Watering Wisdom (cont)
By: National Gardening Association Editors
Slow and Steady
Water slowly for best results; think of a gentle summer rain that lasts for several hours. Water applied slowly will seep into the soil where it can be used by plant roots. Water applied with a heavy hand, or during a downpour, often runs off rather than soaking in. This is not only a waste of water, but can also lead to pollution problems if fertilizer is contained in the runoff and finds its way to a lake or stream. Soaker hoses minimize runoff, but there are other ways to help, too. For example, create a "donut" of soil around new plants by mounding soil into a low, circular berm several inches from the stem or trunk. This creates a shallow bowl where the water you apply will puddle and soak in slowly, rather than running off. Once plants are established, flatten this berm so water drains away from the plant. If necessary, install a pressure regulator to lower the flow rate of sprinklers or soaker hoses so water is applied slowly and gently.
How Much is Enough?
Both the frequency and amount of water required will vary with your climate, soil, and plants' needs. Shallow-rooted annual flowers need more frequent, lighter waterings than deep-rooted trees. Heavy clay soil retains water better than sandy soil. The best way to determine how much water to apply, and how frequently to apply it, is to use a shovel. After watering, use the shovel to remove a wedge of soil in the garden or lawn. The soil should be moist to a depth of at least six inches for annual plants, and 12 inches for perennials, shrubs, and trees. Most of the roots plants use to take up water are located in these zones. (Don't forget to replace the wedge of soil.)
A timer is useful to turn on and off your sprinker. You can then begin keeping records of how long it takes to moisten the soil to the desired depth and set the timer accordingly. For example, a weekly two-hour watering might be just right for your perennial bed or lawn, while your annual planting may need just 15 minutes.
Between waterings, use your shovel again to determine when to water again. Remove a wedge of soil; if it's dry three inches down for annuals, or six inches for larger plants, it's probably time to water again, unless a soaking rain is predicted.
Amend Soil and Apply Mulch
Interestingly, adding organic matter to soil helps it absorb and retain water, while also improving its drainage. Mix in organic matter at planting time and use organic mulches, such as bark chips or pine straw; as they decompose they'll add organic matter to soil.