How much should I water?

Rockwool.

A general rule for Rockwool slabs in trays is that three daily one minute feeds (50ml) should be sufficient during the first week; then six to ten (50 – 100ml) feeds per day – starting several minutes before the lamps have been turned on and two hours before they are switched off. Rockwool substrates hold liquid while still draining well, however it is still possible to over water. For optimum results regularly check the moisture content of the medium and ensure it is not water logged. Only water the plants during the day period.

Perlite.

The amount of irrigation water to apply is perhaps more important than how and when to irrigate. A general rule of thumb to follow in irrigating greenhouse crops is to apply 10 – 15% more water than the container will hold. Only water the plants during the day period.

Coconut coir pith.

A general rule is that one daily feed should be sufficient during the first few weeks; then two feeds per day – two hours after turning the lamps on and two hours before switching them off. Do not water the plants too often or give too much water. By reducing the watering frequency, optimal water replenishment is established. This improves the capacity of the coconut substrate to absorb all the nutrients, optimises the drainage and air in the medium and prevents accumulation of salts within the coconut substrate. If the EC of the irrigation water is higher than 0.6 mS/cm, then it is better to increase the water dosage until drainage of 20% has been reached (1/5 of the irrigation solution has to leave the medium again). If the EC of the irrigation water is lower than 0.6 mS/cm, a lower drainage of 10% will suffice. Reiziger Coconut Coir Pith holds liquid while still draining well, however it is still possible to over water. When growing in cocoponics, determining pH and EC from drainage water is not a true indication of the coconut substrates value. For optimal results, you are encouraged to use the 1: 1.5 extraction methods.

Expanded Clay.

A general rule of thumb to follow in irrigating greenhouse crops is to apply 10 – 15% more water than the container will hold. Frequency of application will depend upon plant size and greenhouse temperature, but will vary from one 15 minute feed every hour while the lights are on during the first weeks of growth; then one 15 minute feed every two hours – starting several minutes before the lamps have been turned on. Only water the plants during the day period.

Recirculating systems.

Compared with cultivating on substrates with high nutrient and water buffers, such as coconut coir substrates, recirculating systems require closer monitoring of the feed and the plants because they contain insufficient nutrient buffer which means changes to the nutrient solution have a direct and sudden impact on the plant. The feed reservoir must contain at least 5L per plant. The more feed there is available for the plants, the smaller any fluctuations in the pH and EC will be. Under normal circumstances renew feed every 7 – 14 days. If not renewed in time the desired balance between the different nutritional elements will be severely disrupted. Between changes, the feed reservoir needs to be regularly topped up to its original level when 25 – 50% of the feeding solution has been used. It’s best to use a solution that is approximately half as strong as the original feed solution. In circumstances where evaporation is a concern, the reservoir is best topped up with tap water e.g. high temperatures and low humidity. This way evaporation can take place easily while the nutrient solution’s EC is prevented from rising.