Hi, do pyrethrum plants have to flower before deterring flies?

Hi Patricia 

Plants to deter flies include basil, mint, tansy, sweet woodruff, lavender, marigold, rosemary, and feverfew (a type of chrysanthemum daisy).

The pyrethrum plant helps repel aphids, but the dried flowers crushed and sprinkled around will help deter flies. Pyrethrum is the active ingredient in most fly sprays and insecticides, so it won’t hurt to plant it as a deterrent to garden insect pests.

Thanks, Tui Team.