Dirtbag
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I give plain water for the last 7-10 days. So does every grower I know, and that's personally dozens of growers in my neighborhood. I have had pot that burns black ash and goes out a lot, mostly from Hydro grows that haven't flushed properly, but I've also had promix grown pot that is harsh and burns black too. Maybe from over feeding, not sure.
But my reasoning for plain water the last week or so is simple; promix has a cation exchange capacity. It's not inert and holds on to nutrients to a degree, which it can release to the plants if needed. It's why I can get away with multiple water only feedings mid cycle before seeing deficiencies. By giving just water at the end the plants can use up what little they need from the stored cation bank, or from the leaves. Essentially they just dont need a lot of input the last week or two.. maybe a little potassium sulphate, but that's it.
Now I'll freely admit I have no science to back this up, just anecdotal evidence.
Hydro and coco are a different story. You should feed those what they need to within days of the chop. But any media with a CEC should have plenty of stored nutrients to make the last week or two without feeding added nutes.
But my reasoning for plain water the last week or so is simple; promix has a cation exchange capacity. It's not inert and holds on to nutrients to a degree, which it can release to the plants if needed. It's why I can get away with multiple water only feedings mid cycle before seeing deficiencies. By giving just water at the end the plants can use up what little they need from the stored cation bank, or from the leaves. Essentially they just dont need a lot of input the last week or two.. maybe a little potassium sulphate, but that's it.
Now I'll freely admit I have no science to back this up, just anecdotal evidence.
Hydro and coco are a different story. You should feed those what they need to within days of the chop. But any media with a CEC should have plenty of stored nutrients to make the last week or two without feeding added nutes.