When I first got into hydroponics and the Kratky method, I was drawn to the fact you didn’t need to refill the container at all.
The idea is that the roots of the plant keep growing down as it drinks up the water.
But in practice, you may need to refill the Kratky jar if you want to keep your plants growing and give them extra life.
This sparks fear of suffocating your plants (and with good reason), but there is a way to refill a Kratky safely.
To refill a Kratky jar, clean your water of chlorine and mix up the hydroponic solution ahead of time. Then, lift the plant gently out of the jar just enough to offer a space to pour the water in. Fill up the jar, leaving a 1/2″ gap below the root crown of the plant for air.
If you refill before half of the water is gone, instead use normal water without nutrients.
Let’s get into this question a little bit more.
Table of Contents
Do You Need To Refill A Kratky Jar?
Many people don’t refill their Kratky jars at all, and I didn’t either when I first started.
One of the pains of hydroponic systems, in general, is making sure there’s always enough water.
After all, hydroponics is a soilless system, so it needs a ton of water.
The Kratky method is known for removing the need for an air pump and potentially removing the need to rewater.
All the hydroponic and nutrient-rich water is in the jar or other container from the beginning.
As the roots develop and drink more water, they keep pace with the dwindling water.
When the water is gone, harvest the plant.
In practice, you’ll find some plants drink water faster than their roots grow.
You may also find they slow down growth as the water stagnates a bit.
Or you may want to extend the life of the plant for a bigger harvest.
Whatever the reason, it’s worth it to figure out how to safely refill your system.
It’s not a necessity, but chances are, you’ll want to do this at some point.
Kratky jars aren’t the only way to use this method, but it’s the most common.
Learn more about what a Kratky jar is.
How Do You Refill A Kratky Jar?
Decide When To Refill
First, decide when to refill.
You must refill if the roots don’t reach the water. Full stop. Fill it up.
But I’m all for fresh water and helping these plants grow even faster with a lot of water.
My rule of thumb is to refill when the water is halfway down the jar or container.
Remove Chlorine From The Water
When it’s time to give your plant more water, you need to make sure the water has no chlorine or chloramine in it.
In small doses, these chemicals are used as a disinfectant, and they cause no harm to humans.
But they may hurt your plant.
Tap water treated in the city-systems will often have these in it.
Cut one lemon in half per gallon of water you use, and let the lemon sit in the water for 24 hours to remove most of the chemicals.
If you have well water, make sure you know what’s in it before using it.
Our well system has a high salt content, which is safe for us, but it messes up the plant’s ability to absorb nutrients.
We have to use distilled water for seedlings and then switch to our normal water for established plants.
Mix The Hydroponic Solution OR Decide To Use Regular Water
Now you either need to mix up the hydroponic solution according to the directions on the liquid fertilizer or use regular water.
It’s not a free choice; you need to consider two situations that dictate which option you go with.
If you refill the jar and half of the original water or more is still there, use regular, untreated water.
If less than half of the original hydroponic water is left OR you’ve already added some regular water before, use a new batch of solution.
It’s not great to mix the old solution and new solution, but if you don’t want to move the plants too much to dump the old water out, add the new solution when there’s only a little of the original left.
Gently Lift The Plant As Little As Possible
Unscrew the cap if you use one, and gently lift the plant out of the container as little as possible.
Give yourself enough gap to pour water directly into the container.
Don’t pour it through the seed pod and net pot.
Fill Up With An Air Gap
Fill the jar or container up all the way but leave a 1/2″ inch air gap below the root crown.
On grown plants, feel free to keep a 1″ inch gap.
This gap allows the upper part of the roots to pull oxygen from the air.
Now, replace the plant and screw the lid back on if it applies.
For more details on how much water to use with the Kratky method, check out the detailed answer in our article at the link.
Video On Refilling A Kratky Jar
Check out this video for another perspective on this topic.
Kratky Jar Vs. Mason Jar Hydroponics
What’s the difference between a Kratky Jar and mason jar hydroponics.
Nothing. They’re two words for the same thing.
Kratky method hydroponics don’t have to use a mason jar, but it’s the most common container.
For a full guide on setting up mason jar hydroponics, click the link (pictures and video included).
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