Yellowing leaves on 10-day-old seedlings

FrankFastHands · May 7, 2026

Hi everyone,

I’ve been growing for a while, and this year I decided to test a different soil mix. The current composition I’m using is:

85% peat moss + perlite, mixed 1:1
14% worm castings
1% vermiculite
1 tablespoon neem cake
1 tablespoon dolomitic lime

I let the soil “cook” for approximately 25 days, watering it with pH-adjusted water around 6.2. Before planting the seeds, I measured the runoff pH, and it was stable at 6.6.

I watered lightly with pH 6.2 water on the first day. After 10 days, once the soil was already dry, I watered again with pH 6.2 water and added BioBizz Fish Mix at 1/4 of the recommended dose for this stage.

About 5 days ago, I noticed a few fungus gnats flying around the root zone, so I set up yellow sticky traps and increased air circulation. I also added an extra layer of perlite on top of the soil, around 2 cm thick.

Today, I noticed the leaves are turning yellow, as shown in the photos.

Does anyone have any idea what might be causing this? And if so, what would be the best way to fix or manage the issue?

Setup:

Current pot size: 0.8 L
Light: 120 W LED
Average temperature over the last week: 26.4°C
Average relative humidity over the last week: 58%
Strains:
- 2x Special Queen — Royal Queen Seeds
- 2x Special Kush — Royal Queen Seeds
- 1x White Widow #1

Vick_Vinegar · May 7, 2026

Tbh those seedlings look like 5 days old so I'm not sure what's going on. I'd worry about keeping moisture levels adequate. 10 days without watering is just insanity. I water everything daily regardless from day 1.as wild pH and EC swings from 10 day drybacks don't do seedlings any good. Peat and perlite, even at lower ratios like 80:20 will hold over 25% air even when saturated so there's no need to wait 10 days to water.

This is when you want parameters as stable as possible and wild drybacks will do exactly the opposite of that.

I grow in peat, compost, perlite and castings and water daily from the get go to keep them as stable in moisture content, pH and EC as possible.

We are in medium with so much aggregate these days that this phobia of watering has to stop. I see a thousand cases of underwatering to every case of overwatering these days as everyone has some strange phobia of watering.

Peat or Coco by itself with no aggregate holds enough air to sustain healthy roots even when saturated.. add a ton of aggregate and there's really no need to give 2-3 day drybacks let alone 10 day drybacks at any stage.

Good rule of thumb. If you need to put more than 10-15% of the pots volume in water through the pot, you need to water more often. Your pots might be 800ml, but they are only 2/3 filled so more like 500ml. If you have to put more than 50-75ml through those pots, you need to water more often...not more in total, just more often to keep a healthily regulated pH, EC and rhizosphere.

ph and EC will swing drastically as the medium dries out as you are measuring while saturated. You want to avoid that heavy swing especially with young plants.

Vick_Vinegar · May 7, 2026

For example, these were 10 days old. I was watering them every morning and filling up the trays in the arvo and letting em sit in it, and those pots are three times the size of yours (7" pots). At the same temp and humidity. Only 15% perlite too.

Don't be scared to provide water.

Ninjadogma · May 7, 2026

FrankFastHands said:
Hi everyone,

I’ve been growing for a while, and this year I decided to test a different soil mix. The current composition I’m using is:

85% peat moss + perlite, mixed 1:1

14% worm castings

1% vermiculite

1 tablespoon neem cake

1 tablespoon dolomitic lime

I let the soil “cook” for approximately 25 days, watering it with pH-adjusted water around 6.2. Before planting the seeds, I measured the runoff pH, and it was stable at 6.6.

I watered lightly with pH 6.2 water on the first day. After 10 days, once the soil was already dry, I watered again with pH 6.2 water and added BioBizz Fish Mix at 1/4 of the recommended dose for this stage.

About 5 days ago, I noticed a few fungus gnats flying around the root zone, so I set up yellow sticky traps and increased air circulation. I also added an extra layer of perlite on top of the soil, around 2 cm thick.

Today, I noticed the leaves are turning yellow, as shown in the photos.

Does anyone have any idea what might be causing this? And if so, what would be the best way to fix or manage the issue?

Setup:

Current pot size: 0.8 L

Light: 120 W LED

Average temperature over the last week: 26.4°C

Average relative humidity over the last week: 58%

Strains:

2x Special Queen — Royal Queen Seeds

2x Special Kush — Royal Queen Seeds

1x White Widow #1

Might have let the soil cook too long. I'm thinking EWC comes online in about 7-10 days, will have continued to accumulate as the microbes do their thing, so at day 25 the soil might have been getting kinda hot if you didn't water it down. If you're going to overdo something, you can do it with a lot worse things than EWC. A better move next time... First off 14% is a little strong but still okay... But you want to get a plant in the dirt earlier than that, like after 7 days so that the plant grows with the nutrient release curve. That way it's feeding the plant as it releases and doesn't get a chance to build up.

For now you have a few options. Leave it be and let it push through some hot soil (if it's just ewc it might take a beating and not die); Move it out of the soil and take the penalty for disturbing the roots, and put it in a lighter blend; or do a deep watering on the pot, get some runoff, and then give it time to recover and die. I'd go with the latter myself.

greengrower73 · May 7, 2026

FrankFastHands said:
Hi everyone,

I’ve been growing for a while, and this year I decided to test a different soil mix. The current composition I’m using is:

85% peat moss + perlite, mixed 1:1

14% worm castings

1% vermiculite

1 tablespoon neem cake

1 tablespoon dolomitic lime

I let the soil “cook” for approximately 25 days, watering it with pH-adjusted water around 6.2. Before planting the seeds, I measured the runoff pH, and it was stable at 6.6.

I watered lightly with pH 6.2 water on the first day. After 10 days, once the soil was already dry, I watered again with pH 6.2 water and added BioBizz Fish Mix at 1/4 of the recommended dose for this stage.

About 5 days ago, I noticed a few fungus gnats flying around the root zone, so I set up yellow sticky traps and increased air circulation. I also added an extra layer of perlite on top of the soil, around 2 cm thick.

Today, I noticed the leaves are turning yellow, as shown in the photos.

Does anyone have any idea what might be causing this? And if so, what would be the best way to fix or manage the issue?

Setup:

Current pot size: 0.8 L

Light: 120 W LED

Average temperature over the last week: 26.4°C

Average relative humidity over the last week: 58%

Strains:

2x Special Queen — Royal Queen Seeds

2x Special Kush — Royal Queen Seeds

1x White Widow #1

I use peat based soil mixes and have for 30 years indoors, the key word there is mixes. Peat alone or with perlite is too acidic and needs buffering and a wicking agent Look at Promix for what it is composed of and try to mimic that if you don't have access to any peat based soils. Its recommended with Promix that you feed, water, feed, water. in 3 gal pots I fed once a week and watered once a week 1 gallon at a time. I now feed 24/7 in a different system

I don't ph anything, ever my water comes in around 7.3 and my nutes take care of the rest. With peat PH down being an acid can accumulate in the soil so you think you are phing to 6.2 but your roots maybe bathing in 5.2 or lower from accumulated acid that never gets washed away.

FrankFastHands · May 7, 2026

Vick_Vinegar said:
Tbh those seedlings look like 5 days old so I'm not sure what's going on. I'd worry about keeping moisture levels adequate. 10 days without watering is just insanity. I water everything daily regardless from day 1.as wild pH and EC swings from 10 day drybacks don't do seedlings any good. Peat and perlite, even at lower ratios like 80:20 will hold over 25% air even when saturated so there's no need to wait 10 days to water.

This is when you want parameters as stable as possible and wild drybacks will do exactly the opposite of that.

I grow in peat, compost, perlite and castings and water daily from the get go to keep them as stable in moisture content, pH and EC as possible.

We are in medium with so much aggregate these days that this phobia of watering has to stop. I see a thousand cases of underwatering to every case of overwatering these days as everyone has some strange phobia of watering.

Peat or Coco by itself with no aggregate holds enough air to sustain healthy roots even when saturated.. add a ton of aggregate and there's really no need to give 2-3 day drybacks let alone 10 day drybacks at any stage.

Good rule of thumb. If you need to put more than 10-15% of the pots volume in water through the pot, you need to water more often. Your pots might be 800ml, but they are only 2/3 filled so more like 500ml. If you have to put more than 50-75ml through those pots, you need to water more often...not more in total, just more often to keep a healthily regulated pH, EC and rhizosphere.

ph and EC will swing drastically as the medium dries out as you are measuring while saturated. You want to avoid that heavy swing especially with young plants.

I’m going to follow your advice, especially the rule of thumb about watering more frequently if I need to run more than 10–15% of the pot volume through the medium.
Just to better understand your approach, around what day do you usually start feeding seedlings with nutrients? And do you add dry amendments to your soil mix from the beginning, or do you rely more on liquid feeding later on?

FrankFastHands · May 7, 2026

Ninjadogma said:
Might have let the soil cook too long. I'm thinking EWC comes online in about 7-10 days, will have continued to accumulate as the microbes do their thing, so at day 25 the soil might have been getting kinda hot if you didn't water it down. If you're going to overdo something, you can do it with a lot worse things than EWC. A better move next time... First off 14% is a little strong but still okay... But you want to get a plant in the dirt earlier than that, like after 7 days so that the plant grows with the nutrient release curve. That way it's feeding the plant as it releases and doesn't get a chance to build up.

For now you have a few options. Leave it be and let it push through some hot soil (if it's just ewc it might take a beating and not die); Move it out of the soil and take the penalty for disturbing the roots, and put it in a lighter blend; or do a deep watering on the pot, get some runoff, and then give it time to recover and die. I'd go with the latter myself.

Thanks for the detailed explanation. That’s an interesting point.

My first thought was that it could be either a lack of nutrients or a watering/moisture issue, especially because the previous comment suggested that 10 days without watering could have caused unstable moisture, pH, and EC levels.

But your point about the soil possibly being a bit “hot” makes sense.

Based on how the seedlings look, I’m trying to understand the safest move now. Even if the issue is either underfeeding or overfeeding, could doing a deep watering with some runoff be harmful in any specific situation?

For example, could it make things worse if the real problem is underwatering, root stress, or lack of available nutrients? Or would a mild runoff mainly help stabilize the medium and reduce potential buildup?

Vick_Vinegar · May 7, 2026

FrankFastHands said:
I’m going to follow your advice, especially the rule of thumb about watering more frequently if I need to run more than 10–15% of the pot volume through the medium.
Just to better understand your approach, around what day do you usually start feeding seedlings with nutrients? And do you add dry amendments to your soil mix from the beginning, or do you rely more on liquid feeding later on?

Amendments here but I do add root roids (mykos, bacillus, trichoderma and kelp/algae at 1.5-0.5-3) weekly from week two onwards to the tap water and keep in neutral in pH.

The mix is about 20L peat, 10L Coco, 20L compost and 10L perlite. Theres about 10% total castings and insect frass added alongside about half a cup each Neem, alfalfa, soybean and kelp meal. About 2 cups palagonite and 2/3 cup gypsum. It's been recycled a few times and had a few random 6" pots of potting mix thrown in so fuck knows what's left in it haha.

If I do grow in plain peat or Coco with a bit of castings in it, I usually start to feed once I transplant into the final pot around week three. The castings is usually enough to get me to week three with some root roids. Without the castings and microbes I feed from the start.

I find it's not about putting more water through the potvand fully over watering, more about putting less in more often if you get my drift.ti keep the rhizosphere in a constantly viable state.

FrankFastHands · May 8, 2026

Vick_Vinegar said:
Amendments here but I do add root roids (mykos, bacillus, trichoderma and kelp/algae at 1.5-0.5-3) weekly from week two onwards to the tap water and keep in neutral in pH.

The mix is about 20L peat, 10L Coco, 20L compost and 10L perlite. Theres about 10% total castings and insect frass added alongside about half a cup each Neem, alfalfa, soybean and kelp meal. About 2 cups palagonite and 2/3 cup gypsum. It's been recycled a few times and had a few random 6" pots of potting mix thrown in so fuck knows what's left in it haha.

If I do grow in plain peat or Coco with a bit of castings in it, I usually start to feed once I transplant into the final pot around week three. The castings is usually enough to get me to week three with some root roids. Without the castings and microbes I feed from the start.

I find it's not about putting more water through the potvand fully over watering, more about putting less in more often if you get my drift.ti keep the rhizosphere in a constantly viable state.

Thanks a lot for the detailed explanation. That really helps.

I’ll observe them more carefully over the next few days. I’ll also focus on keeping the rhizosphere more stable and avoid adding too many things at once while they’re still this young.

Ninjadogma · May 8, 2026

FrankFastHands said:
Thanks for the detailed explanation. That’s an interesting point.

My first thought was that it could be either a lack of nutrients or a watering/moisture issue, especially because the previous comment suggested that 10 days without watering could have caused unstable moisture, pH, and EC levels.

But your point about the soil possibly being a bit “hot” makes sense.

Based on how the seedlings look, I’m trying to understand the safest move now. Even if the issue is either underfeeding or overfeeding, could doing a deep watering with some runoff be harmful in any specific situation?

For example, could it make things worse if the real problem is underwatering, root stress, or lack of available nutrients? Or would a mild runoff mainly help stabilize the medium and reduce potential buildup?

I offered up a couple options, and each one carries its own risk to the plant. If you pull it out of that dirt and put it into something milder, disturbing the young roots that are already under duress from a high EC could shock the plant and kill it. If you leave it be, your placing a wager that the blend will probably cause some damage but that it's not strong enough to kill it and it can push through the stress. Doing a deep watering could deprive the plant of essential oxygen for a prolonged period that puts it at risk of anaerobic crash. If you're at a good enough dryback point then watering it down is the best call but if it's been wet for a couple days you gotta make sure it gets air too... So that alone can dictate which move you make.

FrankFastHands · May 8, 2026

Ninjadogma said:
I offered up a couple options, and each one carries its own risk to the plant. If you pull it out of that dirt and put it into something milder, disturbing the young roots that are already under duress from a high EC could shock the plant and kill it. If you leave it be, your placing a wager that the blend will probably cause some damage but that it's not strong enough to kill it and it can push through the stress. Doing a deep watering could deprive the plant of essential oxygen for a prolonged period that puts it at risk of anaerobic crash. If you're at a good enough dryback point then watering it down is the best call but if it's been wet for a couple days you gotta make sure it gets air too... So that alone can dictate which move you make.

Yeah man, I get what you mean. It’s honestly hard to choose the right move here because every option has some risk, and there’s so much conflicting information online.

This is my first time growing in this kind of soil mix. I’ve always grown in a fully organic soil before, and I didn’t even measure pH back then and I had very good results. I decided to change things this time to test whether the plants would develop faster, but I’m realizing that this kind of medium requires a lot more control.

I just got home and the soil was dry, so I watered and measured the runoff pH, which came out at 6.2.

I’ll watch them more carefully now and see how they respond. I’m also adding a very low dose of fish extract/Fish Mix, about 1/8 of the recommended dose for this stage.

If they start improving, which I hope they do, I’ll come back here and update with what I did.

greengrower73 · May 9, 2026

Vick_Vinegar said:
Amendments here but I do add root roids (mykos, bacillus, trichoderma and kelp/algae at 1.5-0.5-3) weekly from week two onwards to the tap water and keep in neutral in pH.

The mix is about 20L peat, 10L Coco, 20L compost and 10L perlite. Theres about 10% total castings and insect frass added alongside about half a cup each Neem, alfalfa, soybean and kelp meal. About 2 cups palagonite and 2/3 cup gypsum. It's been recycled a few times and had a few random 6" pots of potting mix thrown in so fuck knows what's left in it haha.

If I do grow in plain peat or Coco with a bit of castings in it, I usually start to feed once I transplant into the final pot around week three. The castings is usually enough to get me to week three with some root roids. Without the castings and microbes I feed from the start.

I find it's not about putting more water through the potvand fully over watering, more about putting less in more often if you get my drift.ti keep the rhizosphere in a constantly viable state.

There is no such thing as over watering, you can water too often but you can't over water. You can give your plants 10 gallons of water at a time and as long as you let it dry back you'll be fine. Over watering is watering too often not too much all at once. Saturate your soil, let it dry back then saturate again

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Yellowing leaves on 10-day-old seedlings

Yellowing leaves on 10-day-old seedlings

FrankFastHands

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