Issues that have conflicting solutions

I am typically an outdoor grower, currently in the middle of my trial indoor run. I’ve only one plant, which has been a bit of a change considering I formerly had 28. It is in a closet about 3’x4’, it has a fan on it, some vinegar and baking soda IV drips, and four cfl lights at a 60 watt equivalence and 800 lumens a piece all at 6500 K; with the expectation of adding two 100 watt equivalent bulbs in a week. Anyway, my issues are as follows. My soil is average at best, water retention being it’s main problem. Again, it’s a trial run and I didn’t want to put too much effort and hope in before it was a sincere operation. My plant is mainly healthy and has been for it’s entire growth, (currently around week 6-7 of vegetative.) However, around week 3-4 I noticed a decent amount of leaf stems had become purple. My thought was that there had been no undue stress and it was most likely a magnesium deficiency, so I added some nutrients. Roughly 4-5 days later I noticed some nutrient burn, or so I thought. It made sense to me since I added extra nutrients and wasn’t too concerned since I didn’t add much and after a week it was only on 4-6 leaves in minor amounts. My solution was to give it an extra flushing and maintain watering as normal other than that. More recently I have been noticing fungus gnats, which can cause symptoms similar to that of the nutrient burn. Now I am curious if I misdiagnosed initially or if I have been experiencing both issues. If it is both, how could I solve this? I’d like to keep flushing when I water and keeping the schedule so I can flush out extra nutrients and avoid additional burn, getting tastier smoke as well. I do however use tap water that has low amounts of nutrients in it and if I continue to water normally the soil may not dry enough to help rid of the gnat larvae. I’m considering layering the top with sand to take care of the pests and to continue watering as normal to help with the nutrient burn. Any advice is greatly appreciated.

Yes, purple stems can be a symptom of a magnesium deficiency.

However, all your symptoms together sound like over watering.

Purple stems is often a symptom of over watering. Fungus gnats is also a symptom of over-watering. Over-watering in and of itself can also eventually lead to dying leaf edges, that can look a little like nute burn, as well as damage from the fungus gnats but I think the nute burn might have been from too much epsom salts or other magnesium nutrient supplement.

Don’t worry if the top of the soil feels dry. Judge by the feel of the weight of the container, soil saturated with water as compared to almost totally dry. Use the indoor water method of flooding to saturation once, then letting it nearly dry completely before re-watering or feeding. Monitor the excess run off during watering for pH and nutrient concentrations, i.e. EC/PPM, this will help confirm the reason for nutrient toxicities or deficiencies caused by a pH or you can correct before any problems occur, as well as preventing nute burn by noticing your EC/PPM is getting way too high.

When looking at CFL lights, pretty much ignore the “equivalent” watts, you want to know the real watts it uses, and you will want about 40+ watt per square foot of canopy during flower.

Hope this helps and happy growing,


Thank-you, very helpful. I’m surprised that I’m over watering as the plant is approximately 9 inches tall and VERY bushy, it’s in a 5 gallon pot, and it gets water twice a week at most, as of now. I water until about 20-30% drains out; slightly more alkaline than what’s preferred, which would add to the case that it’s not too much nute burn since it may have minor nutrient lock out, and it is more so the excess water. Which of course I realized when I first saw the gnats. I believe the soil just holds too much. Should I extend my watering schedule from every 3-4 days to every 5-6? In the first 3-4 days after watering, a minimum of three inches top soil is completely dry. I always wait until I have at least three dry inches but usually closer to four. I don’t think I could measure the pots weight since I don’t have a scale it would fit on, don’t trust myself to “eye-ball it,” and I would imagine the plants growth would contribute to a change in the over all weight.

Also, sand for fungus gnats? About an inch or two on top?

I think using DE(food grade) is the better option.

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But sand as a convenient, can get today, cheap solution will work? I’d hate to order something rather than deal with the problem today.

I’m not sure, honestly. Never tried it. It might make it more difficult for the adults to lay eggs in the soil, won’t likely do much for the larva already there.

The DE will kill larva in the soil when it naturally gets watered in. And it will help prevent the adults from landing to lay eggs when sprinkled on the surface.

Bright yellow sticky pads works best for the adults. You can also find both of these potential remedies at a local hardware or garden supply outlet for not very much money. The regular sticky fly ribbons also work in a pinch.

I believe the effect that the sand has is cutting into the adults as they try to move through it. It creates a barrier that should shred them to death as they try to crawl through it. Thus cutting off the ability to penetrate the soil and lay eggs. This wouldn’t kill the existing larvae, but it would prevent new ones and kill them once they reached maturity and have to leave the soil. I will look around the garden store for something better than sand though. So, should I treat the plant as though it doesn’t have nute burn and just focus on the pests?

Yeah, I’m thinking skip a feeding, and of course, water less frequently.

And your sand idea may very well work, let us know. :wink:

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Groovy. Thanks MacG.

It’s actually easier than you think to judge how much water is still in pot by picking it up,you won’t really need a scale as water weighs about 8 pounds per gallon,I was very worried about my judgment as well when I first started but I actually found it was quite easy to know just by picking the pot up

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Sand will do absolutely nothing to expel or stifle the fungus gnat issue. gnats love sand, and bed in sand.

“DE” is the best way. Asked and answered! :slight_smile:

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Just in the knick of time. Thanks latewood.

It has been a few days since I used some diatomaecous earth and it seems to have worked perfectly. I havent seen any adults since, and the plant’s growth seems to be right on track. It is so different growing indoors with a 5 gal. pot versus outdoors in a 100 gal. smart pot. You were more than helpful. Thanks for the help.