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.
Kratky Lettuce

What I Learned- Outdoor Kratky Hydroponics – 2014







In this video, Bobby (mhpgardener), recommends this hydroponic nutrient.