Gardeners often wonder if inexpensive play sand, sold for children’s sandboxes, can improve garden or potting soil. While using sand for drainage is a correct impulse, the type of sand is paramount. Using play sand for horticultural purposes is strongly discouraged. Its specific composition often creates the opposite of the intended effect, leading to serious problems for plant health. This negative outcome results from the fine particle size and shape, which differs fundamentally from the coarse sand or grit required for soil amendment.
Understanding Play Sand Composition
Play sand is typically made from silica or quartz, a mineral base that is inert and safe for plants. The material is heavily processed, screened, and washed to remove impurities and larger fragments. This processing results in particles that are very fine and uniform in size, generally ranging from 0.15 to 0.75 millimeters in diameter. The grains are sub-angular to sub-rounded, unlike the jagged particles of horticultural grit. These rounded grains pack together tightly, reducing natural air pockets between them. Trace amounts of very fine silt and clay particles, often called fines, also remain. These fines contribute significantly to the material’s ability to compact into a dense mass.
The Goal of Adding Sand to Soil
Gardeners primarily add sand to soil to improve drainage and aeration, especially in dense, clay-heavy beds or fine-textured potting mixes. Healthy soil requires a balance of solid particles, water, and air; air spaces are crucial for root respiration and water movement. Sand is intended to increase macro-pores—the large spaces between soil particles that allow water to drain quickly and air to circulate freely.
To succeed, the sand must be coarse, with large and irregular particles that resist settling. This coarse material physically separates finer particles, preventing clumping and creating a stable, porous network for the exchange of oxygen and water around the roots.
Why Fine Sand Harms Soil Structure
The fine, rounded nature of play sand makes it unsuitable for improving soil structure because it works in opposition to creating macro-pores. When fine sand is mixed into soil containing smaller particles, such as clay or peat moss, the small sand grains do not create new air pockets. Instead, they simply fill existing macro-pores, significantly reducing the volume of air space.
This process leads to severe soil compaction, often described as creating a concrete-like mixture. The fine sand and clay particles bind tightly, forming a dense matrix that is impenetrable to water and air. This hard, suffocating medium prevents water from percolating, leading to waterlogged lower layers and poor oxygen availability for the roots. Root growth is physically restricted, and the constant moisture in the compacted soil increases the risk of fungal diseases and root rot.
Recommended Alternatives for Drainage
To effectively improve soil structure and drainage, choose materials with coarse, angular, and non-uniform particles. These characteristics ensure the particles interlock, creating stable air pockets and resisting the compaction seen with play sand.
Horticultural Grit and Sharp Sand
Materials known as horticultural grit or sharp sand are made from crushed rock, such as granite or quartz. This provides the necessary jagged edges and larger particle size. Coarse builders’ sand, often used in construction, can also substitute for horticultural sand, provided it is clean and free of salt or lime impurities.
Volcanic Materials
Other effective alternatives include perlite and pumice, which are lightweight, porous, volcanic materials. Perlite is an expanded volcanic glass that is extremely light and holds air well, making it excellent for aeration in potting mixes. Pumice is similar but denser, and both materials function by preventing the finer soil components from collapsing into a dense mass.