| (Find out more at a Water Efficient Workshop)
Inspect Your Soil
A thorough analysis of both the physical and chemical characteristics of the soil is important when developing a water-wise landscape. Georgia has a wide variety of soil types, ranging from well-drained coastal sands to poorly drained clays. Each soil has its own unique structure and texture, drainage pattern, pH, nutrient content and need for amendments and fertilizer. To complicate matters, an individual landscape may have several different soil types, or the soil may consist of fill dirt brought onto the site. Soils are seldom perfect; most of them can be improved in some way to ensure best plant growth.
Soil Analysis Saves Guesswork
Before landscaping, take a sample of your soil to your local county Extension office for testing. Your county Extension agent will provide you with a recommendation for lime and fertilizer based on the analysis.
Do Not Add Organic Matter to the Planting Hole for Trees and Shrubs
For years we have added organic matter such as peat moss, animal manure or compost to the planting hole to enrich the soil, to conserve moisture and to improve plant growth. But recent research shows no benefit from amending the planting hole. In fact, organic matter added to individual planting holes in clay soils acts like a sponge in a bathtub, holding excess moisture around plant roots after irrigation or rainfall. Wet, waterlogged soils that suffocate plant roots are a leading cause of plant death in Georgia. Even in well-drained soils, organic matter encourages the roots of plants to stay within the hole instead of growing out to explore the native soil.
When planting individual trees and shrubs, dig a large planting hole, at least two times wider than the root ball of the plant. Research at the University of Georgia shows that plants transplanted into a large planting hole establish themselves more quickly and develop a significantly larger root system than those in a small hole no larger than the root ball. A large, extensive root mass improves the plant's ability to absorb moisture from the soil and helps the plant survive drought. Next, make certain the top of the root ball is level with the soil surface, then backfill with the same soil removed from the hole. Do not add amendments to the hole. Simply backfill with the native soil after removing stones, sticks and other debris. Tamp the soil lightly to eliminate air pockets. Water thoroughly and then add organic mulch, such as pine straw or bark ships, to the soil surface to conserve moisture. When planting a group of shrubs, cultivate the soil throughout the area as deeply as possible. Cultivation changes the structure of the native soil and provides a good environment for root growth.
Improve the Structure of Poor Soils
Certain native soils, like dense, poorly drained clays, have such poor structure that plant growth suffers unless they are improved. Poorly drained soils can be improved in several ways. Sometimes deep cultivation will break apart a hard layer of soil (hardpan) several inches below the soil surface and improve drainage. Another option is to bring in additional soil to raise the planting area 12 to 15 inches above the existing grade. Some professional landscapers also incorporate 3 to 6 inches of a coarse aggregate, such as granite sand, into poorly drained soils. A final option is to install subsurface drainage pipe to carry excess water off the site after rain.
On the other hand, soils that tend to dry out rapidly and hold little moisture will benefit from organic matter such as aged animal manure or compost, incorporated uniformly throughout the planting bed. This is particularly helpful when water-requiring plants, like annuals, are to be grown. However, instead of adding the organic matter to the planting hole, apply 3 to 6 inches on the soil surface and incorporate it into the soil. Your goal in soil analysis is to create an ideal soil environment for the expanding root system. An ideal soil has good aeration and drainage, yet holds adequate moisture and nutrients for optimum root growth. Research at the University of Florida shows that the roots of trees and shrubs grow outward approximately seven times the diameter of the root ball during the first growing season when provided with a good soil environment.
Unfortunately, no cookbook recipe exists for soil improvement. How you treat the soil depends on the characteristics of the native soil, the type of plants to be grown and the time of year when planting.
Before planting, check the structure and texture of the native soil by digging a hole 12 to 15 inches deep and examining the soil horizon. Is it loose and granular or hard and compact? Fill the hole with water and watch how fast it drains. If water remains in the hole after 12 hours, the soil is poorly drained.
Plants prone to drought stress, like azalea, dogwood, annuals and herbaceous perennials, prefer a moist, well-drained soil; plants known to be drought tolerant, such as crape myrtle, ligustrum and juniper, will grow well on very dry sites once established. Likewise, soil prepared for summer transplanting when dry periods are likely to occur should have a greater water-holding capacity than soil prepared for fall transplanting when rainfall is generally more regular and irrigation demand is low.
Water-absorbing polymers, commonly called hydrogels, are popular new products. These man-made crystals, sold under various trade names, absorb several hundred times their weight in water and gradually release it to plant roots. One pound of crystals applied to 100 square feet of bed area will absorb 20 to 25 gallons of water, or about 50 times as much moisture as peat moss. They last from six months to several years in the soil, depending on product.
Research to date with hydrogels is limited and has provided conflicting results. However, preliminary studies with hydrogels at the University of Georgia shows them to enhance the growth of summer annuals in nonirrigated soils. Another potential use for hydrogels reported by professional landscapers is in container plants to extend the time between waterings.
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