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.
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 |
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 roots 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.
It is important that you do not submerge the aerial roots in water. In the photo, you can see which roots are regular and which are air roots.
Determine where the aerial roots of your plant are and fill the container with fresh water 1 inch below that level.
Clean up your Kratky
Even though I wrote at the beginning of this chapter how to properly pour water into your Kratky you first 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. It is important to do this so the plant does not dry out while you are cleaning your Kratky.
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.
The disadvantage of distilled water for hydroponics is the price. If you have a large Kratky system, you will have to spend a lot of money on distilled water to fill it completely.
A good alternative is regular tap water. It is much cheaper but needs to be pre-treated.
Install a UV sterilizer in your water system. The fact is that the chlorine used to purify tap water does not kill all the microorganisms that are in it. Therefore, before filling your Kratky with 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.