Keep light away from the nutrient solution. Algae needs light to grow, so a fully covered jar won’t grow it. Wrap or paint the jar and make sure the net cup and lid leave no gaps.
Why Algae Is a Problem
Algae competes with your plant for nutrients, can coat the roots and makes the solution smell. A little green on the outside of the net cup is harmless; a jar full of green water is not.
Ways to Cover a Jar
- Sleeves: a sock, a fabric sleeve or a cut-down cardboard tube slides on and off, so you can still check the roots.
- Paint or tape: spray paint or opaque tape blocks light for good. Leave a thin vertical strip you can cover with a flap if you want to see the water level.
- Foil: quick and cheap, though it tears easily.
Don’t forget the top: light getting in around a loose net cup is enough to start algae.
If Algae Has Already Started
Cover the jar right away; without light, the algae stops spreading. If the solution is badly fouled and the plant is young, move the plant to a clean, covered jar with fresh solution.
Between Crops
Wash jars with hot soapy water and rinse well before reusing them, so you don’t carry algae into the next crop.
We grow in mason jars indoors all year, and covering the jars is the single habit that matters most.
Related guide: growing Kratky on a kitchen windowsill.
