What is The Kratky Method?
It's a non-circulating hydroponics approach that requires no moving parts and very little effort. Plant roots need oxygen, which they usually get from the soil and the water or air flowing through it. If they sit in stagnant water they can suffocate. By allowing the water level to drop as the roots grow down, you allow them to get oxygen from the moist air in the container.
The Kratky Method can be used to grow almost anything but it's best suited to greens and herbs, such as lettuce or mint. The Kratky Jar in particular should only be used for small plants that reach their maturity quickly.
What you need
- A large jar
- A net cup that fits the jar's opening
- Rock wool, clay pellets, or both
- Clean, pure water
- Hydroponic nutrients
- Plant Seeds
- Select a large jar with a two-inch mouth. 32-64 ounce jars are fine. The bigger the better.
- Select the seeds you want to use. We'll base these instructions on an easy one: lettuce. Feel free to experiment.
- Soak your growing medium (rock wool or clay pellets) in clean water
- Arrange the pre-soaked rock wool and clay pellets in your net cup.
- Carefully place 2-3 seeds (more doesn't hurt) in the rock wool.
- Fill the jar with pure, clean water until the bottom half inch of rock wool is submerged
- Wait for the sprouts to emerge. Don't follow the next steps until you see a tap root growing into the water.
Transitioning to growth
- Once you see a small tap root descend into the water, prepare a nutrient solution. Follow the guidelines provided by the manufacturer or search the internet for suggestions. We may start a separate article about nutrient solutions...
- Remove the clean water from the jar and wrap the jar with foil, or block the light in a different way. Allowing light to get into the jar will result in algae, moss, fungus, bacteria, and many root problems.
- Replace the clean water with your nutrient solution. Don't fill the jar too high. The nutrient solution should not touch the net cup, but the tap root should be submerged more than 1 inch.
- Place your jar in a bright window. South-facing if you live in the Northern Hemisphere and North-Facing if you live in the Southern Hemisphere. West-facing windows can work in a pinch. It's very easy to under-estimate the amount of light needed. Put it right on the windowsill and avoid windows shaded by trees. Feel free to supplement with artificial light. We'll probably create an article soon about selecting and using artificial light.
As it grows
- Keep an eye on the plant and its water supply. The roots should grow down faster than the water drops, but add a little more nutrient solution if they can't reach it. Never add plain water.
- The water level will drop faster as the plant grows. It's ok to let the water get almost empty, but if it completely dries out the plant will die very fast.
- If the water runs low and the roots aren't too crowded, add more. If the roots are crowded, either harvest the plant or carefully transfer it to a larger container. We'll likely add an article explaining how to migrate your plant to a larger Kratky jar.
Once your plant outgrows its container or matures, harvest it! Some plants can be harvested periodically throughout the growth period. Most herbs and some greens respond well to periodic harvesting, while others need to be left alone until maturity.
After you've completed the cycle, it's advisable to immediately empty and clean the jar so you can use it for something else. If you let it set, it will be harder to clean, and if you put a new plant in without fully cleaning it you risk exposing the seedling to harmful pathogens.