[Garethw]

About 4 weeks ago I planted some Tomato seeds in propagators, with John Innes Seed compost, on the window sills. The little seedlings poked through after about 5 days. A week or so later they just started to grow their proper leaves so I pricked them out and planted them in 3" biodegradable pots with John Innes No.1. 
Now, the tomatoes that have been pricked out seem to have a slower growth than the ones which are still in their original pots. Plus the leaves are going purple on their underside.
All the repotted seedlings are on a South facing window sill. The other, stronger looking ones are on a North facing window sill.

So, my questions are:-
a) Is the purple undersides anything to worry about?
b) Have I pricked them out too early? I.e is the JI No.1 too much for them at this stage?
c) Have they had too much sun? (We've had about 2 weeks of really good weather now)

Oh yes, they are all Gardener's Delight and from the same packet.

Thanks

Gareth

[gillie]

Purple undersides mean the seedlings are too cold, perhaps only at night.  They will not die but it will slow their growth and is a warning sign to get them in a warmer place.  You have not pricked them out too early, and if they were sun scorched they would go brown.

[Kleftiwallah]

Try and prick them out and transplant with as much soil at the roots as possible.  This lessens the shock to the plant as it has to search out with immature roots for moisture and food.   Cheers,   Tony