Want a convenient source of tasty, fresh and healthy salad greens? Using a variation of the methods described by B.A. Kratky in 2009, it is possible to grow a continuous supply of lettuce (and other leafy veggies) in your home year round. This method has a low startup cost and is easy to follow with little time, space or experience required.
While this system is not limited to lettuce, it is most successful with leafy, green vegetables. As such, lettuce provides many benefits to the beginner including being easy to grow, requiring relatively low levels of light and having a short growing period from seed to harvest. (6 to 8 weeks max)
In short, the lettuce is "planted" in a soil-less medium suspended in the lid of a small container. The container holds a nutrient solution that provides the building blocks needed for the lettuce to grow. The roots of the lettuce grow down into the nutrient solution and take up the solution at the needed rate. As the water level drops, the roots continue to grow and so are always able to reach the solution. The air space above the water provides the oxygen needed by the plant’s roots for growth. Of course this all depends upon the plant receiving sufficient light (energy) to grow. Since we are growing indoors, artificial lighting will almost certainly be needed.
In contrast to commercial hydroponics systems, the Kratky method does not require expensive, specialized equipment and does not depend on pumps for water circulation and aeration. Lettuce can be grown in recycled bottles or similar containers. Lighting can be provided by an inexpensive shop light or common light fixtures hung close to the plants. While I suggest a couple of items that can be purchased online for the beginner, the system is flexible and you will find that substitutions can be used when you are comfortable with the process and understand the (minimal) needs of the plants.
Starting lettuce seeds is very easy. Using a small cup and some tap water, submerge a few seeds overnight. Decide how many plants you want in a batch and soak a seed or two more in case some of your seeds fail to germinate. In less than 24 hours you should be able to see roots beginning to emerge from the seeds. Using method, I have nearly 100% success rates of germination.
When you see the root emerging, you have confirmed that the seed is viable and ready to be "planted". The rockwool cubes that I use have wells formed into the top into which you will place the viable seeds. Simply soak the cubes with plain water and place one seed into each cube. Place the cubes in a shallow container with a small amount of water in the bottom to keep the cubes moist. Cover the container with a clear lid or plastic wrap and place in a window or under a light until the leaves of the seedlings begin to emerge.
Once two to four leaves have emerged from the cubes, you are ready to place the plants in their final growing containers. First, place a net cup into a hole cut into the lid of your container. Place this in your container and note how far down into the container the cup reaches. Fill the container with nutrient solution mixed using the manufacturer's instructions. I tend to lean toward weaker nutrients because over fertilization can easily "burn" the tips of lettuce leaves.
Now you can place the lid (and net cup) back on your container. Put the rockwool cube into the net cup and double check that the bottom of the cube reaches the solution. As the roots of the lettuce plant grow down out of the cube, they will begin to pull up solution to the growing plant. As the level of the solution goes down, the roots will continue to grow down as well.
Place the new plant in a south facing window or under a strong artificial light source. As a point of reference, I have had good growing success for lettuce using one 26 watt compact fluorescent bulb for every two lettuce plants. I keep the lights about 4 to 6 inches above the tops of the plants to make sure they get plenty of light but this is not so close that the heat from the bulbs damages the plants.
From this point, the plant pretty much takes care of it self. There should be no need to refill the grow solution and being indoors, there is little problem with pests or infections. I use a timer on my lights and give them 16 hours a day of light and 8 dark hours of "rest".
IMPORTANT: Never completely re-fill the container with solution while a plant is growing there. This is the KEY to the Kratky method. Some of the roots reach down to pull up water, while others will pull in air from the space above the solution. If you refill the container once there are roots growing out of the rockwool cube, you run the risk of drowning those roots. If you feel the need to add solution, I would limit yourself to filling up to a level no more than one third of the capacity of the container. Indoors, at the point that you run out of solution, the lettuce is likely reaching the end of its harvestable life.
I personally use the "Cut and Come Again" method. My strategy is to start a new batch of lettuce at the beginning of each month. As the older plants approach the end of their productive lives, the youngest plants are probably ready to start being harvested from or will be shortly. At any given time, I have three generations of plants growing: Two generations that I am harvesting from and one that is in the early growth period and being left alone. At the beginning of each month, I send what is left of the oldest plants to the compost bin and use the containers to start a new batch. What had been the youngest batch is probably ready to start being harvested from or will be shortly.
All content © 2015 by Chris Dahl