Boosting Drought Tolerance
It's all about helping the roots grow strong and deep, the foundation
of a plant that will thrive during dry periods. So how can you influence
a plant to grow the kind of roots you want?
Give roots their ideal surroundings
Deep, loose, well-aerated soil is essential for root growth and drought tolerance. Air is a kind of "fertilizer" that makes any plant grow more strongly.. Make "air spaces" your first priority.
Prepping the soil
Dig at least 20" deep and add bone meal (high in phosphorus.) Adding organic matter is fine if you're planning on growing winter-wet tolerant plants. Just be sure you can guarantee plenty of air spaces.
When transplanting from pots, tease out the roots as much as possible, prune any crossing or tangled roots and take off some of the top growth to match. You don't have to cut it back completely, just remove leaves to reduce the demand for water.
To persuade roots to grow deep rather than wide, plant seeds or small plants into "tree pots," about 8" to14" tall, or use deep, 20 oz compostable coffee cups, about 7" tall.
Avoid compacting soil by walking on it or leaving it empty, without roots to "till" the bed
Gradually withhold water
Nurture plants with plenty of water and fertilizer the first year. In their second summer, withhold water to encourage deeper roots, especially in August and September.