The Kratky method is a very interesting type of hydroponics that allows you to grow plants with minimal effort and very cheaply. However, if you choose this type you will still need to pay some attention to it.
QUICK ANSWER: The Kratky method was originally designed as a hydroponic system that does not require water changes. However, the practice has shown that you do need to change the water regularly.
As the plants grow, they extract the nutrients they need from the nutrient solution. But at the same time, a lot of calcium and magnesium remain in the solution. This leads to an imbalance of elements and a change in the pH of the water. As a result, the leaves may turn yellow or brown and curl.
In addition, stagnant water in the container is an ideal environment for the development of bacteria and fungi. If disease pathogens get into the solution, it will lead to root rot.
Changing the water will solve all these problems that are sure to arise during cultivation in the Kratky system.
How often do you change the water in Kratky?
The frequency of water changes in Kratky depends on what size container you are using and what kind of plant you are growing.
For example, if you are growing a single lettuce bush in a one-gallon container, you won’t need to change the water very often. On the other hand, if you have a big bush of regular tomatoes in that container, you should do a water change about twice a month.
All in all, we can say that you should change the water at least once a month in any case. The best indicator that the water needs to be changed is the pH and the EC of the water. You should check them at least once a week.
The pH and EC will be different for each culture, so I will leave below a table where you can find the values you need.
| Plant | Optimal pH | Optimal EC |
|---|---|---|
| Artichoke | 6.5-7.5 | 0.8-1.8 |
| Arugula | 6.0-7.5 | 0.8-1.2 |
| Asparagus | 6.0-6.8 | 1.4-1.8 |
| Basil | 5.5-6.5 | 1.0-1.6 |
| Bean (Common) | 6.0 | 2.0-4.0 |
| Beetroot | 6.0-6.5 | 0.8-5.0 |
| Bok Choi | 6.0-7.0 | 1.5-2.5 |
| Broad Bean | 6.0-6.5 | 1.8-2.2 |
| Broccoli | 6.0-6.5 | 2.8-3.5 |
| Brussell Sprout | 6.5-7.5 | 2.5-3.0 |
| Cabbage | 6.5-7.0 | 2.5-3.0 |
| Capiscum | 6.0-6.5 | 1.8-2.2 |
| Carrots | 6.3 | 1.6-2.0 |
| Cauliflower | 6.0-7.0 | 0.5-2.0 |
| Celery | 6.5 | 1.8-2.4 |
| Cucumber | 5.5-6.0 | 1.7-2.5 |
| Eggplant | 5.5-6.5 | 2.5-3.5 |
| Endive | 5.5 | 2.0-2.4 |
| Fodder | 6.0 | 1.8-2.0 |
| Garlic | 6.0 | 1.4-1.8 |
| Kale | 5.5-6.5 | 1.2-1.5 |
| Leek | 6.5-7.0 | 1.4-1.8 |
| Lettuce | 5.5-6.5 | 0.8-1.2 |
| Marrow | 6.0 | 1.8-2.4 |
| Okra | 6.5 | 2.0-2.4 |
| Onions | 6.0-6.7 | 1.4-1.8 |
| Pak Choi | 7.0 | 1.5-2.0 |
| Parsnip | 6.0 | 1.4-1.8 |
| Pea | 6.0-7.0 | 0.8-1.8 |
| Pea (Sugar) | 6.0-7.0 | 0.8-1.8 |
| Pepino | 6.0-6.5 | 2.0-5.0 |
| Peppers | 5.8-6.3 | 2.0-3.0 |
| Peppers (Bell) | 6.0-6.5 | 2.0-3.0 |
| Peppers (Hot) | 5.0-6.5 | 3.0-3.5 |
| Potato | 5.0-6.0 | 2.0-2.5 |
| Pumpkin | 5.5-7.5 | 1.8-2.4 |
| Radish | 6.0-7.0 | 1.6-2.2 |
| Spinach | 6.0-7.0 | 1.8-2.3 |
| Silverbeet | 6.0-7.0 | 1.8-2.3 |
| Sweet Corn | 6.0 | 1.6-2.4 |
| Sweet Potato | 5.5-6.0 | 2.0-2.5 |
| Taro | 5.0-5.5 | 2.5-3.0 |
| Tomato | 5.5-6.3 | 1.5-3.0 |
| Turnip | 6.0-6.5 | 1.8-2.4 |
| Zucchini | 6.0 | 1.8-2.4 |
Read also: How to choose a hydroponic system?
How to change the water in the Kratky system?
To properly change the water in the Kratky you need to pour fresh water so as not to drown the air roots.
In the Kratky system, plants develop a root system as the water in the container decreases. The lower the water level gets, the longer the roots get.
However, over time, the upper part of the roots will become air roots. In other words, this type of root starts to absorb oxygen instead of water. Such roots are usually placed closer to the lid and have the appearance of white fuzz mixed with filamentous roots.
Clean up your Kratky
First, you need to clean your system. If you pour water into a dirty container, the effect of replacing it will be incomplete.
Pull the plant and the pot out carefully and put it in another container with water. Then use a plastic brush and scrape off all the dirt from the inside of the container and the lid. After that, rinse all parts under running water.
Pour a full container of water and add 5 milliliters of 35% hydrogen peroxide to each gallon. Leave everything as is for 30 minutes. Then drain the water and rinse the container again.
Water
You need to use the right water to be successful. The best water for any hydroponic system, including Kratky, is distilled water.
This type of water is good because it does not contain any microorganisms. As a result, the solution based on this water will stay cleaner for a longer period of time.
A good alternative is regular tap water. It is much cheaper but needs to be pre-treated. Before filling your Kratky with tap water, run it through the UV sterilizer.
Water pH
One of the reasons to replace the water is the pH of the water. It slowly changes over time and the water becomes unsuitable for hydroponics.
Check the pH of the fresh water before putting the plant in place. To do this, use a special device that can determine both the pH and the EC of the water. If you don’t have one, you can buy it inexpensively at a hydroponic store or online.
For most plants, a pH of 5.5-6.0 is normal. But it is best if you use the chart above to determine the exact pH for your plant.
To lower or raise the pH you can use the right ingredients that are available at any hydroponic store.
Nutrients
The last thing you have to do is add fertilizer so that the water turns into a nutrient solution. Use the same nutrients as before because the plants are already used to them.
Use the chart above to see what EC your plant needs. Use the measuring device I mentioned in the previous chapter to determine the EC.
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Very helpful
I tried hydroponics last year with some success using 2 or 3 different methods. With the deep water culture -5 gallon Pails with air induced – Grew well up to producing the large cukes, and then leaves started to dry up . Added water as needed with nutrient , but did not change out water completely. Also tried the circulating NFT (or whatever it is called) in a 108 hole smaller system . Lettuce, pak choi grew fine, but tomatoes and peppers never matured to any extent. Also tried the Kratky method in smaller 4 or 5 gallon buckets in baskets with pellets, also same thing with aeration for melons but nothing matured in house or greenhouse.Had some success with tomaoes in kratky water about 4 inches deep in greenhouse, but no pepers matured. Added water and nutrient when level dropped – but did not fill to the level you show in the line of root color. I had never read anywhere before about changing water after a certain period.
Trying Aerogarden this year with germuination plate and it seems to be working better than the Jiffy pellets.
I had the best luck in the ground with loads of cukes and melons. Will try using your recommendations with hydroponics this year if I can print off a copy of your letter.