Frequency of Flood & Drain in a Hydroponic System

Flood Cycle

• The flood cycle is when the tray or planter holding the plants is flooded. This cycle normally fills the planter nearly to the top, but stops short of covering the top of the growth medium with liquid. If the top of the medium is submerged under nutrient solution, it is likely to be covered with algae in short order, causing problems in the system and competing with the plants for nutrients.

Drain Cycle

• After the container fills with liquid, the solution drains away slowly, leaving the growth medium and the plant roots wet with nutrient-filled fluid. It is important for the liquid to drain off completely, since this is the part of the process that allows the roots to take in oxygen as well as the other necessary nutrients. Depending on the setup, the solution may drain from one tray to another, filling each in turn as it flows through the system.

Systems

• The flood and drain cycle can be either a manual or an automated process. If it is handled manually, a person must fill the container with liquid to the desired level and then allow it to drain away on its own. In an automated system, a submersible pump is set to run periodically, pumping liquid to the plants until the container fills. The pump then shuts off, and the liquid drains out. Typically, the liquid is captured in a reservoir after it drains from the plants, but sometimes it is allowed to run out onto the ground, and fresh solution is used every time.

Frequency

• The frequency of the flood and drain cycle is variable. It depends on the stage of growth of the plants, the humidity and the temperature. If the weather is hot and dry, the plants will need to be flooded more often than if it is cool and humid. Plants that have set fruit also require more frequent flooding so the fruit can receive adequate liquid. This is especially true of such vegetables as tomatoes, cucumbers and summer squash. The normal flood cycle is three to four times per day. The plant container should fill in about 10 minutes, and the liquid should be gone after approximately half an hour.