When my wife and I first got into hydroponic growing, we didn’t know what to expect.
We’d heard how it was easier, saved on space, reduced mess from the soil, and helped plants grow faster, but we were skeptical.
Wow! Hydroponics really live up to the hype.
As we’ve experimented with different methods, one of them I’d heard about that intrigued me was the Kratky method and the Kratky jar.
A Kratky Jar is a single container where you keep the plant and the hydroponic solution. Sometimes called mason jar hydroponics, you put your plant in a growing medium and suspend the roots from the top of the container into the nutrient-rich water, leaving a 1/4-1/2″ inch gap of air for oxygenation.
Look ahead for more details and quick setup instructions.
Table of Contents
What Is The Kratky Method?
At its core, the Kratky Method is a non-circulating hydroponics system.
Most other hydroponics work best when there is an air pump and a water pump.
The water pump keeps the water moving and circulating through the roots, allowing for better nutrition of the plant.
An air pump adds oxygen back into the water for better oxygenation at the roots.
However, these extra parts require more setup and a higher cost upfront.
The Kratky Method provides a compromise for oxygenating the plant without needing these extra parts.
The plant’s roots dangle into a non-moving hydroponic solution. While the container is often a mason jar, it doesn’t have to be.
The level of the solution is almost all of the way up to the root crown. Kratky leaves a 1/4-1/2″ inch gap of air between the root crown and the water.
As the roots get longer, stick more to the 1/2″ inch mark. A little longer is OK when the plant is well-established.
The roots exposed to the air develop openings with which they draw in oxygen.
The lower parts of the roots continue to pull up water and nutrients.
When the water dips below what the roots can reach, you refill the water back to the same gap.
What Is A Kratky Jar?
A Kratky Jar is a Kratky system that specifically uses a glass jar, often a mason jar.
This is the most common use of the Kratky method and works well with smaller plants and herbs.
Keep in mind: if the roots start to press against the edges of the container, they’ll become root-bound and not absorb as many nutrients.
It’s possible to fix this with root pruning or root trimming, but if you want to avoid the issue altogether, pick a smaller plant.
You may want to check out our guide to root trimming in hydroponics.
Small plants and herbs that work well with Kratky Jars are:
- Lettuce
- Spinach
- Cilantro
- Parsley
- Cabbage
- Cherry Tomatoes
- Rosemary
- Basil
- Catnip
- Chives
- Mint
- Beans
How To Set Up A Kratky Jar
Setting up a Kratky Jar is pretty simple.
Here’s what you’ll need:
- Mason jar
- Net pot
- Seeds
- Rockwool cubes*
- Hydroponic solution
- Grow light or sunlight
- Clay pebbles
*If you don’t want to use Rockwool, that’s fine. Check out our list of Rockwool alternatives in hydroponics.
First, sprout your seeds in the Rockwool cubes using the hydroponic solution and cover the cubes until they sprout.
Then, fill your jar with the hydroponic solution according to the directions on the specific product package.
Put your seedling and Rockwool in the net pot and fill around it with the clay pebbles.
Put the net pot in the jar and check the water levels, making sure to leave a slight air gap between the root crown and the water.
Put the plants under the grow lights or in the sun.
When the water dips below the roots (or when it gets close), fill it up with distilled water, but don’t add any more nutrients.
When you’ve filled half the jar or replaced half the water, dump the water out and start fresh with a new hydroponic mixture.
Repeat until the plant is grown.
This is, of course, a brief rundown on how to set it up.
For more details, check out our guide to mason jar hydroponics and how to set it up.
What To Watch Out For In The Kratky Method
The Kratky method is easy, but it isn’t perfect.
The biggest issues come in these areas, and I’ll offer some advice on how to adjust for them.
Higher Chance Of Mold And Algae
When water is warm and packed with nutrients, bacteria thrive.
Hydroponic reservoirs and tanks are breeding grounds for mold and algae in general, but this is usually fixed by keeping the water moving due to water pumps and air pumps.
Kratky method systems don’t have this, so the stagnant water gets gross pretty quick if you’re not careful.
There’s no good way to avoid this other than checking on the water often.
When you see buildup or whenever you change the water, give the jar a quick rinse and wipe to remove any buildup.
Also, take the extra care you never accidentally get any debris in the water during the refilling process.
Oversaturation Of Nutrients
One of the most common (and yet easily avoided) mistakes with the Kratky method is nutrient oversaturation.
Most people get the hydroponic solution mixture right.
It’s pretty easy, after all; all you do is follow the directions on your specific mixture.
Where the problem happens is when you need to add more.
It might make sense to add more nutrient-rich water, but you don’t want to do this.
Add in regular water, so you don’t create pockets of supernutrition, which could clog the roots and prevent nutrition altogether.
Once you’ve replaced half the water, dump out the water and put in a whole new set of hydroponic water.
Poor Oxygenation
Air pumps are critical for reoxygenating the water. Plants draw a lot of oxygen out, more than you’d think.
Kratky helped offset this by making sure there’s an air gap, as we’ve discussed before.
Don’t let those upper roots get submerged. We want to encourage them to develop the right oxygen receptors to make up the difference.