Drought – Supplemental watering

Q: You recently wrote that even with our drought, supplemental watering isn’t generally needed in the winter. What are some guidelines as to when I should re-start watering my camellias and azaleas?

A: Water loss from the soil is caused by three things: evaporation, gravity, and transpiration (plants sucking it out). In winter, spring and early summer, evaporation is low. Gravity pulls surplus water from the soil but it stays moist. Transpiration is low because the plants aren’t growing very fast, at least in winter and spring. But as things heat up in June and July, water moves out of the soil faster than rainfall can replenish it. Around the first of July, your soil begins losing approximately 7/8 inch of water per week. Your shrubs don’t need watering before that point, but as the soil drys, in the absence of rain, you need to add water to make up for what’s lost. For established shrubs, I wouldn’t restart watering until late June, and then, only to supplement normal rainfall.