Can't keep seedlings alive

As the title says, my seedlings just keep dying and I can't figure it out.

I've grown in soil years ago and had no problem growing until harvest, but now I'm trying my hand at an indoor DWC grow and just can't keep the seedlings alive.

In an earlier thread I posted about yellowing veins in my seedlings and @OldMedUser clued me in that I overfed them big time. Unfortunately, even after swapping the res with pure PH'ed water those seedlings remained growth stunted so I eventually tossed them.


So I started a new batch with a much lower feed than the GH recommendation:

Week 1:
Distilled water and about 2mg / Gal of CalMag.
PH measured around 6.0 using a digital reader, and verified with a chemical PH kit.
EC/TDS measured around 200 ppm.
Light height was about 20'' and at 25% power. Measured about 7000 Lux using an app (can't afford a fancy PAR meter).

The seedlings were stretching (see photo) so I bumped the light power up to 50%.

Week 2:
Around 1mg/Gal each of the GH Flora series.
EC measured 290ppm.
PH was around 5.9.

I'm in week 3 now and the plants look pretty fucked:




Could they be light-stressed now? The far right and near right plants are showing burned edges.

The left center plant is showing yellowing veins, and far left plant is wilting.

One interesting detail: I have other plants (tomato, cilantro, basil, sage, rosemary) in the same grow tent, none of which have burnt edges like this.

If it is indeed light stress / LED burn, can they recover from this or should I start a new batch?

Thanks for any advice!

If anything it looks like they aren't getting enough light or did they grow stretched up like that before putting them in the tub?

You shouldn't be covering up the net pots like that. Just add more balls to block any light or you risk stem rot from all the moisture trapped around the base. I'd boost your calmag to 4ml/gal at nute change but you shouldn't have to change nutes for a while now.

You'll learn a lot more keeping these girls going rather than starting from scratch again where you will likely end up with the same results.

You should never switch from running nutes to just water as that can really fug up and even kill your plants. When the nutes were too high it's best to just remove some of the nutes and replace with RO or distilled water to reduce the ppm. Or rinse out and replace with a lower level nute mix. might want to lower the pH to around 5.6 and see if that helps. Mine would always rise to about 6.3 every 3 days when I did my top-ups so I'd knock it down to around 5.3 with a few drops of conc. sulphuric acid and it would go back up like clockwork which is actually good for the plants. Then I got AN pH Perfect nutes and retired my pH pen. Just top-up with RO water and check ppm which would drop so I'd add small amounts of nutes in the same ratio to bring it back up to target.

Thanks for swooping in to help again @OldMedUser!

They were stretching from the very beginning - I put them in the tub immediately when they showed cotyledon leaves because I was worried they would experience transplant shock if I moved them at a more mature stage. Once I noticed them stretching I bumped up the light intensity to 50%, but after seeing the burnt tips I dropped it to 30% and changed the period from 18/6 to 16/8, thinking they were burning.

With the last batch I gradually diluted the res initially, but they continued to burn up at the edges so I moved a few plants into kratky pots (in my case just clean soda cans) with pure water to act as controls for the next attempt. Those controls remained growth stunted for weeks so I ditched them :/

After posting this thread earlier I got so frustrated I swapped out the res and even swapped the container with a spare. I've tried varying so many factors and end up with the same burned tips, I figured maybe the container itself had something toxic in it.

Should I try increasing the intensity of the light or maybe lower the height from 20'' to 16'' or so?

EDIT: good point about covering the base with beads instead of foil, I'll fix that tomorrow.

gwarf said:

As the title says, my seedlings just keep dying and I can't figure it out.

I've grown in soil years ago and had no problem growing until harvest, but now I'm trying my hand at an indoor DWC grow and just can't keep the seedlings alive.

In an earlier thread I posted about yellowing veins in my seedlings and @OldMedUser clued me in that I overfed them big time. Unfortunately, even after swapping the res with pure PH'ed water those seedlings remained growth stunted so I eventually tossed them.


So I started a new batch with a much lower feed than the GH recommendation:

Week 1:
Distilled water and about 2mg / Gal of CalMag.
PH measured around 6.0 using a digital reader, and verified with a chemical PH kit.
EC/TDS measured around 200 ppm.
Light height was about 20'' and at 25% power. Measured about 7000 Lux using an app (can't afford a fancy PAR meter).

The seedlings were stretching (see photo) so I bumped the light power up to 50%.

Week 2:
Around 1mg/Gal each of the GH Flora series.
EC measured 290ppm.
PH was around 5.9.

I'm in week 3 now and the plants look pretty fucked:


View attachment 5158296

Could they be light-stressed now? The far right and near right plants are showing burned edges.

The left center plant is showing yellowing veins, and far left plant is wilting.

One interesting detail: I have other plants (tomato, cilantro, basil, sage, rosemary) in the same grow tent, none of which have burnt edges like this.

If it is indeed light stress / LED burn, can they recover from this or should I start a new batch?

Thanks for any advice!

Click to expand...

If you start with really good soil, like Ocean Forest, you don’t need to apply nutes. The soil should hold it until they get bigger and stronger. Be careful not to overwater, too. They look like they are stretching for light. Are your lights too hot to bring them closer?

@MinniePerlite thanks for the tip. This is a DWC grow, so no soil. Just rapid rooters and hydroton in net pots over a 2 gal reservoir.
The light is an LED Viparspectra p1000: https://www.amazon.com/VIPARSPECTRA-Upgraded-Spectrum-Dimmable-Hydroponic/dp/B083JVXHF6

It doesn't *feel* too hot to lower the light, so I'll try that, thanks!

Dosent even look like weed. Um what kind of ph instrument do ypu use to check your ph. All your plants look like they are yellowing indicating some kind of issue taking up nutrients. They should have plenty to eat they need basicly very little at that stage. So we need to know more details. It's def something your doing

@ProPheT 216 lol yeah that one is rosemary.

I use a digital PH meter and verify it with a chemical PH test.
The digital PH meter is this one: https://www.amazon.com/VIVOSUN-Meter-Digital-Tester-Water/dp/B01M5IASHD
And the chemical PH test is the one that comes with the GH PH kit here: https://www.amazon.com/General-Hydroponics-pH-Control-Kit/dp/B000BNKWZY/ref=psdc_3238155011_t1_B07QNCBL7S

I started with distilled water, added 2mg/Gal of CalMag (EDIT: and about 1mg/Gal of each of the GH Flora series) and that dropped the PH to around 6.0 without needing to add PH-down.

I'll try calibrating my PH meter and re-check.

They look alive to me?

You know what, it might be a potassium issue that's hard to identify because they're all so immature. You have distilled water, Cal-Mag, and... peat/coconut coir, right? I have a feeling as though you're missing some minerals.

I recommend taking some traditional (organic) potting soil and mixing it with the coir/peat at a 5:1 ratio (more peat/coir than soil). Instead of using distilled water, try using spring/purified water. The potting soil shouldn't hurt your hydroponics, but it would add some vital minerals and beneficial microorganisms. Seedlings don't need a lot of nitrogen, but they still need minerals to help various cellular functions.

Alternatively, you can try using something like Fox Farm Kangaroots with spring/purified water.

I say it's ph. No reason they should not have enough nutrients. My ph pen probably show a totally different ballpark than yours. Do u have calibration packs or.fluid. see of it reads 4.0 and 7.0 accurate if u do

@calvin.m16 yeah they're alive for now - but they're showing such distress early on that I don't believe they'll survive, especially since I can't pinpoint what causes this.

@King Dude I'm hesitant to use soil in a net pot in DWC, the soil might crumble through into the reservoir. Right now I'm using rapid rooters in hydroton, I've heard others use the same setup so in theory it should work?

@ProPheT 216 I think you're right. I just measured distilled water straight from the bottle and it shows a ph of 6.0, which is wrong. That means I've likely been feeding them with a PH of 7 or above, thinking it was 6. I have the calibration packs for the PH pen and I'm in the process of wiping out containers to do the calibration now, I'll post again with results.

EDIT: Yep after calibrating my PH pen I re-tested the res and it was 7.6. I'll gradually add some ph-down'ed water to the res to bring it back to normal and see if the plants improve. Thanks again to everyone for all the help so far!

gwarf said:

@calvin.m16 yeah they're alive for now - but they're showing such distress early on that I don't believe they'll survive, especially since I can't pinpoint what causes this.

@King Dude I'm hesitant to use soil in a net pot in DWC, the soil might crumble through into the reservoir. Right now I'm using rapid rooters in hydroton, I've heard others use the same setup so in theory it should work?

@ProPheT 216 I think you're right. I just measured distilled water straight from the bottle and it shows a ph of 6.0, which is wrong. That means I've likely been feeding them with a PH of 7 or above, thinking it was 6. I have the calibration packs for the PH pen and I'm in the process of wiping out containers to do the calibration now, I'll post again with results.

Click to expand...

If you have to get a better pen go with this 1. Great value for money

The rapid rooters shouldn't really be soaked like that. (middle right plant) It's the same as over watering a seedling in soil at this point,

Your water level is too high i'm guessing?

The rooter plug should be up high enough, or the nutrient solution level low enough, that it just mists the bottom of the plug\pepples, and starts to dry out enough, but also encourages the tap roots to shoot down in search of water.

You'll have problems if the upper area of the net pots is wet, going up close to the stalks, like Old Med says.

Not sure why you need calmag. Ditch all the additives when growing DWC. The trio should already have enough in it.

ProPheT 216 said:

View attachment 5158704

Dosent even look like weed. Um what kind of ph instrument do ypu use to check your ph. All your plants look like they are yellowing indicating some kind of issue taking up nutrients. They should have plenty to eat they need basicly very little at that stage. So we need to know more details. It's def something your doing

Click to expand...

That one definitely isn't cannabis. Looks like tarragon or some other herb. I see parsley cilantro and sage in the tent as well.

@Drop That Sound that's a good point, I just removed some water from the res. Thanks for the tip!
I added the calmag early because I wanted to start with a much lower concentration of GH Flora. On a previous grow I followed the "Basic Feed Chart" on GH's website, which calls for 4.2/3.8/3.0 on week 2 - that seemed to burn the hell out of the plants. Granted I was using tap water at the time and it had a baseline EC of 500-600, so that didn't help.

Per @OldMedUser's advice I removed the foil and added beads, but for now the little foam splints will have to stay until the leggy plants can stand on their own.

I'm glad you're telling me the trio should be enough for DWC - I've seen a lot of success stories from people with this same setup and no fancy additives. I'm hoping that by keeping it simple I have fewer variables to look at when problems arise, like right now. I think @ProPheT 216 was right about it being a PH issue. Today I've been lowering the PH gradually to avoid shocking them.

@xtsho Yep the one highlighted by Prophet is rosemary. I was just using it as a reference to see if there's something in that reservoir that's toxic to plants in general, even though rosemary has different needs than cannabis. In a second container I have only non-cannabis herbs and plants: cilantro, sage, basil, tomato, and a sunflower (which will have to move soon).

I removed one of the seedlings from the res and put it in a kratky pot just to use as a control, and I'm slowly lowering the PH in the res to see if that helps.

I figure it will take time for the plants to improve, so I'll post a photo in the coming days.

gwarf said:

@King Dude I'm hesitant to use soil in a net pot in DWC, the soil might crumble through into the reservoir. Right now I'm using rapid rooters in hydroton, I've heard others use the same setup so in theory it should work?

Click to expand...

I understand your concern. Although I'm fairly confident that a little bit of soil with coco coir wouldn't cause problems, I decided to suggest the Kangaroots liquid fertilizer at the end of my earlier comment.

Your setup seems just fine aside from Cal-Mag. Maybe there are some things that could be done differently, such as what other users mentioned about the water level. My main concern is that you're prioritizing calcium and magnesium over something as important as potassium. Coconut coir doesn't carry many minerals, and neither does distilled water.

ProPheT 216 said:

I say it's ph. No reason they should not have enough nutrients. My ph pen probably show a totally different ballpark than yours. Do u have calibration packs or.fluid. see of it reads 4.0 and 7.0 accurate if u do

Click to expand...

The OP is using Cal-Mag with distilled water and coconut coir. The reason I believe that it's a nutrient problem is because calcium and magnesium seem to be the only nutrients in abundance at this time. I could be wrong, as I am not a hydroponics user, but I can't shake the feeling that something is missing.

They currently have 1ml/Gal of each of the GH Flora parts. I'll add 1ml/Gal more, I doubt that will burn them at this point.
EDIT: typo

@ProPheT 216 I took your advice and ordered an Apera AI209 PH kit. After searching the forums for info on PH testers, I see the cheapo Vivosun one I'm using is widely panned for its shit quality. And I'll rely more on my GH chemical test, I neglected it for a while because I assumed the digital meter couldn't have drifted very far.

@gwarf

You can't judge seedlings usually and slight imperfections or flaws will usually show no matter how perfect your environment is. Note each plants shortcomings and use it to weed out plants that are problematic or have potential for it. Clone good plants and grow photoperiod so you can repeat results and dial in particular plants using your notes.