Weekly Checks and the Air Gap
Lesson 10 of 14
A Kratky container needs very little care. A short weekly look tells you whether everything is on track, and when a container needs topping up.
What to check each week
- The level: how far the solution has dropped. Mark it on the side or note it down.
- The roots: healthy roots are white or cream. Brown, slimy roots with a bad smell are a problem (Lesson 12).
- The leaves: new growth should look firm and evenly colored.
- Light leaks and algae: green water or green film means light is getting in.
How the air gap works
As the plant drinks, the level falls and a moist air space opens between the lid and the solution (Kratky, 2009). The plant grows air roots in that space, which take in oxygen, and water roots below, which take up water and nutrients (UC ANR). This is why you do not refill a Kratky container to the top: covering the air roots with water can suffocate them.
When to top up
Small, fast crops like lettuce in a big enough container usually finish on one fill. In a small jar, or with larger plants, the solution may run low before harvest. If the lowest roots are about to lose contact with the solution:
- Mix a fresh batch at the same strength and pH.
- Add only enough to reach the lower part of the roots, well below the lid.
- Never refill all the way back to the net cup.
If you have an EC meter, check the old solution first: if it reads high, top up with plain water instead of fresh solution.
Your task for this lesson
Pick a day each week to check your container and write down the level. It takes a minute, and the notes help you size the next container.
Sources
- Kratky, B.A. (2009). Three non-circulating hydroponic methods for growing lettuce. Acta Horticulturae 843: 65–72.
- UC Master Gardeners of Orange County, UC ANR. Kratky Hydroponics: Soil-Free Growing Method.