What is a growing medium?
A growing medium is simply what your plants grow in. Soil, water, and moss are all considered to be growing mediums, amongst many others.
What is a soilless growing medium and what are the different kinds?
A soilless growing medium is just what it sounds like, something to grow plants in that isn’t soil! The most common types of growing mediums are coconut coir, clay pellets, perlite, vermiculite, peat moss, and rock wool. We will be going over the properties of each growing medium so you can decide what best fits yours and your plants needs.
Remember to always recycle your growing medium after use!
How to choose a soilless growing medium?
Since the dawn of agriculture, farmers and growers have obsessed with what their plants are growing in. While there’s something to be said for growing your plants symbiotically with other creatures in a richblack soil, having your soil achieve that zen like state can take years to achieve and most of us don’t have the time or patience to do this.
The growing medium is used as a source of water, a place to anchor itself to, and a source of nutrients for the plant. When growing in traditional soil systems, the medium can provide most of the nutrition. Additional fertilizer can be added to it, either as organic or synthetic.
The growing medium supplies the plant with nutrition!
There is typically a nutritional value in naturally occurring soil and potting soil and so maintaining proper dosages of fertilizers can be challenging. The advantage of a soilless medium is it is a clean slate when it comes to nutrients. Because of this, the grower can add whatever nutrients at whatever concentration they want and not have to worry about overdosing.
There are a number of factors to consider when deciding which type of media works the best in a particular situation including cost, drainage, and potential aeration of the roots.
Types of Soilless Growing Mediums:
Coconut coir, commonly referred to as coco, is a byproduct of the coconut industry. It is the husk of the seed which has been ground up and because of this, is essentially pure plant fiber. It is capable of holding lots of moisture, and while aeration can be okay, one should be careful not to over water as the aeration levels will quickly decrease.
Depending on location it can be relatively cheap and is probably the most environmentally sustainable type of growing medium.
In the past, the first generation of coco had sea water contamination which brought up the salinity and restricted how fertilizers could be used. Now however, this has been remedied and shouldn’t be of concern.
Coconut coir is also used to make ropes, doormats, and brushes!
Clay pellets are spherical in shape and around 2 cm(1 inch) in diameter. They are used in water culture as they offer excellent aeration due to the large particle size. Most of the time only small amounts are used, just enough to keep the plants anchored. Because they have essentially zero water retention, nutrient solution has to continually flow over the roots while using this media.
While clay pellets can be more expensive on a volume basis, only a small amount is needed which makes their pricing competitive.
It is recommended clay pellets be used on the bottom of pots containing coco or peat based media. This will give a space for drainage to occur as well as give more surface area for roots to take oxygen from.
Perlite is a mineral that has been expanded due to heat. It is extremely light and porous and can be a bit inconvenient to use as it floats on water. It is seldom used alone, but it will add aeration to heavier blends.
Similar to perlite, only heavier. It is better at holding water compared to perlite but it will hold less air.
Vermiculite will hold moisture longer than perlite!
Peat moss, otherwise known as sphagnum, is commonly used in the indoor gardening industry in Canada but is less common elsewhere. It is used in Canada more often as it is a common resource and due to its bulky nature shipping can be expensive!
The moss comes from bogs and upon its death doesn’t immediately decompose, allowing it to be harvested. It’s similar to coconut husk as it is a fibrous material; however, it has more contaminants similar to small roots from trees.
Once peat moss is dry it’s very hard to rehydrate and can have aeration and pH issues. For this reason, it is almost always used in blends, usually with perlite and vermiculite along with a pH buffer.
Rock wool, like perlite and vermiculite, is a mineral that has been modified into a growing medium. However, instead of the particles being expanded by heat, it changes into long fibers and is related to fiberglass insulation used in homes!
The advantage it has over other mediums, for example clay pellets, is that rock wool comes in performed cubes and so it is not necessary to have a pot to contain it. Simply put the plant into the piece of rock wool and connect it to an irrigation source!
Rock wool can also be called mineral wool or stone wool.
Rock wool is a key component in a new hydroponic system known as ‘drain to waste’. In traditional water culture systems, the nutrient solution is constantly being recycled. The solution goes from the reservoir to the plant and then drains back into the reservoir. A drain to waste system, on the other hand, does not recycle. Instead, the solution is fed in short bursts and is discarded afterwards. The big advantage to using this system is that a recirculating nutrient solution will warm up over time, but a drain to waste system will not which results in lower root temperatures. In a recirculating system, if a rootborn pathogen infects one plant it can be transported everything; however, in a drain to waste system any pests, spores, bacteria, or viruses will likely be flushed out. This greatly minimizes plant to plant infections.
When growing high end crops it is highly recommended to use a combination of the previously mentioned growing mediums. There are others which many modern growers would find unconventional, but in some situations may be considered. Some examples include saw dust, straw, and sand. Because of their low price they may be utilized in certain situations. Straw and sawdust hold water quite well but could harbour pathogens. Sand on the other hand, has poor water retention so would have to be closely monitored so any plants growing in it didn’t dry out.
Recycling Growing Mediums
It is everyone’s responsibility to keep as much out of the landfill as possible; however, with that being said, using the same growing medium for multiple crops can carry large risks. Fertilizers build up over time and increase the salinity, and any rootborn pathogens can be passed from crop to crop. The best and greenest option for many of these types of mediums is to use them one time in an indoor grow and then to spread the material on lawns or gardens as soil builders. If you don’t have a lawn or garden there are plenty of people who would happily take if off your hands for free! Just be sure to note if you live in an area with a prohibition as you will have to take out the root stock and dispose of it separately.
Most growers only use their growing medium once so as to prevent contamination between crops.
We hope that gave you some insight into which growing mediums may work best for you. Of course every type of grower, and plant, will work best with a medium specific to their needs. Do your research and find what will work the best for you!
Good luck! And remember you can always reach out to @futureharvestdevelopments on instagram if you have any questions or need advice.