Preparing for good performance Getting soil ready for planting

Preparing for good performance

Getting soil ready for planting

by Timothy Daly

One of the most common reasons for poor plant performance is the soil condition. Soil condition is one of the most critical components of a plant's environment because that is where it obtains water, nutrients, and air.

Often large sums of money are spent on

installing and maintaining plant material only to have some or all of the plants perform poorly. One of the most common reasons for poor plant performance is the soil condition. Soil condition is one of the most critical components of a plant's environment because that is where it obtains water, nutrients, and air. The ideal type of soil for a plant is fertile, deep, well-drained, and has a high organic matter. However, soils that have high fertility are not necessarily productive and vice-versa.

Roots grow where the conditions are favorable: where they have space amongst the soil particles, organic matter, and proper amounts of water and air for optimal growth. The roots that absorb the material are usually in the upper parts of the soil.

Soil texture is the fineness or coarseness of the soil particles. It plays a vital role in the soil's ability to hold water and provide oxygen to the plant's roots. > The largest of the particles is sand and its presence leads to coarser-textured soils. > Silt is somewhat smaller in size. > Clay soil is the smallest of the soil particles, giving the soil a finer texture. The texture classes are determined by the percentages of the three particle types, and the ideal soil has equal percentages of the three soil particles.

Macropores are large gaps between soil particles, usually filled with air. Micropores are small gaps, generally containing water. Sandy soils have more macropores and have fewer surface areas, allowing the water to drain away faster. Clay soils have more micropores, giving them a more significant amount of pore space. Due to their small size, the clay soil particles fit together tightly and have a greater surface area than larger sand particles. Thus, clay particles can hold more water and the small pore space retains it against gravitational forces. However, although clay particles hold water tightly, often the water is not available to the plants. Clay soils, being finely textured, are easily compacted. When soil particles are packed together closely, pore space and the movement of water and air are reduced. Compacted soils inhibit root growth, reduce the infiltration and the availability of water for the plant, and the limit movement of gases in the root zone.

Throughout many parts of Georgia, clay soils present a real challenge to the installation and maintenance of plant material. Due to the poor drainage and soil compaction, many plants will have a hard time growing in these conditions, which could potentially lead to their demise.

Exploring the options

Several options exist to mitigate the problem.

First, decide whether you would like to work with the soil or change its composition by adding amendments.

Some plants can tolerate growing in heavy clay soils better than others, such as forsythias, barberries, and some trees such as ash trees, elms, and willows, amongst others, as long as they have adequate drainage.

If you are going to plant trees and shrubs in clay soil, dig a hole roughly two to three times the soil ball's width from the container and no deeper than the top of the root ball.

Do not add soil amendments to the backfill. The roots will prefer to grow in the amendments and have difficulty making the transition to the surrounding clay soil, thus making the plant more susceptible to environmental stresses and pests. If you want to amend the soil, you will need to do it for the entire plantings area.

In many situations, changes are needed to grow the desired plants in clay soils successfully. > To improve poorly drained clay soils, deep till to break up the hard-packed soil layer several inches below the soil surface. To make substantial changes, you will need to add significant amounts of soil amendments such as sand, peat moss, composted manure, topsoil, or other materials. > Soil organic matter consists of decayed animal and plant residues, and adequate levels of it improve the soil's physical condition by allowing the water to infiltrate better, decreasing the loss of soil through erosion, and supplying the plant with nutrients. Organic amendments improve the soil tilth (the quality that allows you efficiently to work a soil into a loose state), allowing for better infiltration and drainage, often low in clay soils. Fresh organic material, such as leaves, wood chips, or manure, need to break down and decay before being added to the soil. Decomposing organic matter releases nutrients into the soil; however, nitrogen can become tied up and unavailable to the plant in the process of decaying organic matter. Make sure any organic matter you add to the soil is composted thoroughly.

Test for best results

Knowing the soil pH and fertility will also help improve clay soils for plant growth, and the soil can be tested through your local County Extension office. > Using an auger or spade, take a thin vertical slice of the soil down to the plow depth. For lawns, the sampling depth should be four inches. For vegetable gardens, ornamental plants, and wildlife plots, go down six inches.

> Take at least 15 to 20 core samples over the entire area and place them into a bucket that has not had fertilizer or other chemicals in it.

> Soil moisture levels do not directly affect the soil-test results but the soil should be slightly damp to dry, not wet. A rule of thumb is if the soil is too wet to till, then it is too wet to take samples. Moist soil is more difficult to mix and can damage the soil sample bag during shipment. > Place the cores in clean plastic or other non-metal buckets and mix thoroughly. The samples need to be mixed together to get two full cups that are dry for processing. > Take the soil samples to your local

Extension office, where you will obtain a sample bag. Place the soil in the sample bag to the fill line, then fold and fasten the top. Georgia's soils can be challenging to work in but can be managed to grow various plants. The key to working with clay soils is to use proper procedures to amend the soil and make the necessary changes to improve the soil tilth.

For more information on soil management, please contact your local Extension office or call 1-800-ASK-UGA1.