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Purdue University
Consumer Horticulture

Department of Horticulture and Landscape Architecture

What is Loam?

Released 01-06-00
by B. Rosie Lerner, Extension Consumer Horticulture Specialist

Gardeners are often advised that a loamy garden soil is best for just about all plants. But just what is a loamy soil?

Soil is composed of many particles of varying sizes. Soil scientists have classified soil particles into three major groups: sand, silt and clay. Sand particles are the largest and tend to hold little water but allow good aeration. Clay particles are very small in size and tend to pack down so that water does not drain well and little or no air can penetrate. Silt particles are medium sized and have properties in between those of sand and clay.

A loamy soil, then, is one that combines all three of these types of particles in relatively equal amounts. Loamy soil is ideal for most garden plants because it holds plenty of moisture but also drains well so that sufficient air can reach the roots.

Many gardeners complain of their garden soil being compacted and/or poorly drained. Heavy, compacted soil can be rescued by the enduring gardener. Add a good amount of organic matter, such as compost, animal manure, cover crops or organic mulch materials, each year as the soil is worked. It may take several years, but eventually the soil compaction will be improved. Although adding some sand along with the organic matter is acceptable, adding sand alone is not advised. The organic matter offers several advantages that sand does not, including increased water- and nutrient-holding capabilities, in addition to improved aeration.

Highly sandy soils can be a problem since they do not hold much water and few nutrients, as well. Adding organic materials to a sandy soil will improve its ability to hold water and nutrients. You'll need to add at least a two-inch layer of material to make a marked improvement. This translates to about 17 cubic feet of organic matter to cover a 100-square-foot area.

And remember that soil improvement is a program, not just a one-shot deal. You'll need to continue applications at least once a year for several years to really change the nature of the existing soil.

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Site last updated: 10 April 2006

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