Help for the Home Gardener from the
Contra Costa Master Gardeners' Help Desk
The client has put a lot of veggie pulp in their compost bin. They have also added a lot of orange peels. This has attracted a large number of fruit flies. The client has covered the compost with about six inches of pine needles and leaves but this has not gotten rid of the fruit flies. The client wants to know what more can be done.
Master Gardener Response:
These flies are not harmful, but can be quite a nuisance when you get clouds of them in your face on lifting the lid of the bin! Very often, even a well-managed bin will have a few of these creatures. One way to minimize them would be to build the pile all at once, then turn frequently so the process runs hotter. The compost will generate heat which will kill or reduce the numbers of fly maggots. Here is a UC link which explains this process. http://anrcatalog.ucdavis.edu/pdf/8037.pdf. You can also save your kitchen scraps in the freezer until you are ready to add them.
If regular turning of the bin is not something you want to do, you could start by protecting the kitchen waste container from flies, as they can lay their eggs there which are then transferred to the compost bin. One helpful tip is to line the waste container with newspaper. When you take the scraps out to the compost, wrap them up completely in the paper and bury them under the surface of the bin. Don't add a lot of pulp material at once, especially citrus, as this is more likely to attract the flies. Pine needles are fine in the compost, but I would be wary of adding large quantities, as they are quite acidic.
I would also advise checking the moisture level of your bin. If the compost is too wet, the flies are more likely to be attracted to the rotting material. If this is the case, you should add more browns such as shredded leaves, cardboard or newspaper.
I hope that this information will help you with your fruit fly problem. If you would like any further information on composting in general, or on worm bins, please do not hesitate to contact us again.
Happy Composting,
Contra Costa Master Gardeners' Help Desk
Editor's Note: The CCMG Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. (map) We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, and we are on the web at http://ccmg.ucanr.edu/. "Ask a Master Gardener" help tables are also present at many Farmers Markets as well as at the CCMG's "Our Garden" programs (map). See the CCMG web page for details/locations.