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Choosing the right growing medium isn't a decision to be made lightly because it will determine the success of your grow and save a lot of headaches in the long run. If you are like many first-time growers and have no idea where to start, enjoy our list of the pros and cons of growing in soil, coir, rockwool, expanded clay granules and aeroponics.
Soil
There was a time when soil was the first choice for many growers, but with more and more products hitting the market, making this a more difficult choice. You should first consider things like aeration and permeability, as these will help the overall well-being of your plants. The main role of this growing medium is boosting the development of the root system.
Most commercial soil mixes on the market consist of:
Black peat – organic matter that is heavier and less fibrous than white peat
White peat - moss with high water retention
Perlite – retains moisture but
improves drainage by aerating the soil
Vermicompost – organic fertilizer rich in nitrogen and made up of worm droppings that is especially useful during the flowering period.
We recommend soil for beginner growers because it acts as a good buffer with a more stable pH than other mediums. This gives new growers a larger margin of error and more reliable grows.
Coir
Coir is an inert substrate that is extracted from the husk of coconuts, in the form of powder or its natural form, and is perfect for hydroponics.
Growing in coir is faster thanks to its aeration capacity, which results in more vigorous root development and the presence of a specific fungi that strengthens the immune system of plants by boosting microbial life. Unfortunately, it dries out much quicker and requires more frequent watering. This grow medium is definitely for more experienced growers because being an inert medium, it requires you to constantly adjust EC and pH levels at every watering.
Rockwool
Rockwool is manufactured from volcanic rock and has a pH of about 7. Like coir, rockwool offers high aeration capacity which provides fast crop, but you must monitor the pH and EC levels of the nutrient solution for rockwood often and is recommended for growers experienced in hydroponics. The benefit of rockwool over coir is that it requires much less watering that coir, but this inert substrate requires pH adjustment before use, so you will need to leave the rocks to soak in a solution with a pH of 5.5 and an EC of 0.5-0.6 for 24 hours before sowing your seeds.
Rockwool is manufactured from volcanic rock (basalt), which is heated until liquid (around 1,600 ºC) and moulded into its final shape through mechanical processing.
With a pH of about 7, this inert substrate requires pH adjustment before use. To do so, you will need to leave the rocks to soak in a solution with a pH of 5.5 and an EC of 0.5-0.6 for 24 hours, after which you will be able to sow your seeds. The pH and EC levels of the nutrient solution for rockwool are the same as for coir and require constant monitoring as well, so we recommend this medium only to growers with some experience in hydroponics.
Just like coir, the main benefit of rockwool is its high aeration capacity, which results in faster crops. Accordingly, you will have to be as thorough as with coir when it comes to watering, ensuring a good moistening/drying balance for optimal results. And, again, you won’t have to replace the rockwool before replanting provided you wash it well after harvesting.
Clay Pebbles
Expanded clay granules dramatically reduce the length of the growing cycle thanks to their high aeration capacity, much like rockwool and coir, but does not retain any moister so is often used in partnership with those other substrates.
If you use clay pebbles, you will have to replace the water about four times to ensure proper cleaning and pH adjustment or else you can expect to face major pH and EC fluctuations.