It seems that cats love orchids. And it seems to be a common problem with them eating them. So, although there isn't a spray to keep them away (wouldn't that be convenient) there are things you can do to stop your cat from eating your orchids or other plants.
You can usually find sweetgrass at your local garden center in 2" or 4" pots. Cats find this yummy and it will distract them from eating your orchids.
Another option is to put a small amount of cayenne pepper around the plants. Note that this can only be done for a short amount of time like 4-5 days to discourage your cat. After that it should be washed away otherwise it could be harmful to the plant.
Does anyone have any other suggestions?
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How to Grow the Most Breathtakingly Beautiful Orchids