As a Hedgewitch, plants and herbs are a staple in my practice, but this holds true for many paths. Plants, herbs, crystals and stones add extra oomph to your workings, an extra kick, if you will.
Gardening isn't that difficult, it just takes dedication, like working your path does. Soil, sun and water makes a garden grow. Love and care nurture the garden to true magnificence.
I read over the following website and indeed the plants mentioned here would make an excellent Witches Garden. Books like Complete Encyclopedia of herbs by Scott Cunningham will help you decide what plants and herbs you need for what type of working.
Here is the link:
http://balconygardenweb.com/how-to-create-a-witchs-garden/
