Leaves Yellowing?

[RackitMan]

It is just about impossible to troubleshoot as I have four plants in identical soil, from the same seeds, same size pots, same watering schedule, same lights and environment, etc.

Two are bushy and nice and green and two are much smaller with yellowing, but not sagging or curling, leaves. The smaller ones are propped up to almost the same height as the larger ones.

They are 3.5 weeks old and received one weak fert treatment in water.

Any thoughts?

[stinkyattic]

It would help if you told us about their lights and environment and what the pot size actually is...Check out the sticky at the top of this section and if you can put up pics, that would be good too. If the 'bot tells you you do not have enough posts, upload a pic as your profile pic and let us know.

[RackitMan]

I read the sticky, but can't see how it can be a PH or deficiency or ... and only affect two of the plants.

Soil was mix of seedling starter and Supersoil. Water every 2-3 days. 24 hour light. Humidity is low and temp is warmer than optimum. Good air recirculation.

Pots are 5" (1 quart) and may need to be repotted soon, but if that was the problem, wouldn't the larger plants show root stress first?

Lights are 3 each 15 watt LED spotlights and 2 cool blue and 1 warm 26 watt CFLS. They are about 4-5" above the plants. Again, if it was light burn, the taller ones should exhibit stress first as I just raised the smaller ones.

The two larger are about 8" and the smaller ones are about 6" tall.

Can't do pics now, but may try later.

[stinkyattic]

Actual numbers on temps and humidity? Air flow? What does the bag of SuperSoil give for NPK? How did you mix the soil? Runoff pH of each pot? I feel like I am interrogating you, lol.

[RackitMan]

I understand your questioning and appreciate your attention, however this is a baby grow and I am a currently an unsophisticated grower with little test equipment. No PH tester.

Local outdoor humidity is 15%. I have several cups of water in the grow chamber. Temp is about 85F in the day and 75F at night. Best I can do under the conditions. Airflow is like 60 CFM in a very small area.

I will have to check the soil package later, but it is standard 40% Supersoil potting soil, 40% MG seed starter and 20% Vermiculite.

Again what does it matter if the NPK is off or not if two plants are very healthy and the same genetics while two are struggling?

Water is spring water. Did one feeding of 20-20-20 at 25% of recommended dilution. Will go back to plain water for a while.

No signs of pests or spots or splotching. Leaves appear more bleached than yellow.

For what it is worth, I was an electronic tech for 20 years and am very good at troubleshooting, but this has me puzzled as all the variables appear to be the same for all plants.

If the two smaller ones are female and the two larger ones are male, might they have different nutritional needs? That is the only thing I can come up with.

[stinkyattic]

I too am an experienced troubleshooter, both for plants and for chem lab analytical equipment. I know, too, that it pays off to answer the stupid questions ... You have called tech support, so be prepared to answer the age old question:

Is the device plugged in? Har har har...

It matters what the NPK is. Trust me. If you are using a pre-fertilized soil, irregularities in your mixing may have left pockets of 'hot' soil and pockets of unferted soil, and plants need their soil to be consistent.
Females and males don't have different nutritional needs, and even plants of different strains entirely would be unlikely to show different symptoms at this stage based solely on how heavy that strain feeds- you'd see that more in late flower.
Spring water- this is an unknown as well. Is it packaged for drinking? Drinking water often contains minerals and metals, including sodium, that are too harsh for young plants, and not good in any life stage. It would be worthwhile to also check its ph - the liquid indicator drops are only $7 for the small bottle. Generally, tap water is the way to go with your houseplants.
15% humidity outdoors plus transpiring plants plus cups of water- your %RH is probably just about perfect. Your temps are not outrageous, but nearer the lights there are likely to be 'hot spots' and plant metabolism grinds abruptly to a halt at 96'F. Some strains are more tolerant of heat than others, and high Si levels can help, but 85 is as high as you want to go for any length of time.
Light- low leaves that receive no light will eventually yellow and drop. If your light pattern is irregular, you could gain by turning and rearranging the plants periodically.
Bleaching- This does happen in high temps and is commonly seen on leaves that are quite close to a light- too close. But pictures are important to determine the cause, since different patterns mean different things.
Finally, the feeding of 20-20-20- hm, let's see... you actually gave them 5-5-5 and if they had at least 5 sets of adult leaves at the time, that was not an inappropriate dose unless the soil already came fertilized. It isn't ideally balanced for pot though, and you would do yourself a favor to hunt around for a fert with a higher first number for vegging. Do not use azalea or orchid food though, because the pH is buffered in the 5.5-6.5 range for acid loving plants.

As soon as you can post up a pic...

[the image reaper]

good stuff, Stinky :thumbsup: