Horticultural Grit can be a gardener’s best friend in preventing compact and waterlogged soil! How does one use them effectively? Finally, is it horticultural grit or is it horticultural sand?
Horticultural Grit is composed of crushed rocks, mainly silica, limestone, quartzite, or a few others. Such stones are 1) extracted from the ground, 2) crushed, 3) washed to remove other soil content, and 4) placed in sturdy bags for delivery. This results in sharp-edged grains 1-6 mm in size which are used to improve drainage and aeration in soil by loosening its mixture.
Which horticultural grit is best for you and your plants has a lot to do with what plants you have and what soil they are in. It’s never a bad idea to see how you can improve your garden by looking at every aspect which may influence its growth.
Horticultural grit is often mixed in tandem with other growing mediums to achieve the desired balance between water retention and drainage. Incorporating horticultural grit makes the soil more porous, preventing soil compaction.
Mixing it with conventional growing mediums such as loam, vermiculite, clay, sand, potting mix, or others can significantly improve drainage and aeration. This enhances the strengths of the growing medium or mitigates its weaknesses.
Horticultural grit offers some unique benefits which make it a good fit for gardeners seeking to optimize plant growth by improving the soil. As with anything, it does have some pros and cons.
Horticultural grit is beneficial to gardening soil because 1) make the soil less compact, 2) improve aeration and drainage, 3) dries out quicker, 4) it is inorganic, 5) it is long-lasting, and 6) lime-free and not lime-free versions are available for better control of the pH level.
On the other hand, the main problem with horticultural grit is its high price compared to the individual material it is made of. The washing treatment it undergoes is the process that adds to the price.
In general, it is recommended to use 50 g of horticultural grit for every 1 liter of soil. This guarantees the best compromise between drainage and weight of the overall soil volume keeping costs down.
The mixing is the easy part. The hard part is knowing which plants require more drainage than others. As a general rule, succulents and cacti prefer a grittier soil mix since they do not require much water. Indoor plants also require more drainage to prevent instances of overwatering.
The components of horticultural grit vary from manufacturer to manufacturer but mainstream options are either predominantly made of or are a mixture of 1) limestone, 2) silica, or 3) quartzite.
However, we do not think that these minor differences in components would make much of a difference since they all share the same function of aiding aeration and drainage by improving the soil structure.
Limestone is a hard sedimentary rock composed of calcium carbonate or magnesium carbonate. It is very useful in gardening soil and a mainstream component of horticultural grit because of its unique property of neutralizing soil acidity and filtering other harmful substances from the soil.
High acidity makes it difficult for plants to absorb nutrients in the soil. Limestone is a source of lime (calcium oxide). This substance neutralizes the acidity of the soil to stable levels, making the nutrients more readily absorbed by the plants.
Silica is another important component of horticultural grit because it is vital for plant growth and development. It improves cell strength and cell structure rigidity. This leads to greater pathogen resistance, better water and nutrient uptake, enhanced metabolic functions, and increased environmental resistance.
While not an essential nutrient like Nitrogen, Phosphorus, and Potassium (NPK), silica is a good additive to any growing medium. They function how vitamins tablets are to the human body but applied to the plant world.
Quartz (man-made) or Quartzite (natural) is the last among the three main components of horticultural grit. They are useful in gardening because they help keep the soil together, preventing it from being washed away easily. Quartz is a metamorphic rock formed predominantly by interlocking mosaic quartz crystals.
Quartz often carries silica with it which dissolves in the soil which aids plant cell rigidity. Other substances also form from the silica carried by the quartz.
These substances have beneficial effects on the soil. Opal acts as a binder that keeps soil particles together. Kaolinite also forms from the silica in the quartz which acts as a surface for adsorption for organic matter and metals.
The main difference between horticultural grit and horticultural sand is the particle size. The particles of horticultural grit (between 1-6 mm) are larger than those of horticultural sand. Note that horticultural sand is coarser and with larger particles than beach sand.
Despite the minor technical differences, they both function in the same manner which is to improve aeration and drainage in the soil. These coarse mediums are often mixed with soil to loosen it, allowing roots to easily penetrate and for water to drain unimpeded.
For some gardening stores, horticultural grit and horticultural sand are often used interchangeably. The term used in Europe is “grit” whereas “sand” is used in the U.S. Regardless of the confusing naming scheme, the actual physical properties of the product are more important than what they are labeled as.
Horticultural Grit has coarser and larger grains than sharp sand, which lends itself better gardening. Sharp sand, also known as builder’s sand, is finer, and primarily used for construction.
Sharp sand is a cheaper choice if you are working over a larger space but is not as effective as horticultural grit for indoor or gardening in a more limited space. Compared to horticultural grit, sharp sand is often not washed which means it still has some silt and clay content which makes it less optimal for gardening.
Apart from its practical use of improving soil structure, horticultural grit has the added benefit of improving the aesthetic of the soils and the pot. The lighter colors of crushed stone and their larger size contrasts nicely with the dark, earthly tones of soil.
Clear glass lends itself well to this kind of aesthetic endeavor since the soil structure can be seen. Horticultural grit can be mixed with the soil or have its own separate layer. Horticultural sand can also be used to the same effect to create several, distinct, multicolored, and multi-textured layers.
If you’re eco-conscious, you can always use recycled glass or mason jars which also serve the same purpose. Mason jars are especially common and readily available. Maybe you can find some lying around in some dusty garage or underneath the sink!
- Horticultural grit is a simple and easy way to increase aeration and drainage in soil.
- It is made up of crushed stones such as quartz, limestone, silica, or other similar stones which are subsequently washed to clean it of other impurities.
- It can also be mixed with other growing mediums for either functional or decorative purposes. For the latter, clear glass is good since the decorative soil structure is on full display.
- “Dissolution and formation of quartz in soil environments: a review” by Michael Jeffrey Wilson in Soil Science Annual 71(2):3-14
- “HORTICULTURAL GRIT 1-4MM” by n/a in Stone Warehouse UK
- “Limestone” by n/a in ScienceDirect
- “Limestone: Who, What, Why, When, and How?” by Dr. Vanessa Corihher in Texas A&M Agrilife Extension
- “Physical Properties of Soil in the Murrumbidgee and Coleambally Irrigation Areas” by J. Hornbuckle and E. Christen in CSIRO Land and Water
- “Tarmac Soil Conditioner Horticultural grit 12L” by n/a in DIY