Q: I go out and water my plants when it gets hot, but they still look frumpy. Kay R., Paso Robles
A: You need enough water to get to as much of the root system as possible to make your plants happy. Plants need enough water to properly transport essential nutrients from the bottom of the plant to the very top of the plant.
To get water down to the very bottom or edges of your root system, you need to consider the type of soil you have and the depth and spread of your root system. If your soil is primarily clay, such as that found in North County and in San Luis Obispo, the soil holds more water, so it will retain more water.
Sandy soil, such as that found near the ocean, holds the least water and drains faster. Sandy soil has a penetration factor of about three times that of clay soil, so the water seeps more deeply but is not retained as much as in clay soil. To check the depth of water penetration, dig into the soil and determine how deep the water traveled.
The roots of a plant should have access to water at all times, but avoid overwatering and possibly drowning your plants. Watering should be done relatively infrequently, but deeply. The most effective watering should be done slowly. Quick, overhead watering is not as beneficial to plants. The best technique is the drip method. Installation of drip systems is not necessary, although very convenient, but a dripping hose or inexpensive hose timer may suit your needs.
The root systems of plants vary in depth, so a general rule of thumb is that leafy vegetables and annual bedding plants require 6 to 12 inches of water. Small shrubs, tomatoes, corn, and cool season turf grass requires 12 to 24 inches of water. Trees, large shrubs, and warm-season grasses require substantially more to reach deep roots.
Evapotranspiration factors such as temperature, wind, and humidity affect how much water your plants require, so have a chat with your local Master Gardener about your specific needs.
GOT A GARDENING QUESTION?
Contact the University of California Cooperative Extension Master Gardeners: at 781-5939 from 1 to 5 p.m. on Monday and Thursday; at 473-7190 from 10 a.m. to noon on Wednesday in Arroyo Grande; and at 434-4105 from 9 a.m. to noon on Wednesday in Templeton. Visit the UCCE Master Gardeners website at http://ucanr.org/sites/mgslo or email firstname.lastname@example.org .