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Composting Lawn Mowings that have been treated with herbicide

Composting lawn clippingsLawn mowings are an important ingredient of a home compost heap
They generate heat to make the heap work faster and they provide moisture. They should always be layered with more fibrous material like weeds or dead stalks so that they don't compact into a slimy mess.

Some lawn treatments contain herbicides that can persist for some considerable time, even when they have been through a composting process. This creates a dilemma for gardeners as these lawn clippings are not suitable for either home composting or to put into a green waste collection.

The herbicide clopyralid is the one most likely to cause problems for gardeners. It is a common ingredient of domestic lawn care products and is sufficiently persistent that it is banned in New Zealand and some parts of the U.S.A.

If buying herbicides, read the ingredients so that you know whether or not clopyralid is one of them. Also read the instructions carefully to find out how the manufacturers recommend that you dispose of the grass clippings. From February 2014 the labels on lawn care products containing clopyralid will have to read:
After treatment, leave the clippings from the first mowing on the lawn. The next three mowings should be composted well, for at least nine months, before being used as a mulch. Do not dispose of the grass clippings via council composting schemes.'

It is vital to follow these instructions.  Even better is not to use clopyralid at all and then you will have no problem.

If you employ a lawn care company insist on knowing exactly what their products contain. If they won’t tell you, you will have to decide whether or not to take the risk. Make sure that they are disposing of your lawn clippings responsibly, even if this incurs an extra charge.

If you are composting any lawn mowings that have been treated with a herbicide, or with a fungicide or moss killer, it is safest to compost them for at least one year, and preferably two, before using them in your garden. Council composting schemes are designed to work quickly and at high temperature but the speed of the process does not allow pesticides like clopyralid time to break down and cease to be toxic.

The simplest and safest course of action is to use no lawn care treatments at all and to enjoy a diverse lawn rather than a sterile monoculture.


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