I recently decided to build a couple of outdoor hydroponic tanks in a couple of cement raised beds. The beds are 3' by 3' and 10" deep. I lined them with 4 mill plastic. My solution consisted of 20 20 20 and epson salts. I have a 1.5" styrofoam floating surface with 16 K cups inserted. I took lettuce plants from my regular garden, washed off all dirt and planted them in rock wool and put them in the K cups. It has been several weeks now and the plants are really looking pitiful. The roots have gone from white to a dark color and the water really looks bad. Any suggestions?
Josephine County Oregon
Thank you for your question. A Master Gardener in your county has the following to say about hydroponic gardening: https://extension.oregonstate.edu/news/hydroponics-speed-fresh-vegetables-table-growing-water
The one issue that strikes me is the fertilizer you are using. Plants need micronutrients, and most balanced fertilizers do not have those. Your solution might, but you did not say. Nutrient deficiency can lead to a wide variety of plant problems. You also don't indicate what type of aeration system you have, so anaerobic bacteria may have built up, causing the water problem. Here is a bit more involved information: https://gardeningsolutions.ifas.ufl.edu/plants/edibles/vegetables/hydroponic-vegetable-gardening.html
Hope this is helpful. Good luck!
I built my box exactly as it was told in your second link. It calls out 20 20 20 and epson salts. I used the exact measure they called out. Not sure what the micro nutriens are.
The link you're referring to says "Add water-soluble fertilizer, such as 20-20-20 with micronutrients, at a rate of 2 teaspoons of fertilizer for each gallon of water used in the water garden."
Here is a thorough article about what they are, how to apply them, and in what quantities: http://www.greenhouse.cornell.edu/crops/factsheets/hydroponic-recipes.pdf