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About Growing Media

There are an endless number of plants grown in pots or containers in the UK every year. Whether they are commercial growers of roses using rock wool slabs or patio growers with their own herb garden, a basic requirement for healthy plants is a growing media that can support a healthy root system. The choice of growing media varies widely, each has their own unique characteristics which when used alone or mixed with other mediums can create the perfect conditions for any type of plant.

When choosing your growing media you need to remember to provide sufficient anchorage for the plant you are growing, adequate water retention, appropriate drainage and ample nutrient storage as well as being pest and disease free. There are many specific growing media available, such as orchid potting mixes and cacti specific mediums, but you can also make your own at home. Following is some general information on the most common growing media which should help you to create your own ideal substrate.

Soil

When looking at soil in a gardening context, a lot of the time we are referring to a mix based on soil or peat. Soils for gardening can contain any number of components from compost to worm castings or even perlite. Gardening soils contain food sources for the plant and it is not always necessary to add food to the soil. People love to garden with soil, it is easy to water and you can find or create an individual soil for any plant species. When you see how many plants grow in the earth, and have done for millions of years, you can understand why it is the most widely used medium for growing plants.


Compost

Compost is made from decomposed organic materials, derived both from plants and animals. Although it is rare for people to use compost alone as a growing medium, it is invaluable as a soil conditioner and the perfect base to build your own medium from. For more detailed information on composting see our growing into the future page.


Grow Your Own

Coconut Coir

Coco fibre is a natural growing medium which is harvested from ripened coconuts by taking the fibrous layer between the hard internal shell and the outer coating. It has been used since the 11th century as a growing medium, but only recently, with new manufacturing technologies being able to produce a sterile material, has coco fibre use began to increase rapidly. As a growing medium it can be used as a stand alone product or mixed with any number of other mediums. The hollow structure of the fibres allow for excellent aeration, even in fully soaked conditions. Coco fibre is quickly becoming a popular, sustainable growing medium of the future with applications across many forms of gardening. Try blending it with 30% perlite and 35% compost to make your own light, fertile medium for your vegetables and herbs

Perlite

Perlite is actually a volcanic glass which has expanded under intense temperatures. It is very light due to the number of air bubbles that are held within its structure. Perlite is a popular hydroponic medium as it drains well and also can hold sufficient water in the tiny air bubbles within its structure for the plants. In the home garden perlite is also used by many people as a soil enhancer creating a more homogenous (even) planting medium.

Vermiculite

Vermiculite is a natural mineral which is quite light due its expansion under heat during formation. It is rarely used as a growing medium on its own as it can hold up to 3 times its weight in water when fully soaked. Plants function best when they have abundant oxygen in the root zone and it is quite easy to see how a medium that acts like a sponge would limit the oxygen content. Although rarely used alone, vermiculite is a popular addition to potting mixes, because of its water retention capacity. Vermiculite and coco fibre are often mixed and used in trays as a medium for button mushrooms.


Rock wool

Rock wool is very similar to the fibrous, yellow batts you see used as house insulation. The only difference being that it doesn’t have any chemicals in it like the insulation does. It is manufactured from basalt, spun into thin fibres at a temperature of over 1600oC. Rock wool is an extremely versatile growing medium, it comes formed into small cubes for propagation, as slabs for use as a full term medium, as loose floc and mini cubes which can both be used to fill pots. The arrangement of the fibres in the structure of the rock wool allow for excellent aeration in the root zone. Rock wool is extremely popular with commercial growers and is starting to be recognised in home gardens as the perfect starting point for seeds and cuttings regardless of the medium used in the later stages.

Clay pebbles

Expanded pellets of clay that are inert and pH neutral, they are used in various hydroponic systems because their size allows for maximum pore space and hence oxygen in the medium. When pebbles are used on their own in hydroponics they need to have a timed watering system to ensure the plants get watered regularly enough. As you can imagine if you pour water in the top of a pot filled with pebbles the majority of it runs straight out the bottom. For this reason the are widely used in the bottoms of manually watered or dripper fed pots to allow free drainage.