Potting soil or growing media, also known as potting mix or potting compost (UK), is a substrate used to grow plants in containers. The first recorded use of the term is from an 1861 issue of the American Agriculturist. [1] Despite its name, little or no soil is usually used in potting soil.
Materials used for growing mediums include: peat, coconut coir, wood products like bark and wood fiber, perlite, stone wool, soils/tufts, and recycled paper and cardboard. [2] Other materials used include rice hulls, sand, vermiculite, and calcined clays. [3]
Typical potting mixes include one or more materials which retain moisture, one or more materials which aid in aeration and drainage, and fertilizer. Moisture-retaining materials and aerating materials can be combined in any ratio, depending on the particular needs of the plant. Soils are minimally used as growing media because they compact and lose pore space after repeated watering and can be too heavy for growing potted plants. [4] Mediums used for growing plants in pots typically are a mix of organic and inorganic ingredients. [5]
Good growing mediums have a number of properties including moisture and nutrient retention capacity, quick water infiltration, pore space for aeration (plants roots need oxygen), drainage for excess water, decompose slowly, and provide support for the plants growing in them. [5] They also have an optimal range of pH, cation exchange properties, and lack substance that are toxic to plants [5] These are also dependent on the type of plant grown since there is wide variation in moisture and nutrient needs among different plants.
This part is usually made up of peat (usually with limestone to reduce acidity) [6] or coconut coir. It serves to absorb water and nutrients. Tree bark, mainly of pine, may also be used.
The use of peat is controversial since the harvesting of peat moss from peatlands (which includes unique habitats such as bogs and fens) can degrade these peatlands. Peatlands are home to a diverse range of plant and animal species. Peat also has a very slow accumulation rate, as little as 1mm per year, so they take a long time to regenerate. Peatlands are also carbon sinks, constituting 3% of the world's surface but storing up to 30% of the carbon sequestered in the soil. [7] The removal of the layer of CO2 absorbing plants releases CO2 into the atmosphere, contributing to climate change. [8] [9]
As such, alternatives such as coconut coir are promoted by some organisations. [10] [11]
Sand and grit may be used for drainage and aeration. Perlite and vermiculite improve both aeration and water retention.
All plants need essential plant nutrients to grow, so it is important to make sure there is a sufficient amount in the potting soil. [12] Some nutrients may be already present in the bulking ingredients. [13] Peat contains 1% nitrogen that is almost never released. Limestone (for raising pH) contains mostly calcium (calcite), but can also contain magnesium (dolomitic). The latter is preferred as it supplies both elements. A typical proportion of limestone to peat is 8.5 pounds per cubic yard (5.0 kg/m3). [13] Coir contains a high amount of electrolytes (salts). In fact, untreated coir contains too much sodium and potassium for plant growth, so it is washed and then buffered (partially replacing salts with other minerals, usually calcium and magnesium) to produce the growth medium. Vermiculite contains some calcium and magnesium, but more importantly it helps retain water and nutrients in the porous structure.
Nutrients not supplied by the bulk will need to be supplied by the fertilizer. In conventional mixes they may be slow-release formulae of synthetic fertilizers, while organic mixes will use organic source such as compost (e.g. leaf mold, bark compost or recycled mushroom compost). Overuse of fertilizers will, as with in normal soils, risk damaging the plant. [13] For compost, the maximum recommended amount is 1 part compost to 1 part bulking material. [14]
A soil test may be done to analyze the chemistry of a potting mix, despite the mix not necessarily being made of soil. As an approximation for indoor home planting, the mix is generally treated as greenhouse growth medium. The main method is a saturated media extract (SME), which tests the chemical contents of a water extract of the mix. [13] [15]
| Analysis | Acceptable, min | Optimum, min | Optimum, max | Acceptable, max |
|---|---|---|---|---|
| Soluble salt, mS/cm [lower-alpha 2] | 0.75 | 2.0 | 3.5 | 5.0 |
| Nitrate-N, ppm [lower-alpha 3] | 40 | 100 | 200 | 299 |
| Phosphorus, ppm | 3 | 6 | 9 | 18 |
| Calcium, ppm | 80 | 200 | — | — |
| Magnesium, ppm | 30 | 70 | — | — |
The growth medium should be adapted to each plant's (and growth stage's) preference for aeration, drainage, nutrition, and pH. [14]
For seed starting, a "germination mix" is typically light-weight and suitable for starting small-seeded plants. A "seed starting" mix is suitable for larger seeded crops. [17] Following early growth, most plants prefer a potting mix that is more well-draining.
Cacti and succulents require sharp drainage, thus requiring a much larger percentage of perlite or sand. [18] Carnivorous plants, such as the Venus flytrap and the pitcher plant, prefer the nutrient-poor, acidic soils common to bogs and fens, [19] while water-based plants thrive in a heavier topsoil mix. [20]
Commercially available potting soil is sterilized, in order to avoid the spread of weeds and plant-borne diseases. [21]
As with garden soil, potting soil can attract insects. For example, the fungus gnat is often found around houseplants because it lays eggs in moist potting soil. [22]
Infections of Legionnaires' disease due to potting mix have been reported in Australia, [23] New Zealand, [24] the Netherlands, [25] the United States, [26] and Japan. [27]
Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical, and biological properties. It is commonly prepared by decomposing plant and food waste, recycling organic materials, and manure. The resulting mixture is rich in plant nutrients and beneficial organisms, such as bacteria, protozoa, nematodes, and fungi. Compost improves soil fertility in gardens, landscaping, horticulture, urban agriculture, and organic farming, reducing dependency on commercial chemical fertilizers. The benefits of compost include providing nutrients to crops as fertilizer, acting as a soil conditioner, increasing the humus or humic acid contents of the soil, and introducing beneficial microbes that help to suppress pathogens in the soil and reduce soil-borne diseases.
Hydroponics is a type of horticulture and a subset of hydroculture which involves growing plants, usually crops or medicinal plants, without soil, by using water-based mineral nutrient solutions in an artificial environment. Terrestrial or aquatic plants may grow freely with their roots exposed to the nutritious liquid or the roots may be mechanically supported by an inert medium such as perlite, gravel, or other substrates.
Vermicompost (vermi-compost) is the product of the decomposition process using various species of worms, usually red wigglers, white worms, and other earthworms, to create a mixture of decomposing vegetable or food waste, bedding materials, and vermicast. This process is called vermicomposting, with the rearing of worms for this purpose is called vermiculture.
Vermiculite is a hydrous phyllosilicate mineral which undergoes significant expansion when heated. Exfoliation occurs when the mineral is heated sufficiently; commercial furnaces can routinely produce this effect. Vermiculite forms by the weathering or hydrothermal alteration of biotite or phlogopite. Large commercial vermiculite mines exist in the United States, Russia, South Africa, China, and Brazil.
Coir, also called coconut fibre, is a natural fibre extracted from the outer husk of coconut, and used in products such as floor mats, doormats, brushes, and mattresses. Coir is the fibrous material found between the hard, internal shell and the outer coat of a coconut. Other uses of brown coir are in upholstery padding, sacking and horticulture. White coir, harvested from unripe coconuts, is used for making finer brushes, string, rope and fishing nets. It has the advantage of not sinking, so can be used in long lengths in deep water without the added weight dragging down boats and buoys.
A mulch is a layer of material applied to the surface of soil. Reasons for applying mulch include conservation of soil moisture, improving fertility and health of the soil, reducing weed growth, and enhancing the visual appeal of the area.
A houseplant, sometimes known as a pot plant, potted plant, or an indoor plant, is an ornamental plant that is grown indoors. As such, they are found in places like residences and offices, mainly for decorative purposes. Common houseplants are usually tropical or semi-tropical, and are often epiphytes, succulents or cacti.
A growbag is a planter filled with a growing medium and used for growing plants, usually tomatoes or other salad crops. Originally made of plastic, modern bags are also made from jute or fabric. The growing medium is usually based on a soilless organic material such as peat, coir, composted green waste, composted bark or composted wood chips, or a mixture of these. Various nutrients are added, sufficient for one season's growing, so frequently only planting and watering are required of the end-user. Planting is undertaken by first laying the bag flat on the floor or bench of the growing area, then cutting access holes in the uppermost surface, into which the plants are inserted.
A soil conditioner is a product which is added to soil to improve the soil’s physical qualities, usually its fertility and sometimes its mechanics. In general usage, the term "soil conditioner" is often thought of as a subset of the category soil amendments, which more often is understood to include a wide range of fertilizers and non-organic materials. In the context of construction soil conditioning is also called soil stabilization.
Passive hydroponics, semi-hydroponics or passive subirrigation is a method of growing plants without soil, peat moss, or bark.
This is an alphabetical index of articles related to gardening.
Agricultural soil science is a branch of soil science that deals with the study of edaphic conditions as they relate to the production of food and fiber. In this context, it is also a constituent of the field of agronomy and is thus also described as soil agronomy.
Ebb and flow hydroponics is a form of hydroponics that is known for its simplicity, reliability of operation and low initial investment cost. Pots are filled with an inert medium which does not function like soil or contribute nutrition to the plants but which anchors the roots and functions as a temporary reserve of water and solvent mineral nutrients. The hydroponic solution alternately floods the system and is allowed to ebb away.
Lightweight expanded clay aggregate (LECA) or expanded clay (exclay) is a lightweight aggregate made by heating clay to around 1,200 °C (2,190 °F) in a rotary kiln. The heating process causes gases trapped in the clay to expand, forming thousands of small bubbles and giving the material a porous structure. LECA has an approximately round or oblong shape due to circular movement in the kiln and is available in different sizes and densities. LECA is used to make lightweight concrete products and other uses.
Dendrobium loddigesii is a miniature to small sized, warm to cold growing epiphyte, lithophyte or terrestrial orchid that comes from Laos, Vietnam, and China. It is found in humid, mossy, mixed and coniferous forests at elevations of 1000 to 1500 meters, in areas with dry winter and a wet spring and summer. The plant has tufted, pendant, subterete, striated, several-noded, white-sheathed stems carrying alternate, fleshy, oblong, acute leaves.
Many types of flowering plants are available to plant in flower gardens or flower beds. The floral industry calls these plants, bedding plants. These fast-growing plants in seasonal flower beds create colourful displays, during spring, summer, fall or winter, depending on the climate. Plants used for bedding are generally annuals, but biennials, tender perennials, and succulents are used.
Dracaena pinguicula, synonym Sansevieria pinguicula, also known as the walking sansevieria, is a xerophytic CAM succulent native to the Bura area of Kenya, near Garissa. The species was described by Peter René Oscar Bally in 1943.
There are many ways to garden in restricted spaces. Often a small or limited space is an issue in growing and cultivating plants. Restricted space gardens can be located on small lawns, balconies, patios, porches, rooftops, inside the home, or in any other available place. Gardening in small places can be applied to edible or floral plants. Growing food has many benefits including saving money; healthier, fresher, and better tasting food; knowledge of pesticide and fertilizer exposure. Gardening is a good form of exercise and has been proven to be therapeutic.
Growstones are a substrate for growing plants that can be used for soilless purposes or as a soil conditioner. This substrate is made from recycled glass. It has both more air and water retention space than perlite and peat. Another property of this medium is that it holds more water than parboiled rice hulls. Growstones appear to be a comparable alternative to expanded clay aggregate.
Dracaena eilensis, synonym Sansevieria eilensis, is a species of succulent plant native to a small region of Somalia near the town of Eyl. The species was collected in 1973 by John Lavranos.
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