Transplants vs. Direct Seeding

Should gardeners plant vegetable seeds directly into the ground or plant them in small pots first, then transplant them into the garden?  
Some vegetables need to be direct seeded, while others are best transplanted. But most vegetable plants do well either way.

In general, transplants are easier to care for.  They are usually started in a more controlled environment - a greenhouse or some type of sheltered area.  Here, the seedlings are better protected from soil diseases, especially when a sterile potting mix and clean pots are used. A greenhouse offers protection from insects, animals digging up the ground and environmental stresses like hot winds and cold temperatures.  In cooler areas, seeds can start in a warm  environment and later be transplanted outdoors. 

Yet from time to time transplanted vegetables suffer from transplant shock. When the seedlings are set into the ground, the roots are damaged in the process. Plant growth is delayed until the roots recover. 

Certain plants can regenerate new roots quickly and as a result transplant easily; they include broccoli, brussel sprouts, cabbage, lettuce and tomatoes. On the other hand, cauliflower, celery, eggplant, onion and peppers are slower to regenerate, but they can still be successfully transplanted. The cucurbits (cucumbers, melons, squash, etc.), legumes (beans and peas) and corn have even slower root redevelopment, but if root disturbance is kept at a minimum, they will do fine. 

Vegetables that have a taproot like beets, carrots and turnips should be direct seeded.  Transplanting these vegetables will cause deformations and undesirable lateral root development.