If your mom likes to cook, clear a small patch of land and plant it with herbs like basil, thyme and mint. If you don't have land, terra-cotta pots work just as well! She will love harvesting the fresh herbs.
Another idea for all moms: Plant a lavender garden by the backdoor so every time the warm summer air blows she is captivated by the sweet scent. Make a little wooden sign (you can get one from a craft store) and write on it, "Mom, each year you grow more wonderful."
More gift ideas for Mom.