Most garden plants get their moisture from the soil layers near the surface. Only a few plants—mainly grasses and trees—have roots that can reach down into the deeper layers.|
But the surface layers of soil are constantly losing water. The plants take it up through their roots and release it through their leaves during the day, particularly in hot weather.
Also, as the sun heats the ground, moisture evaporates. Dry winds also cause evaporation. These sources of water loss are at their worst in hot climates with long, dry seasons and where water is scarce and expensive.
|Below are suggestions and techniques for keeping the soil moist. By following these points you'll keep watering to a minimum and the watering you do will meet the water requirements of the plant roots instead of evaporating.|
Water holding capacity of various soil types
When you wet soil, the water penetrates according to the soil type and structure. Each soil type has a holding capacity. It will retain a certain amount of water and allow the rest to sink deeper. For example, dense clay soil holds more water than porous sand.
Until the holding capacity of a layer of soil is exceeded, no water will sink to the next layer. Because of this, any watering you do may only penetrate the first 2 or 3 inches, leaving the soil beneath dry. In addition, dense soil won't accept water as quickly as porous soil. Heavy watering may only create rivers that flow into the gutter and leave much of the soil dry. The answer to this dilemma is proper soil preparation and following some simple rules.
Watering guidelines Sandy soil: One inch of water penetrates 12 inches into sandy soil.
Loam (i.e. organically rich soil): One inch of water will penetrate about 6 to 10 inches into this type of soil.
Clay: One inch of water will only soak the top 4 or 5 inches of this thick soil.
Effect of soil structure on water penetration
Differences in soil structure also affect water penetration. If you lay topsoil or humus on a different kind of native soil, the water is likely to go as far as the boundary line between the types and then just sit or flow away to the side.
The same thing happens when you place a nursery plant in a hole and put your garden soil back in the hole around the root ball. Water outside the root ball won't go in, and water inside won't go out. And since roots only go where there's moisture, they may never grow out of the original nursery soil.
For all these reasons, you should amend the soil. Amendments help to lighten dense soil, hold water in porous soil, and create a transitional zone between the soil types.
Deep soak for proper root growth
If you water for a brief period each day, you will only wet the upper few inches of soil. This happens because you haven't watered enough to exceed the holding capacity of that layer of soil and force water down. The roots of your plants will stay in the moist upper layer.
Because moisture evaporates quickly, you'll waste time and water using this method. And, if you forget to water or there's a hot spell in July, you may lose a lot of plants. Another drawback of frequent watering is that it encourages growth of weed seeds, fungus, and disease organisms.
Light watering makes shallow roots
Remember that light watering makes shallow roots and a hot spell may damage your plants. Deep watering sends roots down into the cool soil where moisture is retained longer. Also, mulch around your plants to retain moisture.
Plan your watering
The best general watering plan is to soak the soil deeply and not water again until the top few inches of soil begin to dry out. Plant roots will extend into deeper soil where they stay cool, and any weeds at the top won't have a chance to grow.
If you have dense soil, water slowly so the water has time to penetrate. It may take hours for water to reach the 12 to 18-inch level. To be sure it has, wait a day or two, then dig up a spadeful or take a core sample. Check the moisture content and then plan your future watering based upon what you find.