While you can easily buy seedlings ready to transplant into your garden from garden centers or home improvement stores like Lowe's or Home Depot, you will be limited in the varieties available. Additionally, some fall crops should be transplanted mid-summer, at which point many stores have stopped selling transplants.
It is easy and fun to grow your own! Below are some guides on starting your own seeds.
Planting Date Guidelines
Some plants like it cool and can tolerate a late spring frost. Some plants need the heat and sun of mid-summer. Some do best when they are sown directly into your plot, and others should be started indoors as transplants to give them a headstart. Below are some general guidelines for when to plant throughout the growing season!
Note that individual varieties of certain crops may be bred for different parts of the growing season. Seed packets have the best and most detailed information on where and how to plant.