PRODUCTIVE GARDENS ARE BUILT ON WELL-STRUCTURED SOIL.
Structure, by definition, is an arrangement of the elements of something complex. In gardening, the complex something is soil, and the elements are its basic constituents: sand, silt, and clay particles.Soil structure describes the degree to which these particles are grouped together in stable clusters or “aggregates.” Soils with good structure—often equated with good tilth—are soft, loosely packed, crumbly, and friable. To anyone who has gardened in heavy clay, such an ideal may seem an impossible goal, yet there are some basic steps gardeners can take to improve soil structure.
Well-structured soil has three major attributes: Its aggregates are diverse in content (with a mixture of sand, silt, and clay) as well as in shape and size; the spaces or “pores” between the aggregates are thoroughly interconnected by channels; and the aggregates remain stable when exposed to water. The water and air that are essential for healthy plant growth easily infiltrate well-aggregated soil. Plant roots readily penetrate the open channels, developing deeper and more complex systems and giving plants better access to the nutrients in the soil.
How do soil aggregates form in the first place? A variety of dynamic effects—wetting and drying, freezing and thawing, infiltration of roots, and the action of soil organisms—loosen soil and orient individual sand, silt, and clay particles to each other in a way that encourages the formation of clusters. As earthworms and soil microorganisms break down organic matter, they produce gums, waxes, and other gluey substances that bond the particles together into strong, water-stable aggregates. These gluey compounds are part of what makes up humus, the stable end product of organic matter decomposition. Aggregates are not to be confused with clods, the hard, dense lumps ofsoil that can form when wet soil is worked.
Unlike soil texture, an innate property determined by a soil's parent materials, structure can be improved by good management practices—or degraded when soil is poorly managed. Mulches and cover crops add organic matter to soil and protect soil from the surface-crusting impact of raindrops. Gardeners should avoid unnecessary tilling, which breaks aggregates and exposes soil to erosion and the loss of organic matter. Walking on or working soil when it is very wet or dry also harms soilstructure.
The organic substances that bind soil particles together are susceptible to degradation, so it's important to replenish your soil's organic matter—add compost! The organic matter in compost, and the by-products of the life cycles of soil denizens that feed on it, force the tightly packed particles in clay soil apart, improving drainage. In sandy soils, organic matter takes hold in the large pore spaces and acts as a sponge, slowing drainage so the soil stays moist longer. And with more moisture, sandy soils can hold the water in which plant nutrients dissolve, making these nutrients more available to plant roots. In sand, clay, and all types of soils, adding compost is the key to healthier plants.
Structure, by definition, is an arrangement of the elements of something complex. In gardening, the complex something is soil, and the elements are its basic constituents: sand, silt, and clay particles.Soil structure describes the degree to which these particles are grouped together in stable clusters or “aggregates.” Soils with good structure—often equated with good tilth—are soft, loosely packed, crumbly, and friable. To anyone who has gardened in heavy clay, such an ideal may seem an impossible goal, yet there are some basic steps gardeners can take to improve soil structure.
Well-structured soil has three major attributes: Its aggregates are diverse in content (with a mixture of sand, silt, and clay) as well as in shape and size; the spaces or “pores” between the aggregates are thoroughly interconnected by channels; and the aggregates remain stable when exposed to water. The water and air that are essential for healthy plant growth easily infiltrate well-aggregated soil. Plant roots readily penetrate the open channels, developing deeper and more complex systems and giving plants better access to the nutrients in the soil.
How do soil aggregates form in the first place? A variety of dynamic effects—wetting and drying, freezing and thawing, infiltration of roots, and the action of soil organisms—loosen soil and orient individual sand, silt, and clay particles to each other in a way that encourages the formation of clusters. As earthworms and soil microorganisms break down organic matter, they produce gums, waxes, and other gluey substances that bond the particles together into strong, water-stable aggregates. These gluey compounds are part of what makes up humus, the stable end product of organic matter decomposition. Aggregates are not to be confused with clods, the hard, dense lumps ofsoil that can form when wet soil is worked.
Unlike soil texture, an innate property determined by a soil's parent materials, structure can be improved by good management practices—or degraded when soil is poorly managed. Mulches and cover crops add organic matter to soil and protect soil from the surface-crusting impact of raindrops. Gardeners should avoid unnecessary tilling, which breaks aggregates and exposes soil to erosion and the loss of organic matter. Walking on or working soil when it is very wet or dry also harms soilstructure.
The organic substances that bind soil particles together are susceptible to degradation, so it's important to replenish your soil's organic matter—add compost! The organic matter in compost, and the by-products of the life cycles of soil denizens that feed on it, force the tightly packed particles in clay soil apart, improving drainage. In sandy soils, organic matter takes hold in the large pore spaces and acts as a sponge, slowing drainage so the soil stays moist longer. And with more moisture, sandy soils can hold the water in which plant nutrients dissolve, making these nutrients more available to plant roots. In sand, clay, and all types of soils, adding compost is the key to healthier plants.