Seed or Seedling
Seed - the following are easy to grow from seed, or "direct seed", in your garden simply by following the instructions on the back of the seed packet. Also, Johnny's Selected Seeds is also a great resource for planting instructions. In our garden, seeding occurs in the garden beginning mid-April, weather depending.
Herbs: Basil, Chervil, Cilantro, Dill, Parsley
Veggies: Arugula, Beans, Carrot, Collard, Cucumber, Greens & Lettuces, Fennel, Kale, Melon, Pea, Parsnip, Potato (from potato not seeds, but direct into the ground), Radish, Spinach, Squash (butternut, acorn, etc), Swiss Chard, Turnip, Zucchini
Seedling - the following are best grown from a seedling, or "transplants", purchased from a local farm, farmers market, or garden center. These plants take much longer to mature than say, arugula, and in our short midwestern growing season they would not have enough time to grow to maturity. To get a head start, these seedlings are grown in greenhouses weeks before it's warm enough to plant outside.
Herbs: Celery, Lemon Balm, Mint, Oregano, Rosemary, Sage, Tarragon, Thyme
Veggies: Cabbage (could try direct seed), Eggplant, Kohlrabi (could try direct seed), Leek, Okra, Onion, Pepper, Shallot, Sweet Potato (from "slips"), Tomato
Annual or Perennial
Annual plants only grow for one season, thus need to be replanted each year.
Annual Fruit & Veg
Arugula, Bean, Beet, Carrot, Cucumber, Greens & Lettuces, Melon, Pea, Pepper, Radish, Squash (butternut, acorn, etc), Tomato, Zucchini
Basil, Chervil, Cilantro, Dill, Parsley, Rosemary (or bring your rosemary inside for the winter to keep it alive)
Perennial plants come back each year, so you plant them once and enjoy them for years.
Perennial Fruit & Veg
Asparagus, Blackberry, Blueberry, Raspberry, Rhubarb, Strawberry, all Fruit Trees that are hardy to your zone (for us - apple, cherry, pear, plum, sea berry, paw paw, persimmon, Chicago hardy fig, hardy kiwi)
Chives, Lemon Balm, Mint, Oregano, Sage, Tarragon, Thyme, Winter Savory
Reading a Seed Packet
Front of a packet from Johnny's Seeds
You will see the common name & latin name at the top.
It also shows the number of seeds per packet.
DAYS or DTM, as you will sometimes see is Days to Maturity, meaning when the plant will be ready to harvest.
This packet says you can harvest baby fennel at 50 days and full size fennel at 80 days. It's up to you.
GERM & DATE
This batch of seeds has a germination rate of 92%, which is great.
The seeds were tested on 12/19. This date is helpful to know if you keep seeds for multiple years. They don't last forever so look at your dates and if it's past a couple of years, try them, but you may need new seeds.
Back of a seed packet from Johnny's Seeds
There is a ton of good info on the back of seed packets, especially from Johnny's.
Look here for all the information you need regarding seed spacing, depth of seed and so on.
For example, it says for this fennel to plant 10 seeds/foot 1/4" deep and then thin seedlings to 6" apart. I don't like to thin, so I would just plant the seeds at 3-4" apart and let them grow like that.
This information on harvesting can be extremely helpful if you aren't exactly sure when your crop is ready to enjoy.