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As long as all the plant material, leaves, roots and seeds are removed; it should be no issue planting other plants in your garden.

Yes, they are toxic to cats. There is one thing about cats that should be noted as important. They are strictly carnivores. They do not typically eat vegetation, but sometimes young kittens can be tempted to chew on the wrong things. Most cats will leave it alone, but it is poisonous to cats.

All this being said, it is often used as a repellent. Cats will not usually eat something that is toxic to them. So although it is toxic, there is little chance of a cat actually eating this.

This article will offer some more information: https://www.gardeningknowhow.com/plant-problems/pests/animals/cat-repellent.htm