This is a very common happenstance with small tomato plants. The general consensus as I understand it is that some purple color is normal in small plants, and normally it goes away once the plants are finally planted out.

Be careful about putting too much fertilizer on the tomatoes in an attempt to get rid of the purple. While they might not be absorbing much phosphorus now because the night temperatures are low, once the temperatures rise and all that phosphorus is in the soil, they may cook.

If the plants look otherwise healthy, it's best to leave them alone and allow them to do their thing until they're ready to be planted out.

This post was edited by galiana on Fri, Apr 26, 13 at 12:53

Agree. Common and normal. Lots of discussions here about it.

Over-feeding them is much more of a threat. Feeding just encourages more top growth and the root development is already having trouble supporting the top growth. At this stage it is root development that is important, not top growth.

Dave

Thank you both. I'll go back to watering with warmed up snow melt (65 to 70 degrees) that has no fertilizer in it. The potting mix has a very low content of fertilizer.

I'm hoping to switch to rain water by next week !

Yes, the most common cause of purple leaves and stems is lack of P, but fertilizing the plants directly via the roots isn't going to help. What you need to do is to spray the foliage, which avoids root uptake, which is the problem.

You can use dilute blue stuff, like MG or Peters and the like or use a few drops of liquid concentrated fish or seaweed emulsion in some water.

I don't do anything b'c I know that the plants will grow out of it, but for many, just the sight of those purple plants is cause for concern.

Spraying the foliage works, and it will green up the plants, but only b/c you're bypassing root uptake, which is the major problem and it's worse if the temps are too low and temps alone can also do it.

Carolyn