Algae is a green film, slime or cloudiness in the nutrient solution, often coating the container walls or the roots. It needs just two things to grow: nutrients and light. A Kratky container always has the nutrients, so the light is the part you control.
Why Algae Is a Problem
- It competes for oxygen, especially at night, which stresses roots that already rely on the air gap.
- It uses nutrients meant for the tomato.
- It coats roots and can make it harder to tell healthy white roots from rotting ones.
- Dying algae decays in the solution, which can feed the water molds behind root rot.
A little algae won't kill a tomato, but it is a sign that light is getting in, and that is easy to fix.
How to Stop It
- Block the light. Use an opaque container, or wrap a clear jar or tote in foil, a sleeve or dark tape. See Kratky tomato container size.
- Cover every gap in the lid. Fill around the net cup with clay pebbles and cover spare holes.
- Keep the growing medium's surface dry and dark. A layer of clay pebbles on top stops algae growing on wet rockwool.
- Don't wipe the roots. Leave them alone; removing light stops new growth.
- Clean between crops. Scrub and rinse the container and net cups before reusing them.
If algae is heavy and the solution smells bad, replace it with a fresh mix in a clean, dark container, set at the water roots' level.
Back to Kratky tomato problems.
Frequently Asked Questions
Why is there algae in my Kratky container?
Because light is reaching the nutrient solution. Algae needs light and nutrients, and the solution always has nutrients.
Is algae harmful to Kratky tomatoes?
A little isn't, but heavy algae competes for oxygen and nutrients and can encourage root rot.
Can you use a clear mason jar for Kratky tomatoes?
Yes, if you cover it. Wrap the jar so no light reaches the solution, and leave a narrow strip you can uncover to check the water level.