To Flush or not to flush (soil grow)

So I keep reading on multiple forums that FF sledgehammer can straight up ruin a grow.

I see multiple ways people are doing the FF flush. Some claim success, some claim total ruin.

From reading the instructions, you add 2tsp to a gallon of water and that’s it. Done.

Do you have to actually “flush” or rinse out the Sledgehammer out of the soil?

Can any remaining sledgehammer leech all your nutrients?

I’m tempted to just use PH’d water to flush

I invite input from all soil growers. Do you flush at transition? What if your plants are showing no signs of abundance or deficiency?

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I flush if problems warrant it. It could be an excess, but what I usually run into is problems keeping pH in range later in the grow after salts have had a chance to accumulate. I do use Sledgehammer and it has worked fine for me. I have 10-gal pots and I usually run through 3 gallons of Sledgehammer mix and then follow it up with 6 - 8 gals of straight up distilled to wash out the sledgehammer and salts.

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Those having issues after flushes likely aren’t adding the feed back in after the flush or not flushing out the sledgehammer. With sledgehammer, I pour it in the soil and let it sit for about an hour then rinse the sledgehammer out with 5 gallons or so. Then the last gallon that goes in is my nutrient solution.


How many times during a grow do you flush? Is it scheduled or do you just wait for the runoff PH to be low ? And how low is too low for Runoff?

If using fox farms nutes, every 4 weeks. But only in flower as I don’t typically add nutes during veg

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Most flushes will occur during flowering when you want your pH to be on the higher end of the range to help P and K uptake. I target 6.5 - 6.6.

I never flush unless there is a reason to, but FF recommends 3 flushes for a whole grow. The schedule is on their feed chart. I don’t know what the other nute makers recommend.


How do you get the runoff to match what goes in? I’m having a problem with that.

I just used Sledgehammer on three plants just before putting them into flower. Three different strains. Two of the three did fine, one of the three had crinkled leaves. I reread the instructions on the bottle, I did it right. Reread the instructions on the feeding schedule, and there at the top, it says Sledgehammer should be combined with a nutrient. With soil, it’s supposed to be combined with Boomerang. With hydroponics, it’s supposed to be combined with Big Bloom. Who knew? Maybe that’s all it will take to eliminate the problems people are having with it. It will be awhile before I get to try again.

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I flushed with ffsh. Then just gave water. One plant did t care, three just stopped growing so I’m not doing that again unless I see a problem

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I just flushed. I used 3 gallons of FFSH and then 12 gallons of 7.4ph water. 6 gallon plastic pot. I brought my runoff PH to 6.1 from 5.6

After a long debate I decided to only Sledgehammer flush one of my two photo plants.

We’ll see how it goes.

@NeoGroR I’m considering flushing with sledgehammer, and would like to know how your experience went. I’m Having pH issues with ffof, already supplementing with cal/mag to try and address issue, but need to raise pH. Already implemented dolomite lime.

It worked great. I flushed one gallon mixed with sledgehammer and then waited 15 minutes and flushed with a ton of water. It was probably 8-9 gallons maybe more. I have 6 gallon plastic pots.

My pH was still a little low, but I guess that’s normal. I top dressed with some Lime and I’ve been good since.

It’s a lengthy process. Allocate some time. @Keetz

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Really dumb question as I’m still having some problems with pH. Are you doing the lime dressing before watering or after? I’ve been doing it before, and only managed to get my pH up to about 6.11 - don’t want to keep adding and watering it it is supposed to go on after watering and allowed to deep down…

Nervous about the flush, but one of my girls looks terrible after 3 weeks of my treating for cal/mag def and low pH. FFOF…

6.11 is good. You’re good

@NeoGroR thanks- the flush seems to have done a lot of good as well, read this post a few times prior to flushing. Just gotta maintain now! Got my 2nd lady up to 6.23! Long journey from 5.47…

Good luck!

I only got mine up to 5.7 on one of my plants. I was told somewhere that the decomposition of some of the organic material in the pot will cause some acidity. So I rolled with it and didn’t focus too hard in my F’d up pH levels.

It worked out. I have a great harvest drying in a closet now. Huge buds.

My next go around i mixed in some dolomite lime to the soil. We’ll see how they do. They’re about to be flipped to flower


Damn, Hoping mine turn out that nice looking! Think I’m just gonna keep going with the dolomite lime dressing then water with each watering. The lady I flushed with info on this post is looking so much better! So, thanks @NeoGroR and @CMichGrower and everyone else!!!

From the day of the flush to today -


I recently had an outdoor plant in 10 gal fabric pots, FFOF soil, present a major pH problem, checking runoff showed 4.9

I used 2 gallons of sledgehammer mix then flushed the plant, letting the hose run on it slowly for a few hours and was able to bring it to 6.2ish…followed up with a nutrient rich watering the next morning and the girl couldn’t be happier