Stunted growth - a repeating problem I can not solve.

Dear fellow growers,

I need your help to figure out a problem with my plants that has been following me for the last 6 grows. I am running a mid-sized operation and It is a repeating problem that I just can’t seem to understand and resolve.

It all goes normal with the seedlings, they are growing well with a light color of the leaves and no visible problems. However, as I approach week 3 of Veg the leaves start to get a darker shade. I have tried to withhold any feeding and wait for them to get lighter but they never do. They never get light but rather darker and when I eventually feed them only the new growth/ top become a bit lighter. I have tried different feeding approaches(more/less) both with the young plants and also later in veg but the result is always the same - dark droopy leaves, clawing and generally a very stunted growth. I have top dressed with worm castings, made teas with just a temporary effect.

Recently I made an observation that the plants don’t develop a very good root system (yes, I could have checked this earlier) . In early veg roots are white, but not that thick or dense. After repot the new roots also appear white. The pictures show the plants in their week 8 of VEG, that is 4 weeks after repotting and the roots don’t seem to be strong or dense. You can also see that the plants are very small for 8 weeks growing.

Later in bloom the roots get brownish and plants start to get yellow with dying leaver starting from week 4 until the end. Plans don’t handle strong light and don’t drink as much. Harvests are poor and generally low quality.

I have posted pictures of a current batch in VEG and in BLOOM. You can see that the roots of both batches are not right. Is this root rot?
I am beginning to think that the problem is not caused by feeding schedule or environment but rather watering and lack of oxygen. I water every other day and generally have a good observation how much they drink every 48h. However, I might have overwatered on repot and didn’t water them for 5-6 days until they got lite. Could that single overwatering start a root rot? Also, would you suggest to put pot elevators and additional perlite to the light mix?

Any suggestions and comments with regards to prevention and current actions are welcomed. I really need your help as this has been happening the last one year and I am running out of ideas and resources.


Environment: Sealed room, CO2 enriched (more info in the attached table)
Media: Plagron Lightmix (preloaded with mineral nutrients for 1-2 weeks at most)
Media pH: 5.8-6.4 (measured with a BlueLab multimedia probe.)
Nutes: Plagron Alga Grow/Bloom (100% organic, seaweed based) (find attached a veg feeding schedule)
Pots: ½ gallon (2L) for the first 3-4 weeks then repot into 2.5 gallon (10L)
VEG/BLOOM: 8 weeks veg and 9 weeks bloom
Lights room1: Chinese LED bar lights with Samsung LH281H chips (cold, warm and UV)
Lights room2: Quantum boards (fotops 800) with Samsung LM301B and IR 3500/4000K
Light schedule VEG: 18/6
Water source: ph 7-8, 60 ppm, filtered through a chlorine filter
Seeds: Skunk XL from Royal Queen Seeds.

Your plants look fine, if maybe a bit overfed in veg, but not serious. Are you saying they are just taking too long to get to this size? If your DLI and VPD are on point, I'd consider experimenting with a different media/nutrient combo. Put in a couple pots with promix or coco and Jacks 321 or even Maxigro/Bloom just for ease of mixing. I'd also maybe try changing up how you feed/water your current plants. Feed a lower EC and be sure they get a wet/dry cycle, try changing things up for a few of your pots and keep track of what you are trying. Those pots are not very big for an organic grow either, so if you want to stay organic, give bigger pots a try-the bigger root volume makes a huge difference in the size of plant in organics. In coco you will see faster growth in 2-3 gallon pots (fed twice daily during flower). If you don't want to feed that often, try promix instead.

In flower your plants look slightly underfed, which bigger pots would fix. If you want to grow plants in pots this size, soilless media + mineral salts are the way to go.

I think you just need to dial in your grow style a bit to get those plants to take off. They don't look bad now by any means.

I agree with @Rurumo, your plants don't look bad. If your concerned about the "lack" of roots, try adding some Azos & Mykos, or Dynamyco at transplant. I've had very good results getting strong roots when adding during transplant.

Rurumo said:

Your plants look fine, if maybe a bit overfed in veg, but not serious. Are you saying they are just taking too long to get to this size? If your DLI and VPD are on point, I'd consider experimenting with a different media/nutrient combo. Put in a couple pots with promix or coco and Jacks 321 or even Maxigro/Bloom just for ease of mixing. I'd also maybe try changing up how you feed/water your current plants. Feed a lower EC and be sure they get a wet/dry cycle, try changing things up for a few of your pots and keep track of what you are trying. Those pots are not very big for an organic grow either, so if you want to stay organic, give bigger pots a try-the bigger root volume makes a huge difference in the size of plant in organics. In coco you will see faster growth in 2-3 gallon pots (fed twice daily during flower). If you don't want to feed that often, try promix instead.

In flower your plants look slightly underfed, which bigger pots would fix. If you want to grow plants in pots this size, soilless media + mineral salts are the way to go.

I think you just need to dial in your grow style a bit to get those plants to take off. They don't look bad now by any means.

Click to expand...

Thank you for the input, let me bring some more info with regards to your concerns and suggestions.

DLI and VPS should be on point. I run 18h in Veg under 400-500 ppfd LED which by all standards is optimum. VPD was a huge topic of research for me and I have finally set it to 70-80% humidity and 27-29 degrees (80-85f) for VEG (Under led you need higher temps to compensate for lack of IR) There is a lot of controversy around VPD. Some people seem to grow successfully outside VPD practice, but I've decided to follow the tables.

At this point I am reluctant to change media/nutrients as I know people who have success with this combo and it is too risky to make general changes. Experiments take a lot of time too. My best course of action right now is to adjust my current method to satisfactory results.

I'm currently feeding around 500ppm (Feed, Feed, Water), will take your advice and lower to 400ppm, possibly Feed-Water until they recover.

With regards to pots size, I don't tent to grow the plants much bigger and also I think this size has much more potential for root density and quality than what I am currently achieving.

Wet and Dry cycles is possibly the closes to what might be the problem. Currently I water the VEG plants with 0.4L every other day. I am being suggested to water say 0.6L-0.7L every 3 days and give them more time. I've been doing this to avoid overwatering but the effect might be negative because they dry too quickly and the pot does not get evenly moist.

Plants in flower started yellowing aggressively starting week 4, I have removed a lot of yellow leaves. Gave them 3 consecutive feeds of 600-700ppm which did not stop the yellowing and finally reduced the light from around 700ppfd to 500 and the yellowing stopped. I believe that the weak root system just can not keep up with recommended light intensity and basically the damage with them is done in veg.

Kgrim said:

I agree with @Rurumo, your plants don't look bad. If your concerned about the "lack" of roots, try adding some Azos & Mykos, or Dynamyco at transplant. I've had very good results getting strong roots when adding during transplant.

Click to expand...

I am sure those additives are great and I've tried adding Mycorrhiza with no visible results. I use Rhizotonic by Canna, but still think that my issues are more general and not a matter of micro improvements. I'm sure there are people who have better results than me with just the basic nutrients and nothing else.

Your plants are sitting in runoff water.

Ya you want to elevate them

plan500 said:

Dear fellow growers,

I need your help to figure out a problem with my plants that has been following me for the last 6 grows. I am running a mid-sized operation and It is a repeating problem that I just can’t seem to understand and resolve.

It all goes normal with the seedlings, they are growing well with a light color of the leaves and no visible problems. However, as I approach week 3 of Veg the leaves start to get a darker shade. I have tried to withhold any feeding and wait for them to get lighter but they never do. They never get light but rather darker and when I eventually feed them only the new growth/ top become a bit lighter. I have tried different feeding approaches(more/less) both with the young plants and also later in veg but the result is always the same - dark droopy leaves, clawing and generally a very stunted growth. I have top dressed with worm castings, made teas with just a temporary effect.

Recently I made an observation that the plants don’t develop a very good root system (yes, I could have checked this earlier) . In early veg roots are white, but not that thick or dense. After repot the new roots also appear white. The pictures show the plants in their week 8 of VEG, that is 4 weeks after repotting and the roots don’t seem to be strong or dense. You can also see that the plants are very small for 8 weeks growing.

Later in bloom the roots get brownish and plants start to get yellow with dying leaver starting from week 4 until the end. Plans don’t handle strong light and don’t drink as much. Harvests are poor and generally low quality.

I have posted pictures of a current batch in VEG and in BLOOM. You can see that the roots of both batches are not right. Is this root rot?
I am beginning to think that the problem is not caused by feeding schedule or environment but rather watering and lack of oxygen. I water every other day and generally have a good observation how much they drink every 48h. However, I might have overwatered on repot and didn’t water them for 5-6 days until they got light. Could that single overwatering start a root rot? Also, would you suggest to put pot elevators and additional perlite to the light mix?

Any suggestions and comments with regards to prevention and current actions are welcomed. I really need your help as this has been happening the last one year and I am running out of ideas and resources.


Environment: Sealed room, CO2 enriched (more info in the attached table)
Media: Plagron Lightmix (preloaded with mineral nutrients for 1-2 weeks at most)
Media pH: 5.8-6.4 (measured with a BlueLab multimedia probe.)
Nutes: Plagron Alga Grow/Bloom (100% organic, seaweed based) (find attached a veg feeding schedule)
Pots: ½ gallon (2L) for the first 3-4 weeks then repot into 2.5 gallon (10L)
VEG/BLOOM: 8 weeks veg and 9 weeks bloom
Lights room1: Chinese LED bar lights with Samsung LH281H chips (cold, warm and UV)
Lights room2: Quantum boards (fotops 800) with Samsung LM301B 3500/4000K
Light schedule VEG: 18/6
Water source: ph 7-8, 60 ppm, filtered through a chlorine filter
Seeds: Skunk XL from Royal Queen Seeds.

Click to expand...

So if you want to increase drainage, reduce moisture retention, and provide more airflow to the medium, it's pretty straight forward. Perlite can be used ad nauseam. You can drill holes in the sides of your containers as well.
What are your watering habits like throughout the grow? How's your medium on average? Are you adjusting watering before or after the plant wants to drink more/less from stage to stage?

I've had this issue in the past. Can't say with 100% certainty it's overwatering in your case, but I overwatered and that's exactly what happened to me

I don't know what others are going by but those plants don't look fine to me. The leaves should not be dying and yellowing. I don't know why so many seem think that's normal and fine these days. They should not have all those yellow dying leaves at the stage they are in. The root development looks poor as well. It's too late to do much at this point other than just keep feeding them until they're finished.

I'm not a fan of those organic beet vinasse/molasses based nutrients. I know many want to go all organic but you'll likely have better success and healthier plants using a salt based product like MaxiBloom.

Seems like you spent more time studying charts about VPD, ppfd, etc... rather than basic plant nutrition. That Plagron LightMix is basically just peat and perlite with a very minimal amount of some minerals added. 500 ppm seems low for flower growing in that mix.

plan500 said:

Thank you for the input, let me bring some more info with regards to your concerns and suggestions.

DLI and VPS should be on point. I run 18h in Veg under 400-500 ppfd LED which by all standards is optimum. VPD was a huge topic of research for me and I have finally set it to 70-80% humidity and 27-29 degrees (80-85f) for VEG (Under led you need higher temps to compensate for lack of IR) There is a lot of controversy around VPD. Some people seem to grow successfully outside VPD practice, but I've decided to follow the tables.

At this point I am reluctant to change media/nutrients as I know people who have success with this combo and it is too risky to make general changes. Experiments take a lot of time too. My best course of action right now is to adjust my current method to satisfactory results.

I'm currently feeding around 500ppm (Feed, Feed, Water), will take your advice and lower to 400ppm, possibly Feed-Water until they recover.

With regards to pots size, I don't tent to grow the plants much bigger and also I think this size has much more potential for root density and quality than what I am currently achieving.

Wet and Dry cycles is possibly the closes to what might be the problem. Currently I water the VEG plants with 0.4L every other day. I am being suggested to water say 0.6L-0.7L every 3 days and give them more time. I've been doing this to avoid overwatering but the effect might be negative because they dry too quickly and the pot does not get evenly moist.

Plants in flower started yellowing aggressively starting week 4, I have removed a lot of yellow leaves. Gave them 3 consecutive feeds of 600-700ppm which did not stop the yellowing and finally reduced the light from around 700ppfd to 500 and the yellowing stopped. I believe that the weak root system just can not keep up with recommended light intensity and basically the damage with them is done in veg.

Click to expand...

One guy said elevate pots, though I can't see them sat in run off it's possible if the drainage holes in those sorcers are all on the bottom.

Can't hurt either way.

Your temps are what I would run in a non co2 enriched environment.
Personally I'd try raising them a bit.

You said you lowered light intensity and the yellowing reduced, so they aren't getting optimal everything and as a result your plants aren't keeping up with the light your trying g to hit them with. My guess is if you up temps you'll get better growth in veg and happier plants in flower.

Also addi g perlite next round would be worth a shot and if I ever use plastic pots (I do in veg)
I drill holes 2" apart across the whole of the bottom 3rd of the pot. This will cause some root pruning and you'll have a bigger root mass by the time flowering starts

Nutrient water corrodes aluminum btw, and it can leach contaminants. There is a reason they don't use aluminum heat exchangers in reservoirs, etc. I know its just runoff in this case, but it appears the plants are sitting in it as it occurs (how can't they without being elevated?), and even looks like there is standing water in one of the pans in the pics.

If the pots are being watered, and they are sitting on the bottom of the pie pans, even if you emptied it afterwords, or it was only for a few minutes, it didn't really get proper drainage. IMO anyway

xtsho said:

I don't know what others are going by but those plants don't look fine to me. The leaves should not be dying and yellowing. I don't know why so many seem think that's normal and fine these days. They should not have all those yellow dying leaves at the stage they are in. The root development looks poor as well. It's too late to do much at this point other than just keep feeding them until they're finished.

I'm not a fan of those organic beet vinasse/molasses based nutrients. I know many want to go all organic but you'll likely have better success and healthier plants using a salt based product like MaxiBloom.

Seems like you spent more time studying charts about VPD, ppfd, etc... rather than basic plant nutrition. That Plagron LightMix is basically just peat and perlite with a very minimal amount of some minerals added. 500 ppm seems low for flower growing in that mix.

Click to expand...

Agree that 500 is way low for larger flowering plants. Also agree they’re not looking good. Also wondering about light intensity and PAR.

Drop That Sound said:

Your plants are sitting in runoff water.

Click to expand...

Not really as I never have runoff, except when the soil is very dry and some water drains through the cracks in the tray. Part of the problem is that I can not afford to have runoff as there are too many plants to empty each tray.

Drop That Sound said:

Ya you want to elevate them

Click to expand...

I will do that in the following days. If not for the run off so much at least to get some air to the bottom holes.

Killaki said:

So if you want to increase drainage, reduce moisture retention, and provide more airflow to the medium, it's pretty straight forward. Perlite can be used ad nauseam. You can drill holes in the sides of your containers as well.
What are your watering habits like throughout the grow? How's your medium on average? Are you adjusting watering before or after the plant wants to drink more/less from stage to stage?

Click to expand...

Adding additional 10% perlite to the mix in in my list for the next batch. Drilling hole and placing wooden pot elevators too. In terms of watering so far I've been trying to predict how much they drink and water every 48h. Top watering starting 100ml , around 0.5L in mid Veg week 4 and by the end veg week 8 I can get up to 1L every 48h. The main problem I see now and hear from people is that I should aim for watering more and less often, so that the pot gets wet evenly and dries out slower. I'm already testing this as of today. Instead of watering 0.4L I did 0.7L and will wait until they are dry before I repeat.

Gotcha. Wood and water might cause problems. I would probably use cheaper corrugated PVC or galvanized roof panels, and make large slightly sloped drain tables that runoff into a gutter, just like the roof on most houses, for super cheap. Not up high, but low to the ground. Use free pallets as the framing, etc. Never deal with saucers again...

xtsho said:

I don't know what others are going by but those plants don't look fine to me. The leaves should not be dying and yellowing. I don't know why so many seem think that's normal and fine these days. They should not have all those yellow dying leaves at the stage they are in. The root development looks poor as well. It's too late to do much at this point other than just keep feeding them until they're finished.

I'm not a fan of those organic beet vinasse/molasses based nutrients. I know many want to go all organic but you'll likely have better success and healthier plants using a salt based product like MaxiBloom.

Seems like you spent more time studying charts about VPD, ppfd, etc... rather than basic plant nutrition. That Plagron LightMix is basically just peat and perlite with a very minimal amount of some minerals added. 500 ppm seems low for flower growing in that mix.

Click to expand...

If you refer to the plants in flowering, then I agree and the damage there is done. Right now I am more focused to understand the cause and do adjustments to the next batch or the one after. The sooner I figure this out the less pain

Regarding the nutes, they are recommended by many people including my friends and I now that good results can come from that specific brand/type. Also I chose organic because I dont have to deal with ph and also they say it is hard to overfeed when all other factors are right.

It's true I've gone deep into details and miss the important foundation. I used to grow in coco with automatic irrigation and soil is relatively new for me. I am aware that the lightmix is almost like hydroponics medium but 500ppm food is my target in mid-to-late veg. Consider as well a Feed-Feed-water model. My buddies, who use this nutes never go above 500ppm and rarely give 3 consecutive feeds.

plan500 said:

Adding additional 10% perlite to the mix in in my list for the next batch. Drilling hole and placing wooden pot elevators too. In terms of watering so far I've been trying to predict how much they drink and water every 48h. Top watering starting 100ml , around 0.5L in mid Veg week 4 and by the end veg week 8 I can get up to 1L every 48h. The main problem I see now and hear from people is that I should aim for watering more and less often, so that the pot gets wet evenly and dries out slower. I'm already testing this as of today. Instead of watering 0.4L I did 0.7L and will wait until they are dry before I repeat.

Click to expand...

Water by weight. Not by “it’s dry to my second knuckle”. Not by a schedule. After transplant pick it up before watering it in. Then use the proper volume to water it in. Pick it up. A 5 gallon container should easily absorb 1 gallon without any problem. That’s 1 gallon minimum first time and should be close to that volume without excessive runoff every time.

coreywebster said:

One guy said elevate pots, though I can't see them sat in run off it's possible if the drainage holes in those sorcers are all on the bottom.

Can't hurt either way.

Your temps are what I would run in a non co2 enriched environment.
Personally I'd try raising them a bit.

You said you lowered light intensity and the yellowing reduced, so they aren't getting optimal everything and as a result your plants aren't keeping up with the light your trying g to hit them with. My guess is if you up temps you'll get better growth in veg and happier plants in flower.

Also addi g perlite next round would be worth a shot and if I ever use plastic pots (I do in veg)
I drill holes 2" apart across the whole of the bottom 3rd of the pot. This will cause some root pruning and you'll have a bigger root mass by the time flowering starts

Click to expand...

I will elevate them, won't hurt.
I agree about the temps, I was aiming at 29 degrees in veg and around 30 in flower, but then with all issues and unhealthy plants I've reduced it a but although I run C02 in flower at around 1200ppm. Perlite and more holes are already in my list.