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The Magic of Mulch.

Mulching is the placing of organic materials like plant matter or inorganic materials such as rocks or plastic sheeting on top of the soil around plants. Mulching is one of the most valuable activities you can do in the garden for many reasons. Mulch performs a multitude of tasks depending on the type of mulch you use.

Benefits of Mulch.

The benefits of mulch are many. Organic mulches will help build soil nutrients as well as suppress weed growth and retain water in the soil. Mulches can also help protect plants from frost and reduce soil erosion.It is also useful for controlling soil temperature to a degree.

This quality can be useful in a couple of different ways: if you want to delay blossoming of fruit trees, for example, so that a late frost won't destroy early blooms thus fruit, a thick mulch of something like straw around the roots of the tree will keep the soil temperature down thereby delaying the blossoming by a week or so avoiding the frost. Conversely, you can warm the soil with a dark coloured or stone mulch. Stones will absorb the heat through the day and reradiate it back at night. This is useful for protecting frost tender plants by reducing the likelihood of the soil freezing which is what causes the damage.

The most common reasons people mulch is for weed suppression and moisture retention. A thick layer of mulch will severely inhibit a lot of annual weeds from growing. It needs to be at least 10cm (4in) thick to work well. Those weeds which do make it to the surface are often weak and easily pulled. When dealing with more persistant weeds like bulbs and runner grasses the mulch used needs to be hardier and more enduring or impervious. This can lead to other problems however such as lack of water penetration. Over-lapped layers of newspaper with something else on top to stop it blowing around makes a good weed proof barrier but can become impervious if allowed to dry out. Soak the newspaper thoroughly before laying it down. Eventually the paper will rot and disappear into the soil by which time the primary planting should be well enough established.

The moisture retention qualities of mulch are invaluable particularly in dry or arid environments. Keeping the ground covered will significantly reduce the amount of evaporation. It means less water is needed to maintain healthy plants. Also plants will be less stressed if there is a balanced continuum in soil moisture content.

Mulch protects soil from erosion by both wind & water. The layer of material will stop the direct action of rain drops splashing on the soil and displacing it so that it washes away when there is enough rain to actually flow. Likewise it prevents the soil being picked up by wind and carried away. Mulch helps the soil to more readily absorb water, as does building up the organic content of the soil in the first place.

Another benefit of mulch, particularly of an organic nature is that it attracts earthworms. Soil which is prolific with earthworms is a sign of the high fertility. Worms are capable of changing an enormous volume of organic matter into castings (worm poo) which is the nearest substance to humous. Humous is a colloidal substance in soil from which plants get nutrients. The higher the percentage of humous in the soil the more fertile it is and the better plants will grow. So having lots of worms in your soil is fabulous. It will also help with the aeration and structure of soil. I could go on about the value of worms but will save it for another article.

Types of mulch.

Mulch falls into two broad categories; organic & inorganic. In this instance the word organic is not referring to an absence of chemicals but to a group of materials of a natural origin which will eventually break down into the soil. Inorganic mulches will not decompose to become part of the soil.

The general rule is that any mulch is better than no mulch.

Examples of organic mulches:

  • lawn clippings— best to allow lawn clippings to decompose a little prior to using. Also it is better combined with another material like leaves as the even sized particles of grass can form a water resistant mat on top.
  • leaves
  • comfrey— this herb with large leaves which die back each year is also good for mulching with because of the high nutrient value of the leaves. Comfrey has deep roots which will 'mine' nutrients further down than many plants go making it available to the shallower rooted plants nearby and whne used as mulch.
  • greengrocer wastes
  • sawdust— use in combination with a high nitrogen source like fowl manure or blood & bone or the sawdust is likely to 'borrow' nitrogen from the plants as it decomposes. The plants will become stunted & sickly.
  • seaweed
  • shredded bark
  • pine needles— is of an acidic nature so good around acid loving plants like strawberries.
  • shredded weeds— be careful not to include any weeds or grasses which are likely to grow from small pieces of roots.
  • soaked weeds— this is a good way of dealing with noxious/runner weeds prior to mulching with it.
  • wilted weeds— if it hasn't gone to seed and doesn't grow by root division weeds can be left to wilt in the sun then spread around other plants.
  • mushroom compost
  • manures— especially grazing animal's manures and old manure. Take care when using fresh as the excessive nitrogen can burn plants. Probably best used in combination with other materials.
  • grow-your-own mulch— choose a selection of ornamental plants or 'green manure' crops which grow prolifically in your area. These can either be cut back regularly or prepared and used in any of the same ways described above for weeds.
  • shredded paper— this has negligible nutritive value even when fully decomposed but is still organic in that it came from nature originally and will decompose eventually.
  • newspaper— It can make an excellent weed barrier especially under something like sawdust or bark chips on a pathway. Beware of coloured inks which may be toxic or contain heavy metals.
  • plant prunings & thinnings— use the bits trimmed off plants or the excesses thinned from a clump as mulch. It's best to use it around a plant not of the same type so as to reduce the chances of disease spreading. Avoid using diseased material without first sterilising using some method. Aromatic prunings and leaves can be effective pest repellents in some cases.
  • living mulch— whilst not truly a mulch in a sense, the concept is the same. With living mulch you grow low growing prostate plants beneath taller species as a means to keep the soil covered to reduce evaporation & erosion. Some species of plants may also be well managed with regular trimming or mowing. Others may also release nitrogen when pruned making it available to the nearby plants in this way complimenting the association. This form of mulch is a particularly useful practise in arid regions.

Examples of inorganic mulches:

  • stones— whilst being from nature, stones will not perceivable decompose. Rocks such as limestone may leach a little with the addition of water causing the soil to become a bit alkaline. Be aware of this around acid loving plants like strawberries, camelias etc.
  • woven plastic matting— the woven plastic weed mat is good in that it allows water to penetrate. On the down side it is a comparatively expensive option and detracts from the natural look of a garden unless covered by something else. The same goes for plastic sheeting.
  • plastic sheeting— good for weed control but doesn't allow water penetration or air circulation within the soil.
  • old carpet— this may breakdown over time if it is made of a natural fibre. Carpet is good for weed suppression and under a more attractive surface mulch on paths etc. May also hinder absorption of water.

Techniques of Mulching.

As many mulch materials are higher in carbon content than nitrogen until they have decomposed it is best to place fresh materials over older mulch. This is because the material will use nitrogen to decompose and will take it from your plants until broken down when it becomes available to the growing plants again. Alternately, feed the mulch with some high nitrogen organic additives like blood & bone, diluted urine, liquid manure (compost water), seaweed or fish fertiliser, fowl manure etc.

Other valuable organic nutrient sources may include: dolomite or lime, wood ash and rock minerals like rock phosphate. These are best put onto the soil first before adding other layers of mulch. Spread these which a light hand as too much may burn off seedlings or kill valuable *micro organisms within the soil.

Avoid placing mulch right next to the trunks or stems of plants as it may cause coolar rot in some instances. Sometimes it is easiest to lay down the layers of mulch on the prepared garden area then pull back small pockets into which you plant the intended seedling.

Build upon layers of mulch as materials become available to you. Ultimately all soil is best protected by mulching. It is a practise of all good organic gardeners for all of the benefits it gives. The magic of mulch lies with you, the magician.



*To gain a better understanding of the importance of bacteria in soil and our bodies read the article

'Bacteria to the Rescue'.





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Susan Greentree

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