Mulching is covering the ground with one of several materials to exclude light, which is an effective way of preventing weeds growing. Mulching the ground also helps to retain moisture and depending on the material used can help the fertility of the soil.
Some mulching materials such as black polythene are not very attractive and are more suited to places like an allotment or vegetable garden. Others, such as chipped bark can look very ornamental and can be used in gardens and borders.
This is one of the most effective mulches for eradicating weeds. When laid over the ground no light at all can penetrate and even the toughest of weeds will eventually die off.
The sheeting must be well anchored using bricks or other heavy objects to prevent it from blowing away in the wind. Black polythene is ideal for using between rows of fruit, before laying the sheet, cultivate the ground thoroughly and mound slightly towards the centre so that water will run off. Black polythene can also be laid over a larger area and planted through by cutting slits and planting plants the through it. This is ideal for Strawberries and Potatoes and can even be used on long term crops such as Brassicas. Laying polythene over a large area does have one drawback - watering. The best way to avoid this problem is to lay a seep hose under the polythene.
Grass clippings are a very effective mulch and can be applied straight from the mower box. However they must be applied as a 4" to 6" thickness and this can cause problems. If the layer is too thick, no air will penetrate to the bottom and they will become smelly and rotten and useless as a soil conditioner.
Experiments have been done in Sweden for 3 years on mulching Cauliflowers with grass clippings. It was observed that grass mulching consistently resulted in increased yield and reduced damage by root maggots. The effect of grass mulching on root fly population was also studied for 1 year. The mulching did not reduce egg laying but did result in increased egg-predation. The effects were most pronounced when the mulching material completely covered the ground even close to the stems of the plants.
Straw has similar qualities to grass clippings in that it has to be put down in a thick layer.
Peat, Compost and Manure.
These materials can be used for mulching and can be of quite an attractive appearance. They need to be laid in a 2"- 3" thick layer. Manure should be well rotted before laying or damage can occur to plants. All three will benefit the soil fertility. One drawback though, is that if not applied in a thick enough layer, weeds will thrive even better with the extra feeding that they get.
This is the most effective method in the ornamental garden. Bark is available in various grades of coarseness, all of which have the same effectiveness and it is only a choice of what appearance you wish to have. It has to be laid to a thickness of 3" to be effective. The only disadvantage is the price; it tends to be more expensive. It can also be used for making pathways, which, if laid to a suitable thickness, will resist weeds for a number of years.
Paper and Biodegradable Polythene
These products are made to break down after a period of time. Lay the product down and plant through it. Once the crop has been gathered it can be dug into the ground where it will rot down. The paper products tend to be slightly better as the polythene once tend to break down into strips, which can blow about.
Newspaper is a cheap but more time consuming method. Lay 6 sheets of newspaper ion top of each other and anchor down. The paper tends to go fairly firm once it has been wet and dried out again and forms an effective barrier. Once the crop has been lifted, the newspaper can be dug into the ground.
These can be laid to a thickness of 3" and can look quite attractive when used in a border. The only disadvantage is that you have to gather them yourself.
Home Made Mulches
If you have a shredder or chipping machine for getting rid of garden waste, you can use this waste as a mulch. Use the same way as Bark.
In an experiment on an organic farm in the UK mulching with different green manures was compared using the yields from subsequently grown wheat crops to evaluate the effectiveness of the different green manures.
The plants used were three different leguminous green manures - Red Clover (Trifolium pratense L.), White Clover (Trifolium repens L.) and Trefoil (Medicago lupulina L.) and a non-leguminous rye-grass (Lolium spp.). All were cut at a height of 30-40 cm and left on the soil surface as a mulch. Over one year, White Clover accumulated the most dry matter but Red Clover the most nitrogen (N). Both yielded more dry matter and N than the Trefoil and the Rye grass.
The yields of the subsequently sown wheat varied. The spring sowings 6 and 18 months after green manuring yielded poorly but the winter wheat one year after green manuring yielded well when following both the Red and White Clover. Yields following the Trefoil and Rye Grass were not as good. It was concluded that overall Red Clover was the best species for use as a green manure.
© copyright 1999, P. A. Owen