Mix 1 to 2 tablespoons of Dr. Bronner's LIQUID peppermint castile soap in 1 quart of water. Fill a spray bottle and use on your outdoor plants. Will not harm plants. Dr. Bronner's liquid peppermint castile soap can be purchased in health food stores.
Thanks for the tip about Dr Bronner's liquid peppermint soap; I will give this a try. I usually use dawn dish soap but will try your suggestion to see if it works better. Thanks.