Though soil has always been the most natural medium for growing plants, it comes with a host of problems. As garden soil is a living, breathing material, it often contains harmful bacteria and is the source of many soil-borne diseases. Battling these pests is the constant bane of every gardener. Inert soil-less mediums have the advantage here: as they are sterile, they cannot support the growth of bacterial life. It is also an ideal solution for areas with hard, compacted soil. These mediums range from inorganic matter: sand, gravel, perlite, vermiculite to organic material like wood chips, coconut husk and rice hulls.
Soil-less kitchen gardening is ideal for small contained spaces, and terrace gardens with troughs or containers and vertical growth structures. But it can also be done in larger spaces. Many commercial ventures have turned to these mediums for their obvious advantages. It is easy to control the nutrients in a soil-less sterile medium, especially as the roots have a direct access to the nutrients. When plants are given exactly what is needed for growth, (pH adjusted, balanced nutrients, sunlight and water) they will grow and perform exactly as they are genetically programmed to do, and produce superior food or flowers.
Sand, gravel: Sand is commonly used for raising seedlings, but must first be washed to remove impurities. It is best to use coarse sand as it creates air pockets that will help in aeration for the roots. Gravel has larger particles, and like sand, is good for drainage. Additionally, it can be washed and re-used repeatedly.
Perlite, vermiculite: Perlite is made from minerals that are heated till they expand and become light and porous. Vermiculite is a silicate mineral that also expands and has similar properties to perlite. They are excellent aerators and can be used in various combinations with other mediums. It can also be washed and stored for later use.
Coconut husk, chips, rice hulls: Coconut husk or cocopeat is the most favourable growing medium. It is pH neutral, holds water well and also allows good aeration. Coco chips are larger and can be used in combination with other mediums.
Parboiled rice hulls are the waste product of rice; as the hulls are cleaned and dried in the process of extracting rice, they are sterile and ideal for growing plants. Like coconut fibre, it is an entirely natural product, and preferred by gardeners who use only organic materials.
Others: Water absorbent gel, peat moss, wood chips, garden compost
These mediums are best used in combination with other materials. Most gardeners have their own recipes with varying proportions for the different stages of planting. Vermiculite, perlite, cocopeat and sand are a good mix, as they retain moisture and help aerate the roots.
A fine mix of sterile garden compost and sand is preferred by many gardeners for raising seeds. Other combinations used by gardeners are: sieved manure with peat moss, and coco husk with crushed seashells.
Fertiliser and Pest Control
Plants need three main nutrients for growth — nitrogen, phosphorus and potassium, and also, a range of micro-nutrients. Soil-less mediums are inert and must be enhanced with organic fertilisers which supply necessary nutrients. Organic matter containing these nutrients will keep your soil-less medium healthy. These are: compost, clean sieved manure, ground limestone, bone meal, leaf mould, neem cake.
Fill your containers, grow bags or gardening space with the soil-less medium of your choice; you can sow seeds or plant seedlings exactly as you would in soil. Water lightly after sowing.
At first, it is best to observe how the new medium retains water; if you find it dries out soon, make a note to adjust the combination using more organic matter in future. If the mix does not have adequate drainage, add more sand or vermiculite. As always, these observations must be made in a garden diary for future reference. Periodic application of an organic fertilising solution will ensure healthy productive plants.
One of the best aspects of soil-less mediums is that the use of pesticides is almost completely eliminated.
This is the first of a two-article series on alternative mediums for gardening.