Lettuce, or more precisely lettuce, is an annual herbaceous plant that is grown mainly for the consumption of its leaves. There are more than 2,000 varieties registered in the official European catalog of species and varieties. We have chosen to present you the red batavia lettuce.
It can be grown both outdoors and indoors, provided you have sufficient light exposure. Otherwise, it is necessary to add horticultural lighting above the crop. We therefore chose to cultivate it with the Kratky method indoors under natural light for the first 2 weeks then under a horticultural LED lamp for the end of the culture.
Principle of the Kratky method
The Kratky method is a hydroponic system invented by BA Kratky. It is passive, non-circulating and very efficient. It is enough to fill the tank once with a suitable nutrient solution to ensure the whole culture. However, despite its simplicity of use, this system must respect some important rules. Find them in our article ” What is the Kratky method?” “.
How to grow lettuces with the Kratky method indoors?
To introduce you to growing salads with the Kratky method, we used a young lettuce stalk that had germinated in a germination cube. We installed it as it is in the hydroponic system to make it as simple as possible for this experiment. You can also make your seedlings in rockwool cubes. It is a more suitable substrate for this type of hydroponics.
- bucket with lid
- a hydroponic basket
- a horticultural LED lamp
- some clay balls
- hydroponic fertilizer
- pH down or pH up
- pH meter
- a young lettuce stalk
Preparation of the nutrient solution
Lettuce is not a very greedy plant. When preparing the nutrient solution, start by adjusting the pH, it must be between 6 and 6.5, this allows it to assimilate a maximum of nutrients. Then add your fertilizers in order to have an EC between 1.2 and 1.3. It should not exceed 1.5 if you do not want to burn your plant, with an excess of fertilizer. Know that a lettuce needs about 4 to 5 L of nutrient solution for its entire culture.
Filling the reservoir and transplanting the young lettuce plant
Once the solution is ready, simply fill the system reservoir. The level should reach the bottom of the hydroponic basket. In this way, the young roots will be in contact with the nutrient solution, so the plant does not dry out.
Then, install your young seedling directly in the hydroponic basket and add a few clay balls to stabilize everything.
Finally, you can now watch the roots of your lettuce grow and invade the tank while the nutrient solution gradually decreases.
We advise you to use an opaque tank to avoid the formation of algae. In addition, the fact that the system is passive also promotes their development. We used a slightly opaque white bucket, which explains the dark deposit in the bottom of our tank, as well as a greenish coloring of our roots. However, we do not note any decline in development.
Use of a horticultural LED lamp
The use of a horticultural lamp becomes necessary, if you want to enjoy it all year round. We had chosen at the beginning to place our salad at the edge of a well exposed window. But we quickly noticed a slower growth compared to lettuces planted at the same time outdoors. From there, we came up with the idea of placing our plant under a horticultural LED lamp. Growth accelerated. In just 5 days, the salad grown with the Kratky method had completely caught up with those grown outdoors. We chose a lighting cycle (photoperiod) of 16 H day and 8 H night.
If your tank has a capacity of less than 5 L, it will probably be necessary to fill it again. It is important not to drown the roots, so add the nutrient solution little by little afterwards so that the small roots on top do not become submerged. They are the ones that capture the oxygen in the air!
Harvest your salad
After 5 weeks, the salad has drunk about 85-90% of the nutrient solution. It’s time to harvest and then enjoy. To harvest, use a pair of scissors or a knife and cut at the base of the plant. Then clean the system and start again ad infinitum.
We can observe that lettuce grown in Kratky (95.2 g) is heavier than lettuce outdoors (62.5 g). Taste level, they were relatively equivalent. No notable differences.