I come to you with an urgent cry for help. Last week, I transplanted my three week old tomato seedlings into larger pots. I fertilized them with a half strength fertilizer, and now some of them are falling ill!
I have been starting tomatoes for a few years now, and I am stumped. I have no idea what went wrong.
Here is some info about how they are being grown.
Soil substrate: Coir seed starting mix (Burpee Brand mixed with coir from a compressed block)
Location: East Facing Window (Under florescent bulbs)
When I transplanted them last week, that was the last time they were watered. They are usually only watered once a week. It seems random the ones that are affected. I am not seeing a correlation between varieties, old or new cups, or which lights they are under. Most have a dry soil surface but some have slight moisture (both dry and moist ones are affected). There is no evidence of spider mites or fungus gnats.
The intense purple would indicate a phosphorus deficiency and the curled leaves would indicate a temperature problem. Neither of these issues seem to be a good answer though (because they were fertalized and have consistent temperatures). On some of the seemingly healthy plants the leaves fall off with a slight touch.
This is so sad, I hate to see my plants suffering! If I am doing something wrong, how do I fix it!
Is it possible they are getting a chill from being too close to a window at night?
Could the soil be a bit dry? I water mine on demand whenever the soil looks or feels dry.
I fertilized them with a half strength fertilizer, and now some of them are falling ill!
I've never used any sort of fertiliser on tomato seedlings before so I can't help you there. I don't want my tomatoes to grow too fast before they are planted out otherwise, they will get root bound and I will have to repot them before it's warm enough to plant them out. A good soil will have plenty of nutrients for the few weeks that the tomatoes are indoors. I also noticed (as my grandfather was a huge fan of 'better living through chemistry') that fertilised seedlings (organic or otherwise) suffer much more shock when they get planted out than ones that were made to live on their wits. As they are, my seedlings grow pretty fast anyway. Too fast this year as spring is almost 6 weeks late.
When I plant the tomatoes out, I give their hole a generous helping of manure and they take off.
I'm also wondering about the seed. Are they all from the same source? Is this a source you trust? I once got some tomato seeds from an exchange. It turns out they weren't fermented prior to drying and they had a disease which spread to my entire tomato crop. I had to pull up the entire year's worth of tomatoes. It was similar to yours symptoms, only a little less purple.