Recently Green Action Centre has been receiving calls from people who complain that they have unwelcome visitors living in their compost pile. While the solution to getting rid of these little pests is not always simple, the solution to keeping them out in the first place is.

Generally the existence of mice/vole or wasp nests is an indicator that your compost pile is too dry. With the heat and lack of precipitation we have been experiencing this summer, it is not surprising that compost piles are dry. Remember that your compost pile should be about as damp as a rung out sponge. You also likely need to stir or turn the pile to ensure that the moisture is distributed throughout. If the pile is moist and aerated, it will build up the kind of heat that will make it an inhospitable environment for mice and wasps.

I recently came back from a few weeks of holidays only to find wasps were just beginning to set up shop in my compost pile. I wet the pile down, left it overnight (hoping to avoid getting stung) and then turned the pile. Wasps gone!

If wasps have however settled in for the long haul, you may have to explore other options. I would still recommend that the first order of business be to wet the pile down and leave it for a few days. To reduce the risk of getting stung, do this at night when the wasps are less active.  Wetting your pile may get it heating up again and convince the wasps to leave, however I wouldn’t hold my breath. If they seem to give up residence, then you can stir the pile and go back to normal. Normal of course means monitoring the pile a bit more often to make sure it does not get too dry and stirring it from time to time. If they don’t, unless you have a bee keeper’s suit or similar protection, you may have to wait until late fall when they die off and then stirring the pile thoroughly.

Mice or voles present a different and sometimes more difficult problem. They won’t sting you, but they definitely can leave you squeamish. I have been composting for over 20 years in Charleswood. My cat brings mice home regularly and leaves them as a gift for me on the deck or patio, but I have never had them in my compost pile. Keeping the pile working (hot) is the key. If they need air conditioning to keep their home cool, they will leave and find another place that is naturally cooler.

Here are some other ideas on getting rid of these little critters:

  • Aerating the pile thoroughly each day for 3 or 4 days will disturb the nest and make residency less desirable.
  • The mice or voles may be burrowing under your bin so look for any tunnels around the edges and flood them with water. They will collapse but if they reappear again keep flooding them.
  • Avoid the use of poisons as they can also be ingested by pets.

Another option for keeping mice out of your pile is to Pest Proof it. If you have a molded plastic bin you could place ¼ inch wire mesh under the bin to keep them from tunneling in. You will want to wrap the wire over the bottom lip of the bin as well as make sure that it is on level ground and pinned down solidly. If you have a wood bin pest proofing is a bit more difficult. You can line your bin with a similar mesh and make a mesh lid, however gaps in the mesh at corners can be an issue. Click here for details on pest proofing your wood bin.