Types of Medium
Most of the growing mediums available fall into two main groups. One group includes things like rockwool, perlite, sand and clay pellets. This group of mediums don`t contain any organic matter or nutrients. The second group includes things like compost or soil, they do contain organic matter and some nutrients.

Soil Based Mediums
The organic elements in composts and soil attract nutrients and water in the same way as a plants roots do. This effect is called buffering and means roots in soil based mediums don`t have all the nutrients given to them available straight away. The roots have to compete for them with the medium. Buffering stops plants roots being burnt so easily by strong nutrient solutions but it also reduces the plants ability to get at the nutrients in the first place. To counter this growers mix soil conditioners into the compost. Soil conditioners are just other non-organic (low-buffering) mediums like perlite or sand.

A Basic Potting Mix
A blend of 50% non-peat based potting compost and 50% perlite is a good basic mix to start growing with in pots. Before filling the pot add a layer of pure perlite or washed gravel a few cm`s deep to help with drainage. Gradually increase the size of the pot as the plant grows rather than jumping straight to a large one. This will help ensure even root distribution throughout the pot.

Soil From Your Garden
Soil from your garden can contains pests and diseases so don`t use it unless you are actually growing in the ground outside. Even then you will need to improve it with soil conditioners to get good results. Most growers simply dig a hole and fill it with a fresh blend of compost and growing mediums rather than running the risk of using the local soil.

Mixing Mediums and Nutrients
Cannabis uses available nutrients very quickly so mixing in nutrients or fertilisers with the growing medium can be a bit of an art. It`s easier to leave the mixture plain and give plants nutrients in their water as and when they require them.

Hydroponic Mediums

Rockwool
Rockwool is a common medium used for hydroponics but does have some drawbacks. Just like the loft insulation variety when dry it`s very dangerous to handle. Most also has a high p.h. value. This can be reduced initially by soaking in hot 5.5 p.h water for at least 24 hours before use. Pre used rockwool can be sterilised by baking in a hot oven for a couple of hours.

Clay Pellets (HEC)
Hardened expanded clay or clay pellets are a good reusable medium that can be used in pots. These little marble sized balls absorb loads and loads of water and release it slowly. Good for hydroponics and safer than rockwool but they are prone to dry spots when drip fed. Wash through with a 10% bleach 90% water solution after each crop to neutralise nutrient build up.

Nutrient Film Technique
N.F.T produces excellent results using small cubes of rockwool, or small pots of perlite placed on a thin mat that is drip fed a nutrient solution. The plant roots grow out the cubes or pots and weave through the wet matting. This technique can be very economical with the growing medium yet still support very large plants.

Cover Your Medium
Whatever medium you choose cover it with a light tight material if possible to stop algae growth competing for the nutrients. This will also help to keep the area around the roots moist. An inch layer of pure perlite on top of pots or white plastic sheeting will also help reflect light back up to the plants.

Flushing
Over time excess nutrients and salts build up in growing mediums making them more and more toxic to the roots. Plants grown in pots suffer from this very quickly if they are watered using drip trays that don`t allow excess water to drain away. One way to counter this build up is to flush the growing medium once a month with warm p.h balanced water. Use water to about 3 times the volume of the medium and keep pouring it through while allowing the excess to drain away. You can test the run off water if you like until it gets to acceptable levels. If the plants are in pots finish flushing with a 1/4 strength nutrient feed and then continue feeding patterns as normal.