Here are my Capsicum chilies. There are a month and a half/two months old. For some reason, some are growing faster than others. The ones not growing much have leaves which turn yellow. After a few days, these leaves die, as you can see on the second picture.
They are under a window and I'm spraying them with water usually every morning and night.
What is happening? Is there anything I can do?
I am living in London, UK.
I'd reccomend checking out this link, as it has a lot of great information and helpful charts for different patterns of leaf yellowing.
It looks to me like you may be overwatering. While misting regularly is a great way to keep pests down, you also run the risk of waterlogging the soil and drowning your roots. One option is to let the soil dry out a little between waterings, so you can be sure that the roots get a chance to breathe. If you want to keep up your current misting cycle, you might consider adding some sand to the bottom of your pot, to allow for better drainage.
If you're confident that watering isn't a problem though, given that you say you have a few plants that are doing well, it is likely a nutrient imbalance. If you have the resources to test nutrients in your soil, that would be a great place to start. Find where the soil in your healthy plants differs from the soil of those loosing leaves, and you'll be well on your way to lots of happy, healthy chilies.
The exact same thing happened to me last year. I had made the mistake of burying the seeds too deep - most of the plants didn't even emerge, and those that did behaved exactly like yours. This year I bought the exact same brand of chili seeds, and pushed them very lightly into the soil. They are in the same position on my same desk at the same time of year, and they look like this:
The cotyledons appear to be exhausting their nitrogen reserves faster than usual. The soil may have lower nitrogen or higher potassium/calcium than is normal.
Either that, or there may be too much moisture, but that's just a guess (misting twice a day may be overkill unless your house is arid or has big fans going). Too much moisture is supposed to bring extra nitrogen to the plant; however, I have heard that overwatering can somehow cause yellowing.
If you have soft water, that might be why. Too much sodium or such might be the issue.
In my experience, watering chillies too much causes them to die. Seedlings are more sensitive, so there's less room for mistakes. If the soil is only slightly damp, then it's perfect. Once the seedlings get to the size you have shown, it's better to water at the bottom of the pot (in the saucer or plate at the bottom, whatever it is called), instead of watering them at the top. The water soaks up, making it just slightly damp, and this helps the roots to grow down looking for water. But not too much water.
Also, rain water is much better than tap water. When I don't have rain, I fill the watering jug or spray bottle from the tap, and let it stand open for a few hours before watering my chillies, so the chlorine etc. the municipality puts into the water evaporates out first.
They also need sunlight for as many hours of the day as possible, and heat. Is it possible to put them outside? It's spring in London now, so not sure if it's still going to snow or frost there, which would be bad, but otherwise, outside it much better than inside.
Another thought - did you transplant them into those pots, or did they germinate there? It's usually necessary to germinate in smaller trays and then transplant, and that's sometimes a risky business. It you mess with the roots too much when transplanting, they don't like it. Try to dig them out with their surrounding soil / seedling mix, so as to keep the roots as they are.
I've been growing chillies and tomatoes for about 25 years and wouldn't worry at all about it if it's only the first pair of leaves which is yellowing. In my experience the first leaves always turn yellow and drop off before the seedlings reach the stage where they need transplanting. If it happens with later leaves then a few possibilities:
Also I think sowing multiple seeds in one pot is fine. When the seedlings have a few pairs of leaves, maybe 2" high, carefully empty the pot out, break up the soil, and pot on the healthiest looking seedlings. It's not really any different from sowing the seed into a rectangular seed tray, just that you've sowing fewer seeds.
Too big of pots, too much soil to hold too much water and not enough light.
Starting seeds in anything larger than a 2 inch pot is asking for failure. Are you using real grow lights? Please explain in detail what those plants are getting...
Did you fertilize? Baby plants do not need fertilize but all plants we humans try to grow needs fertilizer, a balanced fertilizer. Compost is not at all fertilizer.
Your baby plants might still make it if you stop watering too much, they have truly the right amount of light and the right amount of hours of light. Are these to be planted out of doors? We need to talk about acclimating your starts to the out of doors or even a green house from this environment they know to have to change...well, thicken or thin their epidermis to effectively handle the new input of light.
Those pots are too big to be growing starts, seedlings. So easy to over water.
Hopefully you used potting soil that is cheap and sterilized and did not come with fertilizer or water holding gimmicks. Did you put rocks or gravel at the bottom of the soil above the drainage hole? Big big no no.
How warm is that room?
