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Never flush a sick plant. Fix the problem or deficiency first. Flushing only compounds problems.
Odds are that your plant diet isn't supplying sufficient immobile nutes and chelated minerals which will cause lock out. You need to get some food back to those plants, but you need to get a balanced dose to em so they will uptake properly.
I water when the pots are dry, and I soak the soil and over watering is never a problem.
I'd mix up a batch of this recipe and feed em all at least twice with it, 3 times wouldn't hurt either.
16 crushed Aspirin,
3/8 cup Brer Rabbit Molasses,
8 tsp Jack's Classic All Purpose (20-20-20),
3 Tbls Epsom Salt,
8 Tbls Lilly Miller Vitamin B1 Plant Starter.
Mixed in 3 cups hot water (boiling hot) to dissolve solids.
Makes 1 quart concentrate. Stored in Refer.
Mixes 16 Gal. @ 1/4 cup per gallon.
Ph 6.5 - 7.
Deficiencies are almost always caused when 1 or more nutrients are not being supplied in sufficient quantities to allow the plants roots to uptake properly.
If all crucial nutrients are being provided in sufficient amounts, salts don't build up and lock out won't happen.
Okay pardner...
You can substitute the Jack's Classic with your own nutes.
The Molasses, epsom salts, and Vit B1 are the keys to this recipe really. The molasses is loaded with vital micro nutes and minerals that help the plant uptake mobile nutes.
Epsom salts keeps your cal/mag in check and the B1 cleans the roots and encourages new growth as well as containing additional chelated minerals to carry other nutes into the plant.
I use Jack's Classic 20-20-20, which recommends a mixture of 1/2 tsp per gallon. My recipe adds 4 gallons extra water and sufficient micro nutes and chelated minerals to prevent uptake problems.
I also NEVER have to flush my plants. Flushing should be reserved for overdoses, and never when plants show deficiencies as flushing them will only compound any deficiencies because it washes any remaining nutrients out of the soil.
So a plant that starts with a minor Iron or Zinc deficiency that's easily fixed with Molasses, can quickly become a major overall deficiency after flushing.