Runoff Numbers - High PPMs and Two Questions

White Widow auto. End of 11 weeks from seed in ground. Soil FFHF + FFOF + Pearlite. Indoor grow. Temps 80 degrees, 45% RH. Light 800 - 1000 PAR. All in flower, several already flushed for harvest over the next week or two. Others may take three weeks or so. All plants look healthy and happy.

Two questions:

  1. Do I need to flush out the non-flushed plants because ppm is so high? They are about three weeks (or more) from harvest.
  2. What should I learn from this data?

Non flushed plants got:
Flowertime Nutes and CalMag at 6.2 pH going in and 30 ppms.

The numbers:

Not yet flushed plants – some really high ppm #s. Water out/ppms out
#7 6.1/3800 ppm
#8 6.2/2800
#4 6.4/2300
#2 Zebra 6.2/2845
#5 6.3/3200

Flushed plants – all under 2000 ppms. Water out/ppms out
#10 6.2/1300
#6 6.3/1976
#9 6.2/1850


These are the plants with the high ppms.

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Hi @GrnyGrows . I had to flush my ww last week. She was up in 3000. flushed til a lot …finally the next reading 2100 ish so…now i wait

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If you choose to flush the plants with the high PPM numbers , I would Follow up with some Bloom nutes. Maybe 1000 PPM Do you normally water or feed to about 20% run off Good luck

Yep I water/feed to run off every time. I’ve been told by a guy who I trust implicitly, that trying to react to ppms in soil is about impossible because we just don’t know if the tds readings are impacted by the dirt in the runoff.

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So, you think I should flush all of them (5) and then next watering start with bloom nutes again?

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I always water to run off I don’t see my numbers climb but I also keep watch on my PH. But if you choose to flush follow up with feeding they will need that to get to the finish line.

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Increasing runoff PPM means the plants are taking in less than you are giving them. This also coincides with the decreasing pH. Nutrients / salts are building up in the rootzone. For me, over 3000 PPM was usually not an issue. I paid more attention to the pH side.
If you are that close to harvest, I am thinking back off on the feed ppm - maybe 50%, and use a higher pH like 6.8 - 7.0. Also have more runoff than normal.
Hopefully this will wash out some of the excess while providing a higher pH late in flower.

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I watch my pH like a hawk and I’m happy with that part of the equation. So, I’ll have to decide what to do.

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Do I need or want a higher runoff ph than 6.2 ish?

Water to run off couple times in a row with ph water 6.5 See if your PPM number comes down.

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Regarding pH & ppm
when I transplant into final containers I get a good amount of runoff. I use it and the next couple as a baseline to gauge where the numbers go later on. My pH rule of thumb was if it changes more than .5 I take corrective actions. I start with mini flushes like I described above (basically overwater to create more runoff)… If the numbers do not change enough, I will flush.
These are pH charts.

If following Kootmed 6.2 is slightly out of range on the low side.

According to growweedeasy it is in range but still on the low side.

I would try to raise it a bit like @kellydans and I described. Feed with a higher pH than you have been using and produce more runoff then normal. Basically trying to raise pH and lower ppm using a light hand rather than flooding it this far along.

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What’s wrong with my pH runoff at 6.1 - 6.2? It’s the ppms that freak me out.

Ah so pH will lower ppms? What? I’m working so hard to learn all of this.

Correct PH will promote uptake for all the nutrients plant needs. PPM should come down with a couple waterings to run off with ph at 6.5

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Oh baby, I’m all over this. We grow, we learn, we laugh at what we don’t know.

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Oh yeah grow grow grow Very enjoyable hobby with a few challenges. We’re all learning and sharing together. Happy growing ! :v:

If pH is too far out of range it can cause nutrient lockout. This basically means now matter how much you feed it it is able to take it in. And thus, it compounds a small issue.

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I understand. I thought runoff of 6.1 or 6.2 was good?

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Overall I think your plant’s look good . I have finished plants In that ph range Without issues, tag back in after a couple waterings on PPM #
Keep up the good work @GrnyGrows

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Thanks a million. I appreciate your knowledge and help.

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