• What is Soil?
• Soil Structure
• Soil Tests
• Improving Drainage
• Increasing Water Retention
• pH in Soils
• Soil Nutrients
• Soil Amendments
• Living Soil
• Mulch
• Native Soils

What is Soil?

Topsoil is comprised of rock, minerals and organic matter. Most of the fine, inorganic matter is merely weathered rock. The organic matter is plant and animal materials in various stages of decomposition.

Topsoil is the fertile uppermost layer of soil, ranging from a thin layer to a foot or more indepth. It is different from subsoil primarily because topsoil has organic matter, especially humus. Humus is a dark organic material of finely decomposed plant and animal materials.

The inorganic fraction of soil can be separated by particle size. Sand has the largest particles. It contains lots of porous airspace, but water and nutrients leach through quickly. Silt is next in size between 1/100th and 1/10,000th of an inch.

Fine silt can lack vital airspace. Clay is finer yet, and both air and water can have difficulty penetrating the fine particles. When dry, clay is hard and unworkable. When wet, it is sticky and equally unworkable.

A workable soil that allows penetration of water and porosity of air contains similar amounts of sand, silt and clay. This type of soil is called a loam.

Soil Structure

Healthy plant growth depends on more than a rich soil and water. Soil structure is just as important as nutrients.

A hard soil inhibits moisture penetration and drainage. A soil that becomes too dry or too wet will damage fragile plant roots. In addition toxins can build in the soil.

A good topsoil is approximately 50% soil and 50% airspace with half of the air spaces filled with water.

Soil Tests

If your soil is home to a garden of lush, diverse plants (including weeds), you probably do not need to test your soil unless you intend to plant exotic plants.

If you decide to test your soil, be sure to take several samples from a wide area. Avoid touching the soil or using tools or containers contaminated by other sources.

You may wish to consider testing your soil yourself, using test kits available from your local nursery or hardware store. This can often give you a general idea about the condition of your soil. If necessary you may wish to take a soil sample to a laboratory for a more detailed analysis.

Improving Drainage

The use of organic matter can loosen clay soils. Inorganic materials, such as sand and gypsum are often used. Sand, while far less expensive than gypsum, should be used in equal portions with clay or with organic matter. Inadequate amounts of sand can actually worsen drainage problems by binding with clay particles.

Inorganic amendments will not decompose, so they will last for many years or even permanently. Organic amendments release nutrients and create an environment for many beneficial insects and microorganisms to live.

Increasing Water Retention

The large pore spaces in sandy soils prevent water retention. The soils dry out easily and leach precious nutrients past plant roots.

The addition of organic materials can help with water retention and increase nutrient availability. Clay can also help increase a sandy soil's water retention. Pumice and Vermiculite are beneficial as well. Super-absorbent polymers dramatically increase water-holding abilities in soils, but are very expensive.

pH in Soils

Acidic soils are common in rainy areas with sandy soils. Some plants like a slightly acid environment and others prefer a slightly alkaline soil. Soils low in pH can have calcium, magnesium and phosphorus deficiencies. A soil high in pH can lock up many nutrients, especially iron, from plants. Higher pH soils tend to have higher salinity levels as well.

Few plants can survive beyond a 4.0-8.0 pH range; 7.0 is neutral. If you need to lower the pH in your soil you can add sulfur. If you need to raise the pH you can add lime. Organic materials can also affect pH, but for a much shorter time than sulfur or lime. Materials such as redwood, peat moss and leaf mold will lower the pH. Compost and ash are alkaline and will increase your pH.

Soil Nutrients

Synthetic fertilizers are inexpensive and easy to use, but they are easily overused, dissipate quickly and do not offer a wide range of nutrients that an organic soil amendment brings. Fertilizers also do not help in developing soil structure or creating a living soil for your garden.

In organic amendments the nutrients often vary. As a rule, animal byproducts, such as fish emulsion or manure, are high in nitrogen.

Organic matter, such as compost from the green parts of plants, usually has fairly high levels of nitrogen as well. Organic matter derived from woody materials, such as sawdust, while low in nitrogen, do have other nutrients and provide critical structure to soils.

Before choosing a soil amendment or fertilizer, determine what your needs are. If you are looking for a quick greening or blossoming of your garden, then a synthetic fertilizer may be what you need. If you are looking for a long-term release of nutrients or have soil porosity problems, then you may want to add an organic amendment.

Soil Amendments

Organic amendments decompose and eventually disappear, so you will need to add new amendments from time to time. The amendment will last much longer than synthetic fertilizers, which disappear as quickly as a few weeks. It is important to remember that a healthy soil needs care. In nature plants grow, bloom, die and recycle back into the soil. This is nature's way to add organic matter back into the ground.

A good soil amendment includes material from both woody plants and either the green parts of plants or manures. This allows for the development of a balanced humus that will provide both nutrients and long-term soil structure.

When applying soil amendments, it is best to work in amounts of about 2 inches in depth. Tilling is better than hand mixing unless it is a very small area that you are working with.

A Living Soil

All soils have micro and macroorganisms. Most of these creatures are beneficial. They help nature's process of recycling between life and death. They also help in creating soil porosity by tunneling and churning organic matter into the soils.

Unfortunately, pests exist in every garden. Perhaps they are snails or nematodes or anyone of a multitude of other organisms that seek to dine in the luscious restaurant of your garden.

Many insects beneficial to the soil are often considered pests. Good examples of these are termites and ants. It is not a good idea to exterminate all living creatures that you see in your garden, but only those you know will be harmful.

The first step to control insects is regular turning of the soil so that the air and sun expose eggs and larvae. Encouraging birds can also be a help. If you have a little infestation, do not over react. When you spray, you kill good and bad creatures indiscriminately. Your short-term solution may create long-term problems.

Mulch

Synthetic mulches have increased in popularity over the years. Most are effective in preventing soil compaction and retaining soil moisture.

The disadvantage of synthetic mulches is that they do not decompose and release organic matter and nutrients into the ground.

An organic mulch mimics a plant's natural environment. All plants drop leaves, branches, etc. onto the ground. This is nature's natural mulch and it will eventually decompose into the earth. Sometimes the decomposing mulch can become a breeding ground for pests, but it also can become a breeding ground for beneficial creatures that will enhance your garden. If there is a problem, the mulch can be turned over, mixed into the ground or removed. Preferably, it should be left for nature to refertilize and cushion the soil.

Inorganic mulches are often used, such as gravel or lava. For plants that prefer an arid or semi-arid climate, these mulches can be a preferable alternative to moisture-retaining organic mulches, such as bark.

Native Soils

The most important thing in developing a thriving garden is to work with the environment you live around. Do not plant forest-loving plants in an arid environment or vice versa.

You may prepare the soil, provide the proper moisture and sun, but your efforts may still be in vain. Mother Nature will reclaim your hard work in days, months or years. Work with the environment you have and cultivate native plants. Your soil can be enhanced to improve your plants, but drastic changes from your native environment means lots of hard work.

That doesn't mean exotic plants will fail. It merely means that you must be selective. If you live in a dry, arid climate, plants from South Africa, Australia and the American Southwest may flourish. If you live in a wet, hot climate, plants from the tropics may flourish. Find the native environment of the plants you want and see if they are compatible. However, consider that your garden is not a single climate. One side may get more shade or sun, retain more or less moisture or have a different soil. Oftentimes a house site may have several microclimates in addition to the native climate of the area. Work with what you have and enhance it.