ARTICLE - Understanding Soil

Soil is a living community, requiring a balance of components. Soil has microorganisms, nutrients, minerals, water and oxygen. All of these elements contribute to healthy plant growth. Good soil means well-fed plants that bloom more abundantly and produce bigger and longer-lasting flowers. Attention to your soil is the best way to make your plants look their best. It's easy to find out the quality of your soil - and it's easy to improve it.

A productive healthy soil that will support healthy plants has several characteristics. It needs to be deep, well structured, fertile, well drained and biologically active with a pH of 6 to 8. The combination of these features provides an environment that is ideal for plant growth.

There are three different types of soil. Consider the list below to determine yours. If you are still unsure, visit your local garden center. They are experts in your region's conditions and are there to help.

Clay soils have the smallest particles that hold together in a tight mass. If your soil sticks to your shovel, or if it becomes rock hard and refuses to absorb water when dry, you've got mostly clay soil, which can be hard for roots to penetrate.

Sandy soils have the largest particles that barely hold together at all. If water endlessly seeps into your soil, or if it is very easy to dig when wet or dry, you have mostly sand - which is often not very fertile.

Loam is a general word for near-perfect soil that has lots of organic matter, enough sand to be easy to dig in, but sufficient clay to provide fertility and solid anchoring for plants.

What Makes Things Grow

Fertile soil makes plants grow. Most soils need to be improved to make plants perform well and be more resistant to pests and disease.

Fertile soil is dark in color because it contains organic matter (such as Gardeners' Choice)- which has decomposed into a form that plants can use. Adding lots of organic material will reward you by producing faster growth on more beautiful plants and flowers.

You can add organic material to your soil any time you wish. Large quantities of organic material help cure heavy clay soils and fast draining sand and add micro-organisms and minerals to build up weak soils. Just remember that it doesn't last forever, so plan on adding organic material every year or so.

You can amend your soil in various ways:

  • Make your own compost or purchase soil amendment that is rich in organic matter.
  • When adding a new plant to your garden, work the amendment into the soil in the bottom of your planting hole and mix with the existing soil as you pack it around the root ball.
  • Improve the soil over an entire planting area by spading the amendment in several inches deep.
  • Cultivate the organic material into the surface of the soil around older plants that can use a boost.

What's going on down under?

To find out what's going on in your soil, dig a test hole two feet deep and look at the sidewall to tell if there is a lighter colored layer under the topsoil. Rich, healthy soil tends to be a darker color, so you can see.

To evaluate drainage conditions, fill the hole with water. If it drains away in an hour you have great drainage. If it takes a day you have slow drainage. If it sits overnight or longer, you have poor drainage. If you have poor drainage, add more organic material and try the drainage test again.

The pH scale indicates acidity or alkalinity. A soil with a pH number below 7 is acid, while one with a pH above 7 is alkaline. Garden plants typically grow best in neutral or slightly acid soil and you need not be concerned with pH unless your soil is one extreme or the other. Many good garden centers will gladly test a soil sample for pH levels for you, or you can buy an inexpensive pH test.

Acid soils are all soils that test lower than pH 7.0, which includes most soils east of the Mississippi River. In reality, most of these soils do not have significant acidity problems. Soils with pH levels below 6.0 may need special treatment or plant selection. Plants that will do well in acidic soil include Azaleas, Camellias, Rhododendrons, Blueberries and Japanese Maples.

Lime, available in either ground or powdered form, is often suggested to raise pH levels. Ground limestone is the slightly less potent of the two and raises pH more slowly. The amount needed depends on the soil texture (more is needed for clay than for sandy soil, for example). Or try adding your old coffee grounds to acid-loving plants.

Alkaline soils often occur in arid regions that receive less than 25 inches of rain per year. The majority of the soils west of the Missouri River are alkaline. Many plants popular for water-wise gardens do well in alkaline soil. The olive, native to the Mediterranean basin, is one example of a plant that thrives in alkaline soil; lavender and pomegranate also perform well.

To lower pH, ferrous sulfate and aluminum sulfate are often recommended. Ferrous sulfate, which also adds iron to the soil, is of the most help to plants that show yellow leaves as well as overall poor health. You'll also lower the pH of alkaline soil over time by regularly applying organic amendments such as compost.