Watering can hurt your plants. Don’t be surprised: Watering habits must take the soil into account, or plants can suffer from what seems to be a reasonable amount of water. They can even drown.
When you water, you really aren’t watering plants; you are watering the soil. In turn, the soil becomes the reservoir from which plants obtain the water. So soil is the key to how much and how often to water.
The two typical Colorado soils are not well balanced. One is sandy, the kind that feels gritty when rubbed between fingers. The other is clay, the type that sticks to shoes. Each has distinct characteristics that require different watering techniques.
Sandy soil allows water to flow through quickly. Little water is retained for plants to take in. Sandy soil also contains plenty of air, which is vital to the health of the plants, but it dries out quickly. It must be watered frequently to keep it moist enough for plants.
Clay soils are trickier. They resist water penetration, so water flows through very slowly. Water binds tightly to the clay and is not readily available to plants. Because it doesn’t seep away, water can actually suffocate a plant. Clay must be watered infrequently, to allow the soil to dry out.
Adding organic matter can create the mix of air and water that puts sandy or clay soils in balance. A 1-inch layer of well-aged compost is a great start. Till it into the soil at least 4 inches, but 8 inches if you can.
With this soil amendment, the seepage in sandy soil slows down, and water is available for plant roots. This lets you water less frequently.
In clay soils, the organic matter creates voids between particles that can fill with water and air. But most of the benefit to clay comes from the encouragement of microorganisms that cause the particles to clump together. In both types of soil, microorganisms introduced with compost make nutrients available to plant roots.
Applying compost restores and maintains a soil’s balance. And once balance is attained, plants will thrive on less water, less often.
David Winger is a water-conservation specialist with Denver Water.
