How do I compost grass clippings

10:29 - 23 August 2011

When the summer grass is growing strongly it needs mowing once or twice a week to keep it in trim. Trouble is that this means you could end up with gallons and gallons of grass clippings, especially if you have a large garden.

If you only have a small garden or only generate a bucketful of clippings a week these can be mixed with shredded paper, shredded cardboard or woody prunings and added to the compost heap. If you add too much grass in one go you will end up with a slimy smelly mess in the compost heap.
You can rectify this by taking it all out and layering it with dry material, but it is better and also much easier if you do this to start with.

If you have a large lawn you will be generating huge amounts of grass clippings on a weekly basis. The good news is that large amounts of garden waste can be used to create what is known as a hot heap. This is a composting system that reaches high temperatures and composts quickly. It gets hot enough to kill most weed seeds and also most garden diseases. The bad news is that you will need to have copious amounts of dry, woody material, leaves, shredded paper or cardboard to mix with it and plenty of room too. If you can layer the grass clippings with layers of cardboard and leave this tiered heap to break down then it should heat up with the action of the microbes and break down quickly. The cardboard soaks up excess moisture and once the heap starts to cool, worms will move into the moist cardboard. You basically need equal parts of wet material (grass clippings or general garden waste) and dry material such as shredded paper, cardboard, dry leaves, shredded woody stems etc. It’s a bit like making a cake; you need the right balance of eggs and flour to get the right consistency.

Make sure your compost heap is open to the ground so that excess liquid can drain off as the heap processes, this also allows beneficial creatures to move in and out of the heap depending on the temperatures.

If you have treated your lawn with chemical moss or weed treatment you need to be aware that these may persist in the compost and affect your garden plants, refer to the packaging of the treatment to see how long the grass clippings must be composted for before using the compost in the garden.

Some gardeners use fresh grass clippings as a mulch. If they have been treated with weed or moss killers this is a bad idea as these chemicals are persistent and will affect your plants. Uncomposted grass clippings will also generate what is called nitrogen snatch, where the microbes breaking down the material will grab nitrogen from the soil to fuel the decomposition process, thus starving the plants for a short period. It is better to compost the grass first and then use the composted waste as a soil conditioner or garden mulch. Freshly clipped grass may also spread weed seeds around the garden.

Another way
If you still have a huge quantity of grass to dispose of then it’s time to think outside the box. Reduce the amount of lawn you have and grow flowers or vegetables. Buy a mulching mower that cuts the clippings really finely and pushes them back around the grass roots, which mulches the grass plants and reuses the clippings to feed the lawn. Or cut the lawn very regularly and leave the clipping son the surface to break down. Alternatively grow your lawn into a meadow that you cut twice a year. Dry the hay and use it for animal feed or animal bedding provided it hasn’t been treated with chemicals.

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