As one of my professors always said:
There is no perfect substrate, but a perfect management for each substrate.
Many materials can potentially be used as horticultural substrates. There are some quite exotic like rice hull, volcanic rock, coco dust, biochar… In fact the ideal substrate for you is the most accessible, cheap, that covers your needs and you can manage.
You can find a lot of different substrates and pre-formulated mixtures which are available for sale. In order to choose the right one it is advisable to know how each of them behaves: how much water they retain, if they contain nutrients or not, durability, cost… Here you are the most common substrates with a brief description of their pros and cons.
- It is totally inert (it is easier to balance of the nutrient solution)
- Good capacity of aeration.
- Good water retention.
- It does not decay easily, so it can be used 5-6 times.
On the other hand:
- Its manufacturing uses a lot of energy (not very ecological)
- Its waste is a pollutant.
- Last but not least, it is expensive.
It has similar characteristics to rock wool. You will find different granulometries (grain size); the thickest is used to mix with denser substrata to improve aeration. Thinner perlites serve as a good hydroponics substrate without mixing.
- Totally inert
- Good aeration and water retention.
- It adapts easily to any container.
- It is reusable up to 5-6 times (after disinfection)
- It is not degradable, like rock wool, and causes the same environmental problems.
Coco peat (also coco coir)
- It retains a lot of water. It is the best substrate to be using when there is a blackout because your plants will survive for a few days without watering (if it is not also too hot).
- It has very good aeration. Being difficult to flood means that you will not asphyxiate the roots with too much watering.
- It contains enough phosphorus (P) and potassium (K) so you should use a specific nutrient solution for coco with less of these nutrients.
- The particles are small. If you re-circulate the water you need to put a filter on the pump intake or else the dirt could obstruct it.
- It degrades with time. Do not use it for more than three cycles as it is decomposing and compacting, losing its qualities.
Expanded clay (or arlite)
- Totally inert.
- Great aeration.
- Very low water retention: it needs frequent watering.
- Remember to stabilize the pH before using it (it is too high and we must lower or acidify it)
- It is easy to clean, can be reused almost eternally. It is perfect for the eco-conscious.
Sand is the infinite substrate: due to his extraordinary mechanical resistance it last practically forever. Be careful with sand that is not specifically sold as a substrate because its characteristics (pH, granulometry) could be inappropriate for growing.
- Easy to disinfect and reuse.
- Good capacity of aeration and drainage (using a proper grain size)
- Water retention is low. It needs to be watered frequently, especially if environment temperature is high.
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