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Watering Strategies for Rockwool Cubes and Small Containers

Growing in rockwool cubes or 1 gallon pots can produce large healthy plants with the right watering techniques. In this article we discuss how to properly dial watering frequencies in small growing containers.

The key to growing in small substrates is knowing when to water. Big plants with small root zones will require regular feedings to maintain a proper balance of nutrients and water. To determine how often you need to water depends entirely on your runoff values.

If you are unsure about how to properly collect runoff, please read the article here.  Every watering in a small or large container should always be to runoff. This runoff is collected and compared to the EC / PPM of the nutrient solution you are feeding.

The goal in small root zones is to keep the runoff EC / PPM to a maximum of a 20% rise. As an example, if you are feeding 2.0 EC (1000 PPM), the highest runoff we want is 2.4-2.5 EC (1200-1250 PPM). If the runoff is higher than 2.5 EC (1250 PPM) you must add another watering to your irrigation schedule.

So the game plan with small substrates is maintaining a proper EC / PPM level in the root zone. We achieve this by monitoring runoff and watering whenever the concentration is higher than 20% of the input. Keep the nutrient solution at full strength for every feeding. If your runoff is still too high, you need to push more feed through the root zone and drive the EC / PPM down. Flushing, partial or water only feeds are never really advised when growing in small containers unless you’re in the last week of flowering.


Updated on December 10, 2019

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