Making compost with grass cuttings

We have been talking about composting recently, particularly about how to do it and what ‘recipes’ to use. In UK gardens there is often a lot of grass cuttings through the summer which provide the ideal base for an active compost bin. By active I mean one that gets above 40C.

Grass in a council green bin two days after cutting

The problem is that grass cuttings will start to compost on their own. Although grass will heat up quickly it soon runs out of air and the temperature falls. The grass then forms a dense stinking mass which does not breakdown.

Layers of partly rotted grass cuttings in a badly managed compost heap

The answer is to mix grass with bulky material like shredded twigs or straw. This allows more air to get to the grass and provides carbon to balance the nitrogen which keeps the compost going.

After a few weeks the temperature will begin to fall because the air in the pile has been used up. Time to turn the heap to allow more air to enter. The temperature should rise again but probably not as high as before.

For more information on what to mix with grass cuttings to get the correct C:N ratios, carbon or browns to nitrogen or greens see this page. For an online C:N ratio calculator  follow this link.

The other important thing to get right is the moisture content;  it should be around 55% or like a wrung out sponge. Not easy to gauge but not dry nor soaking wet.

To compost kitchen waste we use a Hot Bin. There is around a small bin full of stuff every week and I usually add some grass cuttings and chopped twigs. This is the temperature in the Hot Bin a couple of hours after adding new material and giving it a stir. Eight hours later it had risen to 46°C.

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