Hi piantini - there is some debate as to whether it is an actual deficiency or just the seedlings inability to absorb the phos from the soil. I fall into the latter group. But most all agree that it is a transient problem, not harmful to the plant in the long run, normal in many varieties, common in many others, and that it goes away once the plant has a chance to mature.

Sometimes the cause is the temperature of the growing environment - too cool, sometimes it is stress from over-fertilization, and sometimes nothing more than the roots trying to catch up with the top growth. Either way, trying to correct it often just makes it worse by causing more stress for the plant.

But once the plants are in the garden and the weather stabilizes it disappears 99% of the time so don't worry about it too much, ok?

Enjoy your plants. ;)

Dave

Dave,

You are always so helpfull. thank you for your time to explain to me in details the nature of this problem. Now i know i dont have to panic next time that it happens.

I understand what you mean by sometimes making things worst when trying to do something about it. In this case, i was lucky enough to find out that what i did worked!. As soon as i repotted them into a bigger tray and provided compost they recover quite nicely. As the matter of fact the purple color is almost gone!.

My basement is heated so the temp stays mid 60s so the cool temp is not an issue. I do water them with warm water so that helps.

Also, i added aluminum foil to the bottom of the tray and all over the top of the lighting fixture, to reflect as much light as possible.

Now i have to figure out how i am going to grow the other 6 kinds of tomato plans in my 4' fluro light. I only have room for one more tray!. Wish me luck

Not only P defficiency gives such an effect but N and Mg too.