Issue: June 29, 2002

Boric acid in garden to kill roaches?

I read that boric acid can be used to kill roaches. Can I use boric acid in my flower beds to keep the roaches from coming indoors?

Boric acid is effectively used as an indoor treatment for roaches. Use only boric acid whose container is labeled for roach control. As roaches crawl through an area treated with the powdered boric acid, it collects on their legs and body. As the roaches later groom themselves, they will ingest the boric acid and die.

Boric acid is intended for indoor use, not outdoor use. Boric acid can kill your plants as well as it can kill roaches. The boron in boric acid is a nutrient needed in very small quantities by plants. Even a little too much boron is toxic to plants. Most of our Southwestern soils have adequate concentrations of boron, and additions of boric acid can quickly create a toxic situation.

Salt to kill snails?

I have seen snails killed when salt was sprinkled on them. Can I use salt to kill snails in my garden?

This is another case of a product that can kill plants. Snails do die when salted, but so do plants. Sodium is another plant nutrient used in very low concentrations by plants and toxic to plants at slightly higher levels.

Fertilizer will do the same thing to snails and slugs as table salt will do. You can sprinkle a little fertilizer on them and they will die. The fertilizer won't hurt plants unless you overdo the snail treatments. Too much of any salt (and fertilizers are salts of plant nutrients) will harm plants. Fertilizers are nutrients that don't become toxic as quickly as boron or sodium. A band of fertilizer placed several inches from tender plants after irrigation will help protect from snails following irrigation. For severe snail and slug infestations, it is better to use other methods to control snails to avoid over-fertilizing the garden and harming the plants. Other methods include the stale beer snail/slug traps and chemicals labeled to kill snails and slugs.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!