How long can I grow seedlings indoor?

If one plants tomato seedlings indoors under florescent lights to grow
twelve weeks before transplanting outside and the plants normally are
supposed to produce ripe fruit within 65-70 days, what happens to that
normal development? Are the plants stunted or adversely affected in
some way that hurts their production after they are transplanted
outdoors? Would it be better to limit the seedling period to eight
rather that twelve weeks? Thank you!

Dave & Group:

The days-to-harvest for tomatoes and other transplanted crops are given from the
date seedlings are transplanted into the garden, NOT from the date seeds are
planted in the nursery.

Depending on several factors, including amount of light and heat in the nursery,
and the temperatures IN THE GARDEN SOIL, tomatoes can be ready for transplanting
in the garden as early as 4 weeks or as late as 12 weeks after seeds are
planted.

Florescent lights are NOT ideal for growing seedlings, especially beyond the
first transplant.

Plants grown under florescent lights do not receive anything approaching actual
sunlight, and so will not grow as fast nor be as robust as those grown in
sunlight. And they must be "hardened off" or acclimated to actual sunlight and
outside conditions more carefully and slowly than if grown in a greenhouse that
more nearly replicates garden conditions.

I recommend anyone using Grow-Lights to take plants into the direct sunlight
whenever the temperatures are conducive, even if it's only for a couple of hours
each day.

Plants should be in the garden by the time they are 10-12" tall (usually 8 weeks
maximum), unless they have been transplanted into gallon containers. And when
they get that tall the stem needs to be supported with a small stake carefully
placed into the soil and tied to the stem.

Jim Kennard