxtails, but taking them from pavements, roofs, lawns,
paths, and neighbors with too many and spreading them more thickly in beds and
borders can smother grass seeds and young weeds while encouraging larger
established perennials.
There
are three basic classes of leaves as mulch: soft leaves; tough broad leaves;
and tough conifers. Black walnut is a
soft leaf in a class of its own, containing a pre-emergent herbicide, juglone,
that stops smaller seeds all summer, though their leaves are eaten before
winter is over.
Red maple leaves, blown onto a weed field from fine bark. Not thick, but still smothering groundsel seeds.
Although
soft leaves may be eaten by soil life before summer is over, and sometimes
before fall or winter is over, they can have great smothering ability until
they are eaten. Many tend to lie flat over
seedy soil and stop spring weeds like groundsel and bitter cress, even without
extra leaves piled on. Piling them 6
inches or more deep will preserve the top layers of leaves over the entire
season, as they quickly dry out on top while the worms happily eat the damp
bottom leaves. But that’s a lot of
leaves unless one wants to grow vegetables.
In that case, a foot is even better.
Oak leaf mulch under a large oak
Hard
leaves, like oak and sweet gum, stick around the entire season, but tend to be
stiff and fluffy, and thus allow seeds to grow through them to the light. Again, it usually takes more than naturally
falls under the tree to stop many weeds, particularly annual grasses with larger
seeds. Merely covering the ground is
insufficient, especially with weeds already growing.
Pine needles naturally fallen beneath the tree.
Pine
and true cedar needles are good for covering other leaves to hold them in place
and give a consistent, quiet look to one’s mulch. They are also good for covering compost
spread on top of soil or leaves to aid seed germination, when spread just thick
enough to hide the compost seed bed.
Piled over an inch deep, they stop germination as well as other leaves,
as they pack down fairly tight. They can
be used for path cover, but pine are rather slick and not suitable for slopes. Flat or non-needle conifer leaves, like fir,
incense cedar, redwood, and sequoia, are soft and decompose as fast as other
soft leaves.
Pine needles spread as mulch. They are much used in the South, going by HGTV.
Six inches to a foot of leaves can
grow big food plants. But piling one
kind of leaf too deep can occasionally result in slow decomposition and slow growth
of plants. A mixture of several kinds of
leaves has more variety for the soil life to eat, more nutrition, and allows
water to move down through the stack more efficiently. It is important to spread them in layers and
keep the surface relatively flat, so the water doesn’t just run off the top or
around bundles of leaves.
One can grow garden seeds in a thick
bed of leaves if one spreads an inch of compost on top of the leaves and plants
into and on it. This even works on top
of black walnut leaves and soil, keeping the seeds separated from the juglone
long enough to sprout. Compost also
helps decompose leaves more quickly for early spring growth. But it is not necessary for planting large
seeds, like beans, corn, and squash, into the leaves. Poke them in to where you can feel moisture
for them to sprout in.
But for non-food-growing areas, a
mulch of leaves with several thin layers, each just thick enough to hide what
is beneath, can provide maximum weed control with minimal leaves. Use soft leaves on the bottom to smother and
physically block seeds and small plants from growing. Hard broad leaves can be spread on top of
those to keep the sun off the soil all summer.
Pine needles go on top to keep the leaves in place and give a
consistent, calming look to the landscape.
Leaves
work well for mulching beds and borders, but weeds in paths have to be
controlled, too. Just about any material
one puts on a path will sooner or later become a seedbed for whatever lands on
it, except for pavement, and even there, they will grow in the cracks and
holes. Organic path mulches must be
renewed every year or so. Gravel is a
headache once it fills with seeds and dirt.
4 x 8 sand, surrounding beds.
But
a half-inch of 4 x 8 sand, which is river sand screened ¼-1/8 inch, can let you
defeat the weeds by bringing them up right away, so you can slide a scuffle
hoe, AKA hula hoe, underneath their crowns and pull or cut them off their
roots. Rake out the weeds, and your path
is cleared without bending.
The
key to how 4 x 8 sand works is that, when particles of different sizes are
disturbed, the smaller sift to the bottom and the larger end up on top. Dirt and small seeds on the path are sent by
hoeing and raking to the bottom, and rocks and sticks larger than the sand
float to the top where they can be raked out or picked up and thrown in the
bed. Quarter-inch rocks dominate the
top, and don’t stick to shoes. When
seeds sprout, their crowns form at the top of the sand, so they are easily cut off
their roots. Very young plants whose
crowns are cut off their roots are killed, as they have no food in their roots.
Gardening
is easy, if you do it naturally.
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