CANNABIS CULTURE – Ganja Guru Ed Rosenthal on how to stop mineral deficiencies in your garden.
Question: My plants have been flowering a week. I water with 0ppm reverse osmosis water and hydroponic nutrients at 500ppm on rockwool slabs over a 1-inch coco mat. White, healthy roots are exploding out of it and the slabs.
The problem starts at the lower portion of the plant. The side edges of the leaf turn brown, then the leaf turns yellow and curls up. The symptoms work their way up the plant.
Eventually, only the very tops of the plants have flowers.
Why is this happening? What should I do to get better results?
Hal, Los Angeles
Ed Rosenthal: Your plants are suffering from nitrogen (N) as well as magnesium (Mg) Potassium (K), and calcium (Ca) deficiencies. The leaves turning yellow starting at the bottom of the plant are the result of lack of N. It is low in K so the plants send it to the new growth, causing the lower leaves to die. The Mg deficiency results in green veins in the leaves while the rest of the tissue turns whitish yellow. The lack of Ca causes little dead spots throughout the plant, and the slight necrosis on the leaf edges are caused by a K deficiency.
You have the plants on a starvation diet and you are using “dead” water. It contains absolutely no minerals. There is a good reason to use R/O water in Los Angeles, since the salt content of the tap water is around 450ppm. Before you do anything else, enrich the water with a Ca/Mg formula. Most fertilizers are formulated for average conditions, which have some dissolved Ca and Mg. Another way to achieve this result in L.A. is to use 1 part tap to 3 parts R/O water. This raises the Ca and Mg levels and also stabilizes the water so the pH isn’t as variable.
After adjusting the water with Ca/Mg, add bloom nutrients to raise the level to about 1200-1400ppm. Adjust the pH to about 6.1 and you will be ready to roll in a couple of months.
Send your grow questions to Ed Rosenthal at [email protected].