Choosing the right growth media can seem confusing at a glance because there are so many to choose from. Some hydroponic systems will work with any growth media choice, however some are more specific. Getting everything right when growing indoors can be a bit of a learning curve, but we want to make things just a little bit easier.
So What is Growth Media?
Growth Media is simply anything that will hold a plant’s root structure so it can grow, right from the seedling/cutting through to adulthood. In hydroponics, various different growth mediums are used within different applications. Ever grow cress in cotton wool at school? It’s just like that.
The growth media is needed to help plants to establish their root structure - vital to getting a healthy plant.
Different growth mediums come with different benefits, and choosing the right one depends on the plant's needs and the system being used.
Some mediums already contain essential nutrients and minerals, reducing the need for additives. Others are completely inert, thus they have no nutritional value. With these ones, you do need to add the nutrients and additives but this gives you more control over what your plant is getting.
Basic Growth Media
When deciding on which growth media to use, it helps to know the characteristics of each one and whether it will work in the hydroponics system you're using. Here's a list of the main growth media mixes that you'll come across.
Various soil mixes exist within hydroponics, each giving a different benefit. Some are pre-fertilised so that minimal additives and supplements are needed, whilst some contain very little nutrition to allow you greater control.
You’ll find quite often that soil mixes contain other ingredients, depending on what their main purpose is for. These include things like sphagnum peat moss, worm castings, bone meal, beneficial microbes, lime and bat guano - all helping in a mixture of different ways. The positives range from helping with water-holding capacity, working as a natural fertiliser, helping with structure, managing the pH and preventing disease.
COCO FIBRE / COCO COIR
Coco is made from the outer husk of coconut shell. As it is naturally rich in potassium and sodium, most coco products are pre-treated by the manufacturers to make them ready to use. It is a good idea to check whether coco has been pH buffered and washed when you purchase it. Some kinds may need to be flushed a couple of times with water at pH 6.0 before plants can be put in it.
Coco is a light medium that has good water retention without becoming too soggy – it is much harder to over-water compared to soil. The air capacity is at around 30% which helps with root growth and nutrient uptake. There is also the added bonus of coco containing a naturally occurring fungus called Trichoderma that helps to prevent disease and aids root development.
Coco coir comes in a few different forms, including coco blockz, bricks and loose mixes.
Baked clay pebbles are suitable for hydroponic systems in which nutrients are carefully controlled in a water solution. The clay pebbles are inert, pH neutral and do not contain any nutrient valuable.
Clay pebbles are ecologically sustainable and re-usable thanks to its ability to be cleaned and sterilised.
COCO & CLAY MIXES
Coco & Clay Pebble mixes are ideal for Flood & Drain and other pot based hydroponic systems. Greater water retention is given compared to using clay pebbles alone, and the frequency of feeding is also reduced.
Rockwool is an inert medium, and so is completely free of nutrients. It is usually available in a pH balanced form, though this can differ between brands so it is worth checking first.
You can find rockwool in a variety of different forms including: propagation cubes, shredded mixes, horizontal or vertical slabs and blocks. The one you choose depends on what you need it for.
These mediums are similar in that they are made from porous rock material and this gives them excellent water retention qualities. They can be used on their own, or can be mixed in with soil or coco to give better water retention and air capacity to those mixes. If used alone, these growth mediums require added nutrients.
Vermiculite is a mined mineral that must be handled gently to avoid it losing porosity. As well as helping with the water-holding capacity, vermiculite adds calcium and magnesium into the mix.
Perlite is a lightweight volcanic rock, and it comes completely sterile and pH neutral. It will help to improve water drainage and increase airflow. Be careful to not add too much though or it will float during waterings!