Answer: There are many recipes for deterrents, but vinegar is not recommended as it can damage plant tissues -- in fact it is occasionally used as an herbicide.
Here are some you might try, but be sure to test them on a few leaves first and wait a few days to make sure the plants will tolerate your concoction well.
Mix into a quart of water: one clove garlic (chopped), one
onion (chopped), 1 teaspoon Tabasco sauce, 1 Tablespoon
cayenne pepper or chili powder, 1/2 teaspoon dishwashing
liquid. Dribble over area to be protected. Be sure to wear
rubber gloves and be careful not to get this in your eyes or
on your skin.
For squirrels and other critters: Some gardeners report success using repellent
sprays, either home made garlic/pepper recipes or the
commercial type such as GetAway Squirrel and Raccoon
Repellent or even predator urines. Others report that a pet dog or cat can
serve as a deterrent, and others resort to a combination of
methods including caging plants that seem to be particular
favorites. If digging is their main activity, you may find that a
wire mesh such as chicken wire laid over the surface or caging the plants can be helpful.
Luckily cosmos bloom more when picked regularly, so they should regrow quickly.
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