Mulch – The Good, Bad, and Ugly

Mulch has been used in many cultures for thousands of years. American Indians used both living mulch (pumpkin with corn and tomato) and sophisticated composting processes such as their famous biochar.

Over 26 years we finally eradicated invasive Kikuyu grass from our food forest without the use of any poisons or plastic. We used the permaculture strategies of starting small and reading the landscape. We targeted our efforts by putting spot mulch around trees. Then the canopy helped shade out the grasses. We also adopted a philosophy of least resistance. We asked “what does this weed want?” and simply set out to not provide what it wanted. The Kikuyu wants bright light, mowing or grazing, water, and room to move. We soon discovered that it weakened when it was not mowed, exhausted itself when allowed to send long runners, and died back in the shade.

Long term, mulch makes fantastic new soil and reduces weed infestation. Mulch is always useful to reduce evaporation, protect the soil and worms from erosion, and increase your store of organic material.

We use paper waste underneath mounds of grass clippings

Mulch Mistakes

Here are a few tips and how to avoid unplanned effects.

Start deep, then spread it out

Mulching too thinly simply encourages existing weeds and their seeds to thrive. So, keep your mulch deep and thick. These piles can also serve as temporary swales to direct water flow.

Fresh grass clippings, weeds or prunings often contain seeds or tubers that resprout where you don’t want them.

However, the problem is also the solution. Mounds of fresh clippings can generate heat and burn the plants below. But this can be handy burn out a weedy area containing seeds. Contain the mulching material by keeping it in a heap until it has stopped burning (the burning kills weed seed within the heap too) then apply the mulch when it has cooled and all fresh organics have turned into brown, aged organic waste.

A Balancing Act

Mulching material that is highly acidic, or all one type of material such as citrus peel can attract bugs, but they are doing the job of breaking it down for you. Keep this type of mulch away from delicate plants until it breaks down. Best of all, mix it with other materials to correct the pH imbalance and speed up the compost process.

Rats will thrive with abundant fresh food waste. Keep their favorite foods in metal bins until it decomposes, then apply the composted food scraps to the garden.

Another hazard from pure organic material that has not yet decomposed is nitrogen draw-down. This is noticeable when the leaves of plants near the mulch begin to turn yellow. To reduce this risk to young plants, include a layer of composted or aged urine or manure underneath the top layer of ‘green’ material. Essentially, the site will benefit from a balance of green materials (fresh organics) and brown (aged materials such as paper or dried wood).

Allelopathic chemicals (such as Eucalyptus) – this will not be kind to any tender, unaccustomed plants. Basically, be aware that non-natives may not like native mulches.

Why Your Tree is Scared of Mulch

Mulch that sits close to the trunks of your trees can slowly kill them. The tree trunks develop collar rot and rots away. In fact, the living part of a tree is the bark. The bark is vital yet vulnerable. Unlike humans, the skin of a tree is main artery system. Food sugars go up and growth hormones and messages travel down to the roots. This all happens through the thin skin of a tree. Keep wet or hot mulch away from the skin of a tree.

Seedpod of Illawarra Flame sprouted naturally in deep composted mulch

When Not to Mulch

Mulch blocks weeds but it also inhibits the germination of good seeds from last season. If you find that you tend to get lots of seedlings in the paths of your gardens and not in the beds that is probably because the mulching material has stopped seedlings being able to sprout in the beds. Choose to mulch at the right time, after seed germination if you wish to find new plants each season.

Some materials do not decompose quickly (eg. hair, old wool, re-used cotton from an old futon) so they are good long term protection or other tasks such a filtration. The ideal mulch is living mulch which replenishes itself year after year. Living mulch can be edible such as sweet potato (kumura) or better still, find an indigenous ground cover to add to your food forest.

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living mulch edible
sweet potato – excellent living mulch with edible leaves and tubers