Grow update February 2015

If you follow my posts on Google+, you'll probably know I'm currently running an experiment with growing vegetables hydroponically, in my apartment. I thought I'd share a slightly longer status update here for posterity.

The system I'm using, is the simplest and cheapest I could found, the Kratky method. It is basically a non-translucent container filled with a nutrient solution dissolved in water. The plants are in net-pots hanging in holes in the top of the container.

Initially the net-pots are half-submerged in the solution, giving the young plants loads of water and nutrients. As the water level drops, the plants will chase the water with their roots, while the air-gap causes the plants to grow oxygen-roots. Because of this, it is not necessary to aerate the water, or use some kind of ebb-flow system.

In principle, once the plants are in container, you don't need to do anything else until you harvest them. This method is supposed to work exceptionally well for leafy-greens.


Seeds germinating

For this experiment, I am using three kinds of plants: Lettuce, Amaranth and Basil. To get a sense of how well the seeds I bought germinate, I put some wet paper towel in a box, dropped some seeds on it, and left it a few days in a dark place.

The lettuce did exceptionally well, all the seeds sprouted, the amaranth sprouted a little more than half of the seeds, and only one of the basil seeds sprouted within a week.

Growing the seeds

Coconut fiber pellets

I then put the lettuce seeds, some more amaranth seeds and a whole lot more basil seeds in coconut pellets. I have since found a supplier for rockwool cubes, but at the time it was the best I could found.

Basically, they're coin-sized compressed pellets of coconut shell fiber. Add water, and they expand upwards about 10x, with a hole in the middle. Put your seeds in and add some half-strength nutrient solution to the bottom of the tray. The pellets will wick up the water and stay moist, ideal for sprouting plants.

Nutrient solution


For this first experiment, I'm using a ready-made nutrient mixture (the paper bag at the top of the picture), which contains the correct amount of N-P-K, magnesium, calcium and micro-nutrients. In addition, I also bought a bag of magnesium-sulphate and calcium-nitrate from the same supplier as a starter kit for future projects (the stuff costs almost nothing)

The ready-made mix consists of three separate components. You disolve each of them in a litre of water. To use them, you add each component to the water in the container, in a 1:100 ratio. Very convenient!


Grow container

I'm using two 25L totes as the containers to grow the plants in. I drilled 8 holes in the top with a holesaw and added a water level indicator to the side, with two L pieces and a length of clear tubing.

The water should be enough to support the plants until harvest, but with the very dry climate here in Beijing, I thought it better to keep an eye on it anyway. Once the plants are bigger, it'll be harder to lift the top.

The picture was taking just after I'd transplanted the young plants from the coconut pellets to the grow box. As you can see, I put them in net pots filled with ceramic balls for stability. Once the roots start growing, they'll grow through the net pot into the water.


This time, I built and planted two containers. Unfortunately, only one of the basil plants made it, but both the lettuce and amaranth did very well. I've planted box A with the basil, three amaranth and four lettuce. Box B with amaranth and lettuce half-and-half.

The tap water here in Beijing is heavily chlorinated and has a pH of almost 8. Far to high for the plants I'm growing.

De-chlorinating is easy, since chlorine is a gas, it'll evaporate by itself when you leave the water standing long enough. If needed, you can speed this process up by aerating/circulating the water.

To lower the pH, you basically need to add some kind of acid. This time I used distilled white vinegar, though when I was reading up on it just now, it may not have been the best of ideas. Apparently it's not very stable and can cause slimy roots due to certain enzymes.

I read that car battery acid is a good and cheap way to go. It's 100% pure sulphuric acid, so you need just a few drops to take the pH down, and much more stable.

As an experiment, I'm currently running one container on pH 5.5 and the other on pH 6.0, to see what works better.