According to Professor Kratky (link):
Leafy and semi-head lettuce and other short-term crops can be grown with a simple, inexpensive hydroponic kit that does not require electricity or a pump. Once the materials are on hand, the kit takes only about 10 minutes to prepare, and then it requires little attention for the next 5–6 weeks, at which time the lettuce (or other crop) is harvested. There is no need to add additional fertilizer or water—the 1-gallon hydroponic system contains enough plant nutrients and water to grow a short-term crop to maturity. The method is not suitable for long-term crops such as cucumbers and tomatoes, which require large amounts of water.
A Simple Hydroponic Growing Kit for Short-Term Vegetables
by B.A. Kratky, Department of Tropical Plant and Soil Sciences.
What I Learned- Outdoor Kratky Hydroponics – 2014
In this video, Bobby (mhpgardener), recommends this hydroponic nutrient.
