The Magic of Mulch
Mulch is incredibly useful any time of the year, but even more so now, as we head into summer.
What makes mulch so useful?
It retains moisture in the soil. It should always be laid down after rain/when the soil is damp. Have it at the ready so when the rain comes, wham, you can lock it in!
Vegetables, flowers, herbs, fruit trees and soil microorganisms all grow better in damp soil
Soil biodiversity increases:
Mulch feeds soil microorganisms- the woodier it is, the more the fungi like it and the greener it is, the more the bacteria like it.These microorganisms break the mulch down over time and make the nutrients available to plants. Mycorrhizal fungi love mulch too and plants benefit from their protection and the nutrients they scavenge. Worms and plant roots come up the surface to feed. Soil biodiversity increases.
Then there are all the soil insects and mites which chew and gnaw away
As mulch breaks down, it contributes valuable organic matter to the soil, so the soil is better able to breathe, and absorb/hold water
Mulch protects bare soil from being compacted/eroded by heavy rain or wind
It keeps the soil cooler in summer, protecting from intense sunlight, and insulates it from the cold in winter
Finally, mulch suppresses weeds.
It is super useful to use between rows of direct sown crops like carrots and beetroot and around the base of long term crops like peppers and eggplants, and for sheet mulching pumpkin and melon patches (see below) .
Note: There is a misconception that laying leafy or woody mulch directly on the soil robs soil nitrogen as the microorganisms that break the carbon rich mulch need nitrogen and get it from the soil. . This would definitely happen if the mulch were mixed into the soil, but the point of contact between soil and mulch is only very fine sliver and does not present a problem.
Some Pointers on How to lay Mulch
You can plant first and then lay mulch around and in between your seedlings, or you can lay mulch down and then clear the mulch away from the planting hole.
Avoid laying mulch right up to the plant stems or tree trunk where it can cause stem rot.
Avoid putting mulch down on dry soil. It can prevent short lived but precious showers actually getting into the soil.
Not too thin, not too thick!! Generally laying mulch about a finger deep is ideal- between 5 and 8 cm.
Mulch that is laid down in a very thin layer will simply encourage weeds to grow, not suppress them.
On the other hand, if you have sown a green manure, or some wild flowers, or even a direct sown crop of carrots or coriander, a thin layer of mulch will help them to germinate by keeping the soil surface evenly damp, without suppressing growth.
Mulch that is laid down very thickly going into winter can stop soil drying out which is not helpful if the soil is heavy and wet by nature, and can lead to anaerobic conditions.
What to use
Mulch can be graded from the quickest to the slowest to break down.
Grass clippings
These break down very fast and are light, so offer limited protection to the soil. If they are fresh, and you lay them too thickly, they can go anaerobic and smelly, forming a slimy mat over the soil, which isn't ideal! Dried out grass clippings last longer and tend not to mat in the way green clippings do. If you have nothing else, use grass clippings. Better is to mix them with coarser materials such as chip.
Note: Be careful of using kikuyu clippings, as unless completely dead, pieces can take root. If lawn clippings are full of weed seeds, they too will eventually grow.
Caution: Be careful of using other people’s lawn clippings, as they may have been sprayed with herbicides - some of these are very persistent and will in turn damage your plants. This is why many compost companies no longer take lawn clippings.
Seaweed
Seaweed, especially kelp, is very nutritious for the soil, being high in potassium and trace elements. Generally it is slow to break down and tends to dry out into hard strands. I like to place it under a layer of banna grass mulch so it stays moist and can release its nutrients.No need to rinse salt off it unless you are using big amounts.
Woody Mulch
Woody mulch especially benefits woody plants- fruit trees, natives, berry plants including blueberries and strawberries, as well as roses.
Wood chip of most kinds is good, but avoid macrocarpa.
Manuka should rot down for a year or so before using.
Bamboo mulch is excellent and breaks down over about 18 months-2 years. Great for paths, fruit trees and perennial herbs and flowers.
Banna Grass breaks down over 9-12 months depending how much rain there is, and is perfect for mulching pumpkins, melons and onions.
Avoid woody mulch that is very fine - for instance saw dust. It tends to compact and reduces air flow into the soil. Never use sawdust from treated wood.
Compost? Yes, but….!
Well made compost is precious- it takes a lot of effort, resources and time. I personally prefer not to mulch with well made compost, as the sunlight and air break down the organic matter by oxidation, and the microbes go dormant or die as they dry out and are exposed to intense UV light. Compost needs to be put IN the soil, for instance by adding to planting holes, double digging or simply forking it in. If you are lucky enough to have enough compost to layer over the soil, go ahead BUT then cover it with a layer of mulch, thereby protecting it from sunlight, keeping it damp, and allowing the microbes to do their thing.
Leaf Litter from the Bush? No…
This would be a case of “borrowing from Peter to pay Paul”… the bush will suffer. Leave bush litter where it belongs. Often litter will wash up on beaches and this is useful.
Sheet Mulching
This is very useful when planting out a small orchard area or a pumpkin or melon patch. It suppresses the weeds already growing (although kikuyu may still wheedle its way through) and creates a great environment for plant roots to establish. It's a bit like building a spread out compost heap, but it will never heat up.
Get all your materials together
Browns /high carbon
Cardboard with tape removed SOAKED
Wood/ bamboo chip
untreated sawdust
Dried grass clippings
hay/straw/rushes
greens/high nitrogen
Blood and bone
Animal manure
Grass clippings (fresh )
Have a hose on hand
Mow or weedeat the ground very close
Soak the soil
Spread a layer of manure/blood and bone on the wet soil
Place a thick layer (2-3 sheets) of wet cardboard over the manure, making sure to overlap well
Lay manure over the cardboard
Then alternate layers of brown and green mulch over the top.Water the layers if dry.
Finish off with a layer of weed seed free mulch
Planting into Sheet Mulch
If planting pumpkins or melons, clear some of the mulch out from the planting hole and add a good couple of handfuls of compost/soil/worm castings and plant into that
Les Blackwell’s Sugarcane Mulching System
Every autumn, Les sorts newspapers that he has gathered over the year into sets of three sheets. He cuts down the canes of his sugar cane hedge into similar lengths. On a still day, he lays the three sheets of newspaper over damp soil, and lays the sugarcane over the newspaper, and allows it all to rot down over winter, creating a weedfree area to plant in the spring!
Living Mulch
Another trick is to plant your vegetable garden so plants cover and therefore shade the soil. Fill in gaps between slower growing heavy feeders with fast growing crops like pak choy, lettuce, Hakurei turnips and spinach or even alyssum and other insectary flowering plants. Cabbages fit very nicely on the edges of the beds between round, large zucchini plants.
