|Why start seeds in a small flat or container only to repot them to larger container? Why not just start seeds in a large container?|
|You are right, seeds could even be started directly in the garden to save all the bother of transplanting.
Generally the reason for starting them in containers is to extend the growing season. So you may start your tomatoes in pots indoors while it is still too cold to plant outside. Then when the weather improves you transplant your seedlings out into the garden.
There are several advantages of starting in flats or small pots rather than right into large pots. It is important to start seeds in sterile pots and sterile potting medium to protect them from disease. Later when they are less vulnerable you can transplant them into regular potting soil. So starting them in flats or small pots makes this easier and less expensive.
Another advantage is space savings. In addition, you can more easily keep them under close supervision in an optimal setting during the critical germination period. Also you don't waste sterile pots and sterile soil on seeds that don't germinate.
Light is also an important consideration. Many people have to use artificial light and they want to conserve space to get as many plants as possible under the light.
If you have plenty of room, light, sterile pots, sterile potting medium, and the diligence to watch over them all, you can save yourself time and energy, and your plants transplant shock by starting them in larger pots.