Soil is classified based on the amount, by weight, and if it contains of clay, silt and sand. All soils contain these elements. However, how much your soil contains of each individual element determines what plants will thrive in your garden. Sandy soils contain more sand particles than silt or clay. Clay soils contain more clay particles than sand and of course silt (or loam) soils contain a balanced mix of clay and sand. Whatever type of soil your garden contains it can be improved with the addition of organic matter and the use of mulch.
What is the best soil?
Soil is made up of small particles of rock, water, air, decomposing organic matter and dissolved minerals. An ideal soil is an approximate mix of 50 percent solids, 25 percent liquid, 25 percent air and 5 percent organic matter. Loam soils (sometimes called silty or silt soil) come closest to this ideal of all the soil types. This means that any plant placed in loam soil will grow without additional nutritional or organic supplementation. Clay and sand make up the other soil types with clay having smaller particles and more liquid content than sandy soils.
However, before you start amending or replacing your garden's soil you must understand the best soil is the soil a plant will grow happiest in. Some plants prefer fast draining sandy soils while other plants sulk unless grown in nutrient rich clay soils.
Loam soils combine the best of clay and sandy soils. They hold nutrients and water like clay yet have better drainage and aeration thanks to sand particles. Loam soils are friable, that is they hold together well yet allow water and air to pass. Friable soils are said to have good tilth; this means they maximize root growth and are easy to till.
Loam soil has three types: clay loam, loam and sandy loam. Clay loam soils have more clay particles than sand particles and can become water logged and compacted. Clay loam is great for prairie and northeastern wildflowers, bramble fruits like raspberries and plants that require moist soil to thrive.
Loam soil is considered the ideal garden soil. Most plants will grow happily in loam soil as it combines the best of sandy and clay soils.
Sandy loam soil has more sand than clay particles and is fast draining and well aerated. Sandy loam soils are perfect for herbs, fruit trees and vegetable gardens as it holds nutrients, water and air, while still being fast draining, does not become water logged or compacted and allows easy penetration of roots.
Sandy soils are made up of large solid particles and contain little organic matter. These soils are fast draining and well aerated although most plants need supplemental fertilization to thrive. The large particles that constitute sandy soil allow for easy root penetration. Roots will grow longer and larger in sandy soils than in clay soils. Sandy soils are perfect for Mediterranean herbs, drought resistant or desert plants like Echinacea and cacti, and root vegetables. Most trees and shrubs do well in sandy soils as long as they are mulched to conserve water and fertilized regularly.
Clay soils have small particles and contain a lot of water and dissolved minerals. The small particles are tightly packed making it hard for air and roots to penetrate. If not worked carefully these soils become compacted. Clay soils do well with native wildflowers, shrubs and trees rather than cultivars (named varieties). Old fashioned (or antique) and shrub roses tolerate clay soil better than tea roses. Plants that like to grow in moist soil also thrive in clay soils.
Improving your soil
Adding organic matter in the form of compost, leaf mold or well rotted manure benefits both clay and sandy soils. Organic matter is made up of decomposed plants (including fruits, flowers and roots) or animal manures. Regardless of the type of organic matter you use it should be brown and crumbly and have a pleasant earthy scent. Adding organic matter to soil increases the variety of plants that will thrive in your garden.
In sandy soil organic matter adds nutrients and increases the soils water holding capacity. In clay soils organic matter separates the small particles allowing better air and root penetration as well as increasing drainage. Loam soils can also benefit from organic matter as it replaces nutrients absorbed by plants.
After several seasons of adding organic matter your clay or sandy soil will become as friable as loam soil.
- Taylor's Master Guide to Gardening; Houghton Mifflin Company; 1994
- The Garden Primer; Barbara Damrosch; 1988
- Four-Season Harvest; Eliot Coleman; 1999
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