Water Wisely: Irrigation Scheduling in Soilless Culture

Irrigation management is one of the most important practices in soilless culture production. There are different methods you can use to determine the irrigation amount and frequency. In this article, I will outline some practical methods that require no special equipment.

When to water

Using these methods, you can find the right moment for irrigation by visually monitoring the moisture status of the growing media, the plant itself or both. The observation method requires experience and spending more time in the greenhouse or growroom, but getting to know your plants is very beneficial. Here are three observation methods to try.

Observation Method 1

You can use this method if your plants grow in pots, small containers or even plugs. It will work best for growing media containing peat or coco peat.

• Turn the pot over.
• Observe the development of the root system and the moisture status of the growing media.
• Irrigate when you notice that the growing media gets dried out, but not completely dry.
• Watch how the root system develops. White, healthy roots indicate good irrigation practices.

Observation Method 2

• Observe the plant throughout the day.
• Learn when water deficiency symptoms show up.
• Irrigate a few hours, or even a day before, the water deficiency symptoms are visible, depending on the growing media you have.

Observation Method 3

This method will work best if you grow your plants in pots or growing bags.

• After a good irrigation, pick up some pots and estimate their weight.
• Pick up some pots with plants that need irrigation and learn to estimate when irrigation is needed by the weight of the pots or bags.

How much to water

This method allows you to determine the amount of water that should be applied with each irrigation event.

• Irrigate in excess to saturate the growing media. Once drainage stops, weigh the container.
• After 24 hours, weigh the container again.
• The difference between the first and second measurement is the daily water amount that was absorbed by the plant.

You can use this information to plan the irrigation regimen. For example, if the weight of the container after irrigation and after leaching stops is 7.5 kg, and the weight of the container 24 hours later is 6.7 kg, then the daily water requirement for one container is 0.8 kg, or 800 ml. Adding 20% excess irrigation to allow for leaching, the required daily water amount would be 960 ml/day.

The simple methods described in this article can help you decide on the right irrigation rates and timing in soilless culture production systems.