A plant is considered drought tolerant if it can survive a dry spell of more than 2 or 3 months without supplemental watering. This means that most native plants from regions that occasionally experience 2-3 months without rain are drought tolerant.

To reduce the need for  irrigation in your landscape, choose drought tolerant plants. If you want to eliminate watering plants altogether, select species native to your area.

LINKS:

Backyard Gardener

University of Rhode Island Green Share

BOOKS:

Xeriscape Plant Guide: 100 Water-Wise Plants for Gardens and Landscapes

The Green Gardener's Guide: Simple, Significant Actions to Protect & Preserve Our Planet