Types of Garden Mulches

Different mulches, impenetrable and loose

Polythene sheets are a great aid to weed control but unsightly, costly in cash and environmentally undesirable. They vary in manufacture and use. The clear polythene, similar to that used for polytunnels, can be pinned to the ground to warm up the soil in spring and encourage flushes of weeds.

Black or opaque polythene sheeting, thick enough to exclude all light, warms the soil and kills weeds – even perennials. It can be laid permanently and covered with a loose mulch to improve the appearance, so becoming suitable for shrub borders, soft fruit and other permanent plantings. In the same way, it can be underlayered in gravel paths and drives.

If all perennial weeds are dead it is a good idea to puncture plastic sheets in many places to prevent water problems. Unperforated, they may cause flooding or a lack of aeration to the soil. Pre-perforated sheets can be bought ready made, but then of course cannot, unaided, prevent weeds passing through. Black and white polythene can be reversed, after the black side has warmed the soil and killed weeds, for the white side to reflect light up on to the plants and confuse pests.

Large squares of polythene tucked into slits round the edge make a superb start for young trees, keeping them weed-free and preventing evaporation for a year or two. Long strips a stride or so wide are excellent for starting hedges, cuttings of easy rooters, such as quickthorn, can even be pushed through them. Strips of polythene can also be used for strawberries, vegetables and particularly lettuce and saladings which then get less dirty, though slugs may become more of a problem.

I do find the sight of polythene mulches unappealing and with high winds there is a danger of them and the crop blowing away in the open. Woven materials are also available and are similar to perforated polythene, but are heavier. Their porosity allows much better aeration of the soil and less water run off than with impermeable polythene. Woven materials are far more expensive than polythene, but are better for growing valuable crops through like strawberries where their wear resistance will also be useful. Bed-sized pieces on the vegetable plot will kill and incorporate green manures for many years and are tough enough to have flaps cut for planting through.

Carpet is the best woven material, heavy, weed resistant and not unattractive laid upside down and often available free. This is the material for breaking new ground – even a bramble can’t push through a nice bit of Axminster or Wilton. Purely artificial carpets last forever and make good paths, especially in the fruitcage and polytunnel. The brighter ones can look much better covered in a skim of loose mulch. Organic wool or cotton carpets rot after a year or two of use, so are perfect for establishing trees and shrubs. Mixed fibre carpets partly rot leaving a stringy mass to dispose of.

Paper and cardboard are no good on their own except in the greenhouse or polytunnel where they are safe from wind and useful for keeping lettuce and saladings clean. Outside they blow away unless covered with another mulch. Used in this way, they kill many weeds almost as well as plastic or fabric materials, but rapidly rot. Using them under a loose mulch stops birds mixing weed-seed infested soil into the mulch material. They improve the effectiveness of thin plastic sheet which lets some light through. Wet them first to get them to lie flat.

Types of Garden Mulches Peat, bark and coir are very much more attractive to look at than any other mulches. Peat is considered undesirable in the UK, but on a world scale it is abundant and an excellent material. Bark by-products are better for the UK as we produce these, coir and other wastes are also replacing peat, but all are very similar. They do not add much to soil fertility and are very expensive compared to the others. However, they are generally weed-seed free, of good texture and beneficial to most plants. Because of their cost, they are best used for important ornamental areas, but would be advantageous almost anywhere. They can be made to go further if used on top of newspaper or cardboard and improve the appearance of plastic mulches. On their own, at least a finger’s depth is needed and this will need topping up every year. Do not use thin layers -they just disappear – and hold down fine-grade material with a coarse-grade top layer to prevent it being blown around in the wind. Do not put thin, loose mulches down unaided on top of weeds, as the weeds will just grow through.

Compost, well-rotted muck and manures are applied more for their fertility than just as mulches. Sieving beforehand makes them more attractive, but is laborious and they; inevitably are full of weed seeds. This makes them most use on the vegetable bed and around trees and shrubs. In thick layers, they suppress many existing weeds, but not creeping or vigorous ones. These mulches disappear quickly and so need continual topping up.

Straw and hay may be available in quantity and make good mulches under trees and in the fruit cage, especially for strawberries. There tend to be quite a lot of annual grass seeds after these mulches, so be prepared to keep mulching once you start. Best on top of a newspaper layer, a threeinch-thick slab of straw or hay will then last for two years or more and look quite attractive as the colour mellows. Put on loose, these materials are good for covering less hardy plants in severe weather, bracken fronds are better. Take care with mouldy straw or hay and with bracken as inhaling dust from these can be a health hazard.

Grass clippings are freely available, home grown and for the asking. Put down in one place they make a wet smelly mess, but put in inch layers and topped up regularly they make one of the very best mulches. They feed the soil and encourage worms, so benefit almost every area of the garden. Multiple layers are good for earthing up potatoes and soft fruit bushes and trees. Grass clippings ‘glue’ down the edge of polythene sheets and can help disguise them as a skim on top. They can be made more effective and longer lasting if put down over newspaper.

Sand and gravel are not usually thought of for mulching; however, they do have many advantages though adding no fertility. They can be very attractive and are cheap and sterile. They keep moisture in the soil, but do not get wet themselves which makes them good for winter protection of less hardy plants. One of the best mulches for ornamental areas and for fruit where they reflect up ripening heat and light. Sand is excellent for asparagus, but should be darkened with soot or it will not warm up quickly enough. Be warned – anything seeding into gravel germinates, so practise good preventative hygiene nearby. It is a good idea to put gravel over perforated plastic confining the worms and soil underneath.

06. January 2011 by admin
Categories: Compost and Manures, Weed Control | Tags: | Comments Off on Types of Garden Mulches

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