Smaller is Better.

Scroll down a few posts and you'll see more info on when to start your seeds if growing your own transplants. I have peppers that are a week old,  I will plant more this week and the following week. Tomato seeds could be started in a week as well as broccoli, basils and other annual herbs. Starting transplants too early is okay if you just want to mess around and don't have high expectations of survival. Here is why smaller, younger plants are better:

1. stem strength: using a fan in your growing area helps - however it does not imitate wind swept driving rains that plants need to be ready for.
2. WIND damage is one of the main killers of young plants. The smaller the plant - the closer to the ground - less exposure. You can of course use various types of protections.
3. Weak plant tissue: Plants grown with a fan and under lights are still much weaker in cell structure than plants grown directly outside. Transplants should be 'hardened off,' 'toned' or transitioned (whatever you want to call it) for 5-7 days before being installed into the garden.  
4. Cut back on water during the hardening period (no - not till the point of death!)
5. Many of the vegetable crops can be subject to 'checking.' This is a disorder that can occur when young plants become too rootbound and are not transplanted up at the correct time. When the plant becomes 'checked' it basically stops growing or the growth is stunted. Doesn't mean it dies, it just doesn't grow!
6. Vine crops are easily damaged by winds. They are always best direct seeded. Sometimes I start some in peat pots, completely outside for best stem development, and bring in at night. I would not start them until May 1 or so. Small.........is better! Vine crops do not like the transplant process either.
7. I am always amazed at the folks that are excited to buy a tomato or pepper plant "with blossoms already on it!" Let me interpet that: the poor plant has been rootbound for so long, and fears it's life will soon be over, and fearing the end - it does what every plants does, it's only purpose in life to reproduce. So it starts the process. Until transplants are firmly established in your garden, you should remove any signs of bud/flower initiation, let mama grow before you expect babies!

Enough rambling for today. You can always put words in the search box on this page to find more info on this and other topics......3-4 yrs. worth.