Seedling devope black spots and die in rockwool

michael_j_wApril 22, 2009

Hello All,

I am becoming very frustrated because every seedling i germinate dies. I am using Grodan Delta mini-blocks (1.5x1.5x1.5). I soak the blocks in 5.5 ph adjusted distilled water with 5ml/gal of Age Old Organics Grow fertilizer. The seeds (lettuce, basil, chives, oragano, sage, and tyme) germinate and sprout in 3-5 days. The seedling leaves open and the plants either stall here or some get their first true leaves and stall. After a week or so past the point of stalling the stems and leaves develope black spots which spread and the plants die in 1-3 weeks. I have been watering a little bit with the same solution i soaked the cubes in, but there is no standing water in the flat. I have tried keeping the dome on, partially on, and without a dome, it doesn't seem to matter. The guy who runs the local hydro shop said they just needed more nutrients, so i put a few of the most healthy plants in a "daisy cloner" style aeroponics bucket. They got black spots on the stems (right where they emerge from the cubes) two days later. I think the rockwool is smothering the roots, but as i am a neophite my opinion isn't really based on any experience. My only reason for thinking this that of the few plants which have shown any roots from the bottom of the cubes, all have gone from white to brown to black as the plant gets more spots and then dies.

These plants will be put into net pots and hung in a 4x4 vinyl fence post nft system if can get enough roots to grow.

Any help would be appriciated.


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Hi michael,
Consider the rockwool may be retaining fertilizer & you are getting a build up in the substrate.
It is then a toxicity, rather than symptoms of nutrient deficiency. Your seedlings become vulnerable to this external ion concentration actually pulling out from the plant tissue.
The black spots are indications of necrosis, but not from lack of nutrient supply - more from overkill.

    Bookmark   April 23, 2009 at 5:53PM
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