The prime reason for mulching our garden beds is for water retention and to keep the soil and roots relatively cool during hot weather. Ideally each plant should have a minimum of a bucket full of water a fortnight. Then to keep the water contained, you need to mulch.
Many gardens use inorganic mulches such as stones, pebbles or gravel to a depth of 30 cms. Water can penetrate these mulches and be retained below the layer of stones, but hard inorganic mulches add nothing to the soil. Other inorganic mulches such as weed control matting or shadecloth can be used but these encourage shallow root systems, stifle oxygen intake and again, add nothing to the soil.
It is better, in my opinion, to use an organic mulch, which will help in keeping the roots cool in summer, and in breaking down, will enrich and improve the soil structure. The addition of organic material can greatly improve water retention and fluff up the soil. Working these products into the soil can add more texture to keep the soil loose allowing roots to grow more effectively.
However, it is important to understand the process of breaking down and what this does to the soil. Let us look at the more common mulches available to us.
Wood chips should never be put on when fresh and green. The heat generated in ageing the chips will burn the roots and canes of the rose bushes. The breaking down process robs the soil of nitrogen, which must be replaced. Pine bark is acidic and will alter the Ph of the soil as well as robbing the soil of nitrogen. If the shredding process is very fine, the pine bark will act in reverse of what we want, by clumping and forming a solid barrier which the water cannot penetrate.
Grass clippings to a depth of about 3 cms will work except that the breaking down process will lower the Ph. Too heavy a coating will generate heat and burn the roots and canes. It can also tend to go mushy and useless. It will blow away in the wind and unless composted, will cause a real weed infestation. Similarly, stable manure will cause the same problems as grass cuttings. Note Avoid Pony Club manure – you don’t know what they have been fed on.
Pea-straw and Lucerne hay are popular mulches, but both will blow away in high winds, both run the risk of weed infestation – Peas in the case of pea-straw; Lucerne in the case of its hay. If you have a tree which sheds its autumn leaves, pile them up, run them over with your mower, compost them and you have one of the best mulches there are.
Grass clippings, stable manure, pea-straw, Lucerne hay and autumn leaves are good soil conditioners as well as mulch, if gently dug in and if you are prepared to fight any possible weeds.
Sugar cane mulch is available commercially, and I suspect it will have the same effect as Lucerne hay. I have not used mushroom compost, but suspect that, if you can afford it, it would be very valuable as it has already been composted and would add fluffiness and enrichment to the soil.
Our good friends at Neutrog, have introduced a “biologically activated, nutrient rich, weed free, absorbent, super mulch” which they have named WHOFLUNGDUNG. I believe it has a pungent aroma which may deter some people from using it, but it sounds like a winner.
Wal J 3 Oct 2018
