Mark asks: I have a worm composting bin in a shady spot in my backyard. It was working well for a while. Now I have cockroaches in the bin. Will they harm the worms? Should I try to get rid of them?
Tropical Gardener answer: Cockroaches can be attracted to the food and decaying matter found in a worm bin. In reasonable numbers, they will not harm your worms. Worms regulate their population depending on the food supply. Insects that are feeding on the same material as the worms can cause the number of worms to decrease, however.
The most common roach species found in compost here in Hawaii are the American cockroach (Periplaneta americana) and, occasionally, the German cockroach (Blattella germanica). Though both have wings and are somewhat similar in appearance, the American cockroach is more prone to flying than the German one. The German species is sometimes used to compost in a system called blatticomposting. Check the internet for more information on that.
Roaches like areas that are warm, somewhat dry and undisturbed. If your worm bin is composting properly, it will be warm. If you are keeping it fairly dry, you might want to add moisture to discourage the roaches. It should be the dampness of a wrung out sponge. Be careful not to get it too wet or the worms will die or try to leave. Adding material and stirring up the contents of your bin frequently will also disturb and discourage the roaches.
If moistening and frequent stirring doesn’t chase them, you can try some repellent or nontoxic techniques. Bay leaves, cucumber and garlic can repel roaches.
Catnip is another natural cockroach repellent. Place sachets of catnip around inside your worm bin or simmer some in a small amount of water and make catnip tea. Spraying the tea in your bin, should encourage the cockroaches to move out but won’t harm the worms. If you add a little soap to the mix it will kill the roaches on contact.
Though both boric acid and diatomaceous earth can be used against cockroaches, it is best to keep boric acid away from your worms. You can put commercial boric acid roach tablets or baited sticky roach traps (both available at hardware and big box stores) in a dry spot outside your bin or go online for homemade cockroach trap instructions.
Of course, you don’t want to put toxic chemicals in your worm bin or even around it where roaches may carry them into the bin. The small amounts of boric acid they may carry should not be a problem. Food-grade diatomaceous earth is the only product that worm composters recommend against roaches and other insects that might move into your bin. It can be sprinkled in dry areas of the bin where roaches will come in contact with it. It will dehydrate and eventually kill them. Applying it regularly is best as it loses its efficacy after a few days or if it gets wet. Go to http://www.wormfarmingrevealed.com/diatomaceous-earth.html for more on using diatomaceous earth in a worm bin.
Email plant questions to konamg@ctahr.hawaii.edu for answers by Certified Master Gardeners.
Some questions will be chosen for inclusion in this column.
Diana Duff is a plant adviser, educator and consultant living in a dryland forest north of Kailua-Kona.
Gardening Events
Tuesday: “NRCS Irrigation and Groundcover Workshop” from 8:45 a.m.-noon at the UH Extension Service office in Kainaliu (across from the Aloha Theatre). Hands-on workshop on irrigation techniques, erosion controlling ground covers and NRCS assistance programs. Limited space. Registration required online at http://hawaiicoffee.weebly.com/nrcs-irrigation—groundcover-workshop.html or by calling Gina at 808-322-4892
Saturday: “Work Day at Amy Greenwell Garden” from 9 a.m.-12:30 p.m. Meet at the Garden Visitor Center across from the Manago Hotel in Captain Cook. Volunteers will be able to help with garden maintenance and are invited to bring a brown bag lunch. Water and snacks provided. Call Peter at 323-3318 for more information.
Farmer Direct Markets
Wednesday: “Sunset Farmers Market,” 2-6 p.m. in the HPM parking lot at 74-5511 Luhia Street in Kailua-Kona (across from Target)
Wednesday &Friday: “Hooulu Farmers Market,” 9 a.m.-2 p.m. at Sheraton Kona Resort &Spa at Keauhou Bay
Friday: “Pure Kona Market,” 9 a.m.-5 p.m. at Amy Greenwell Garden in Captain Cook
Saturday: “Keauhou Farmers Market,” 8 a.m.-noon at Keauhou Shopping Center
“Kamuela Farmers Market,” 7 a.m. -noon at Pukalani Stables
Sunday: “Pure Kona Green Market,” 9 a.m.-2 p.m. at Amy Greenwell Garden in Captain Cook
Tuesday-Saturday: “U-Pick greens and produce,” 10 a.m.-4 p.m. at Tropical Edibles Nursery in Captain Cook.
Plant Advice Lines
Anytime: konamg@ctahr.hawaii.edu
Tuesdays &Thursdays: 9 a.m.-noon at UH-CES in Kainaliu at 322-4892
Mondays, Tuesdays &Fridays: 9 a.m.-noon at UH-CES at Komohana in Hilo at 981-5199 or himga@hawaii.edu