One big advantage of organic mulches such as 'Strulch', lawn clippings, and bark, over artificial fabric, is that they improve soil texture and add nutrients. But that's not all. Here you will find how to use these materials and how they work. I reveal possible sources of supply, from homemade organic matter,
* Nature's own blanket to keep the earth open,
* Types of organic matter for mulching,
* Choice of plants & how to mulch them.
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If you're not diligent about replenishing bark mulch, it can start to look messy and start letting weeds through after just one season. These thick mulch mats are made of tightly woven coconut fibers
to products from forestry and agriculture.
Mulch has many uses in organic gardening.
Use organic mulch around your fruit bushes to retain moisture so fruit can gradually swell.
Under strawberries and around marrows, squashes and cucumbers it is used to support and protect fruit from damage.
For a sunny spot fragrant mulches are a delight while they keep your soil cool and moist.
A richly coloured mulch can set your flowers off and reduce weeds.
Use around climbers to maintain cool roots, and use it to protect bare soil.
The best Organic Mulch available to U.K. gardeners is Strulch.
You get 95% weed reduction and this stuff lasts much longer.
Click here to find Strulch.
How Organic Mulching Works
SOIL CONDITIONING AND FEEDING
The soil improvement from organic mulch is so amazing it has to be seen to be believed. (Images of fine soil don't do justice as photo resolution limits quality.)
A layer of leaves left over winter has by March turned into:
- a light crumbly layer of worm casts,
- dark moist organic matter and minerals mixed and bound into light crumbs,
- soil permeated with burrows for drainage and aeration,
- soil fed the ideal supplement to make an excellent seed bed.
‘No dig’ gardeners continually mulch their plots. The earthworms drag the organic mulch down and enrich the soil with humus. The improved aeration and drainage saves hard spade and fork work.
Organic mulch slowly adds nutrients to the soil as it breaks down. Mulch is a surface covering, but some gardeners like to work it into the soil. This can leave the soil temporarily depleted in nitrogen. It's best to leave organic mulch on the surface. see below
PROTECTS SOIL STRUCTURE AND REDUCES EROSION
Some soil types are especially vulnerable to structural break down by heavy rains. This can be due to the physical pounding of rain or calcium leaching. Weakly bound sandy soils are especially vulnerable.
Erosion is also a problem wherever surface water collects and runs off. These problems are more or less solved by adding a protective layer of mulch before winter.
MAINTAINS WINTER WARMTH - SUMMER COOL
Mulch can behave as a heat insulator and keep warmth in the soil over winter. This can prevent the soil beneath from freezing and protect delicate perennials. It also gives higher starting temperatures for earlier spring growth. Beware however; reducing heat transfer from soil to the surface may induce air frosts. see below.
Plants gain most benefit from warm soils in spring when seeds germinate and new roots grow out. But in summer there’s no gain in being warmer. Indeed heat stress can be damaging. Vines for example prefer to have cool roots.
Fortunately the insulating properties of organic mulch make the soil beneath feel a few degrees cooler in summer.
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PROTECTS AGAINST SUMMER DROUGHT - IMPROVES DRAINAGE
Cooler soil means less evaporation and most organic mulches will hold some water too. So the soil underneath is kept moist. This is ideal for surface rooting plants and fruit.
Importantly your mulched plants will have better drought protection to reduce stress during hot summer days and that benefits flowers and vegetables too.
As mentioned above the increase in earthworm activity and burrows helps to improve drainage and reduce waterlogging.
Like most mulches, organic mulch will exclude light and therefore prevent most annual weeds. Perennial weeds are mostly unhindered and should be removed first.
Take care:- some organic mulches e.g. hay, will contain weed seeds. Deep organic mulches e.g. wood chip over 5cm deep, may allow weed seeds to germinate within the mulch. If you're laying it over a geotextile base and this occurs, weed roots may tear the fabric.
Other mulches like lawn cuttings don’t seem to support germination or tender young growth, at least not when they are raw.
Think of the fall in woodlands - dead leaves decay, release plant nutrients and form black humus. This is ideal material to hold water and nutrients, and to make fertile soil.
Properties Of Good Organic Mulch
- Doesn't get water saturated,
- Drains freely,
- Permits good aeration,
- Free from contamination by weed seeds or fungal pathogens,
- Easy to make, or obtainable at a reasonable price,
- Nitrogen content not too low relative to carbon content,
- Easy to apply.
See table right >> for links straight to information on specific mulches which are described further down the page.
The above section has already explained several problems that can arise when organic material is layed on the soil surface.
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Thick layers of matted organic matter can use up oxygen and prevent its diffusion into the soil. Keep layers of grass cuttings to no more than 1 inch,
- Keep damp decaying mulch away from direct contact with plants. It could cause rot,
- Some organic matter breaks down to cause an acidic reaction in the soil; e.g. pine needles, some wood chip mulches. Don't use these around lime loving plants,
- The reduction of heat transfer from soil to air due to an insulating mulch could cause air frost. This effects exposed branches, dormant buds, or leaves. A good soaking before cold weather could alleviate this,
Many organic mulches have relatively high carbon content. This means that soil micro-organisms will take nitrogen from the soil to balance their ration. This causes temporary soil nitrogen depletion.
The solution is to leave organic mulch on the surface where it is intended to be.
Alternatively add nitrogen to the mulch. Comfrey leaves, comfrey tea, worm compost tea, garden compost tea, diluted urine, will all help to redress the balance. Also fish meal, fish emulsion, seaweed extract, plus the 3 fertilizer teas, might be sprayed over any plants likely to be effected.
When To Apply Organic Mulch
Apply mulch in autumn.
Remove mulch in spring for sowing or planting.
Once plants are established replace the mulch for the summer.
Organic mulch needs topping up because it works into the soil as it decomposes.
Types of Organic Mulch
Simply the very best organic mulch available in U.K. It is made of mineralised straw and lasts about 3 times longer than ordinary straw. It is very light to carry but clingy enough to stay put on the ground. The bulk is airy which prevents weeds seeds growing, but it keeps soil beneath moist. You get 95% weed reduction from a 1 inch layer. It lasts 3 times longer than straw.
I've laid it on my greenhouse beds and planted strawberries. It will protect the fruit, and slugs will find it uncomfortable to cross.
price Strulch on this link - U.K.
One of the most valuable of all organic mulches and often used as a base for seed compost. Its scarcity is a problem for me, so I’ll reserve its use to spread on a few special perennials. After spreading it further in my flower bed, my gooseberries may get a share.
Some gardeners take extra time to work it into the top inch or so of soil; something to consider before sowing vegetables e.g. beans. Don't forget to add shredded comfrey leaves to increase nitrogen content - check here.
Leaf mold can be homemade.
Make leaf mold by gathering fall leaves into polythene bags. Yellowed tree leaves are loaded with calcium but may be short on nitrogen. This is solved by adding alternate layers of wilted comfrey leaves. Moisten the bags, close, allow air in by perforating, and leave to rot. Leaf mold is available after 12 to 18 months.
You can speed up the process by fine shredding. Resistant leathery leaves might then be used to make organic mulch - leaf mold and compost. Tools for dealing with leaves in the U.S.A. Take care with poisonous laurel leaves.
Lawn Sweeper - U.K.
Compare the ALKO Blow Vacuum - U.K.
with the selection of Blow Vac's on this link - U.K.
These have become popular in U.S.A. and the South East is the main production centre for long leaf pine needles. These are easy to harvest and bale and easier for the gardener to handle. They are much less likely to be kicked and spread around as happens with like pine nuggets.
In the U.K. you’re more likely to obtain pine needles when you have conifers growing nearby. I would caution anyone anywhere wanting to harvest from woodlands about taking care not to destroy wildlife habitat or disturb rare plants.
Pine needles provide a well drained and moist, springy layer – that’s good organic mulch. But you can expect an acidic reaction in the soil. U.S.A. gardeners seem less concerned about acidity problems – I sometimes wonder if this is marketing ‘hype’. But it may depend on the existing soil type, and the length of time over which they are used.
Pine needles are slow to decompose so they can’t be a major constituent in making leaf mold or garden compost.
An ideal place to use pine needles is under erica’s: heathers, azaleas, rhododendrons, camellias, peris etc… and around blueberries. Here they contribute to the soil type these plants love and keep their shallow fibrous roots moist. Fine pine needles might be tried around vegetables in summer as a slug deterrent but are best removed end of season.
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Nowadays lawn cuttings are being recycled directly onto the lawn by smart mulch mowers. Composting is another use for them. But you could easily have too much grass for composting. Whatever happens don't throw them away. Use as mulch on shrubs.
Lawn cuttings are a little messy to remove after placement, so I use them under trees, shrubberies and hedges. Most bulbs and corms: daffodils, hyacinth, tulips, crocus; will push through easily.
If you fork lawn cuttings into top soil don't forget to supplement the nitrogen content (see above
). Lawn cuttings are good for suppressing weeds, for feeding, heat insulating and retaining soil moisture.
Scatter in a layer no thicker than 1 inch. Problems can arise with thick compact layers that exclude oxygen from the soil surface. They’re probably not best placed over surface rooting plants like erica’s, rhododendrons, and the like. Of course lawn cuttings should not be taken from grass treated with hormonal weed killers
like feed’n weed.
These days, composted farmyard manure can be bought in nice 50L bags. In essence manure is a highly nutritious organic soil amendment. It is well applied to roses, and before planting potatoes, and nitrogen hungry greens – pumpkins, cucumber, cabbage, marrow...
It is well used as organic mulch in ‘no dig’ gardening. But it can equally well be mixed into the top few inches of soil.
Note that some manufacturers e.g. Westland; add lime. This makes their farmyard manure unsuitable for erica’s like rhododendrons and the like.
Raw farmyard manure includes: horse manure, cow manure, pig manure. Horse manure has a reputation for containing weed seeds. Pig manure rots down quickly. Cow manure is rather good because digestion is more complete. The manure is usually mixed with straw bedding, urine and other organic residues.
Raw manure should be left for 3 months to rot down. It’s best to protect it from rain under a tarpaulin or plastic sheet leaving room for ventilation. Composting increases the ph from acidic to more normal and stabilises the nutrient content.
Farmyard manure is best applied in late winter or spring.
STRAW AND HAY
Straw is a heat insulator to keep the soil warm and a barrier bed against infection.
It can be put down in autumn. It's especially useful when placed over delicate perennials for protection, and some more exotic plants such as tree ferns from colder winter climates. Used on greenhouse beds it helps to retain soil heat over winter. But I don't advise using under fruit bushes in cold weather.
Another important use for straw in summer is to prevent fruit contacting soil and becoming infected. Use straw around strawberries, courgettes, marrow, cucumber, melons, pumpkin etc... to prevent damage. It may also reduce slug damage.
Straw may be obtained in bales and blankets and layed down in single pieces. You can also get hold of loose straw as pet bedding. If you have loose straw you may find it necessary to hold it in place with string or coarse netting (fine netting can snag birds). The birds will take the straw for nesting material in spring.
A layer of straw in autumn followed by composted manure in late winter is a balanced combination of organic mulch.
Hay has similar properties to straw but is often more contaminated with weed seeds.
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WEEDS AND GREENTOPS
Hoed down and raked together into a pile, leafy weed tops can be left as mulch without a problem. You can also add vegetable green tops, carrot leaves, cabbage leaves. But I prefer to compost all these.
They do look rather untidy but fit into a herb garden area rather well. This method is also suited to raised bed ‘no dig’ gardening.
Uprooted and wilted weeds can also be used for mulch preferably before seed ripening.
Perennial roots like dock, dandelion, thistle can be included if exposed to the sun, likewise creeping buttercup if wilted. But I would not advise including perennial underground stems: couch grass, ground elder, nettle, bindweed…
Paper is organic and it rots down in the garden. It is good material for suppressing weeds and keeping the soil moist. A whole newspaper at least 8 sheets thick should be used with heavier material: compost, weed-tops, and straw; to hold it in place.
Newspapers are well applied to vegetable plots because you can easily plant through it. They are also popular for use around fruit and under trees. Gardeners also report using it successfully over surface planted potato tubers where it retains moisture for good growth. Weed suppression is the big advantage of blocking out the light. Spring is the best time to apply it.
Stock pile your newspapers and you have a cheap source of organic mulch compared to non bio-degradable plastic. The paper softens to a paper mash. This can be forked in adding organic matter to the soil and encouraging worms. However, limit the use of highly coloured magazine papers as the inks contain heavy metals.
Brown cardboard is effective at suppressing weeds because it excludes light. Obtained from shops as used packaging material, it is the free organic mulch alternative to using plastic sheeting.
Even perennial weeds will be hard done by with a layer of cardboard to contend with. As it breaks down over time it encourages earthworms, and unlike plastic sheet it will let the air and water penetrate.
If you haven’t had time to dig out perennial weeds then apply cardboard in early summer. It's a good way to tackle a large area. You need to carefully weight it down at the edges with soil, or bricks or, you could place loose mulch on top.
An edging of bricks with garden compost or farmyard manure topping up to the bricks is good. This can be done quickly and easily and even planted up. Adding a topping obscures the unsightly appearance of cardboard.
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Garden compost can be used as mulch around plants. You may sort out fine compost for working into soil, and for tomatoes, beans, potatoes for example. Then the remaining course compost is good for mulch. The tougher bits continue to decompose on the soil surface and soon disappear.
Garden compost behaves more like an additional soil layer than a covering blanket - it won’t have the insulating properties of more fibrous material and roots will tend to grow into it from the outset.
Do hot composting to ensure weed seeds are removed. One option is to use compost mulch as a stale bed, get rid of the weeds in the compost before removing and working into beds. The rhubarb plot is a possible place for this.
Garden compost is usually homemade but it can also be purchased locally.
BAGGED AND BRANDED COMPOST
Only the peat/peat substitute i.e. soil-less multi-purpose or potting compost is anyway suitable for mulch. These have sand, grit or even perlite mixed in, plus fertilizer, so it’s not ideal. Probably only feasible for small gardens and on limited areas – top dressing special shrubs.
Peat or peat substitute based compost, or ericaceous compost can be used more widely to mulch heathers, azaleas, rhododendrons, camellias, peris and the like; also blueberries and the like.
USED COMPOST FROM POTS, GROW BAGS AND CONTAINERS
Available end of season when plants are being thrown out. The same comments as for bagged and branded compost apply, except this time the material is cheap and can be spread around.
The compost behaves more as an additional soil layer than a covering blanket - it won’t have the insulating properties of more fibrous material and, roots will tend to grow into it from the outset.
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By Michael E. J. Scott.
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