Q: My husband put several tablespoonfuls of boric acid on my crown of thorns and a gardenia, trying to kill ants. Now these two houseplants are suffering greatly. Is there anything I can do to rescue them?

A: Boron is an essential nutrient for plants but only in very tiny amounts. Just 1 part per million can be toxic to houseplants. Although boric acid is a fine insecticide, using it as you’ve described was a bad idea. Boric acid is very soluble in water, so your best bet is to wash the soil from your plant roots and repot them with fresh potting soil. If they continue to decline, discard them. My wife advises that dinner at a nice restaurant always helps her forget boneheaded things I’ve done to her plants.