Several weeks ago, I went to a free class at Molbak's on starting a cutting garden. It was taught by Sue Goetz from The Creative Gardener, and had lots of great info about specific flower varieties to choose and how to set up a flower garden that you can cut from all summer.
First, you want to choose a place for you flowers that gets full sun; in my case, it was as close to full sun as I can get! (i.e. The Front Hill) You want your garden to be in a place that you can cut flowers often, and not be concerned if it looks half empty all the time, for instance, not next to your front door. You want to have good soil, compost, and drainage- and somewhere that you can water often, because most flowers are not drought tolerant. You can directly seed most of them into the ground, usually after Mother's Day. Remember that the more you cut the full-grown flowers, the more they'll come back for their second round!
When you are choosing flowers for cutting, you want to get the long-stemmed variety. I really didn't think about this too much, since I always have short sweet peas, but if you want to arrange them in a vase, long stems are best! You want to make sure to pick your flowers at the peak time; in the morning, but after the dew dries... about 10 or 11 am.
Some particularly good flower choices, according to Sue:
Annuals: (flower the first year)
Cosmos: Pink ones last longer than other ones. You should cut them when they are very open, but they go to seed fast. (You could also leave a few to go to seed, saving yourself work next year!) Varieties: Celebration in Pink, Double Cosmos- Bonbon (almost looks like a peony)
Zinnias: One of the best long cut flowers. Varieties: Berry Basket or Crayon Mix from Renee's Garden
Bells of Ireland: Likes to be slightly dry, so plant on the edge of your garden. Smells a bit lemony (and looks really cool!
Poppies: Avoid the single-petal varieties because the petals will fall off right away. Reseed themselves easily, and you can plant them in the Fall for the following year. Varieties: "Peony" poppies
Bachelor Buttons: You can "meadow sow" this flower (i.e. sow lots of it in a large area). It reseeds well. Varieties: Black Magic, or Tall Blend
Gomphrenia/Globe Amaranth: Kind of like a Strawflower. Germination rates are pretty low, but it dries well. Variety: Strawberry Fields
Sunflowers: They will give you several flowers per season if you cut them. Try to grow smaller ones that will give you more flowers per stalk than the giant ones grown for seeds. Protect the seeds from hungry birds by using row cover when you first plant them. Varieties: Royal Flush or Cinnamon
Calendula: I've been seeing this herb around a lot lately; it's medicinal and also just an edible flower. It blooms all summer and seems like a great choice for your garden. Variety: Flashback
Snapdragons: Long standing color, very heat tolerant. Will come back after you cut them. You want the tops to not be open when you pick them, so that they continue to open inside. Varieties: Ribbon Series, Tall/Maximum Blend
Nasturtium: Edible, attracts a lot of aphids (but also pollinators). I like the seeds because they look like brains. :) Varieties: Alaska hybrid, Cherries Jubilee, Creamsicle
Statice: Looks like Dandelion when it first comes up, so don't pull it! Likes dry parts of the garden and dries well.
Larkspur: Also referred to as "early Delphinium". You can plant it now, at the end of March. It has very long flowers and likes to be on the dry side. Varieties: Sublime Blend, Giant Imperial
Lemon Gem Marigold: Edible, nice fragrance, and long-lasting color. Brings lots of pollinators!
Nigella: Really cool striped seed pods after it is finished flowering. Some people grow it just for the seed pods. You can save the seeds for next year's plants, just wait until you hear them rattling around inside the pod. Variety: Persian Violet (the kind I planted this year)
(sow this year for flowers next season and continuing for years)
Liatris or Gayfeather: Pink bottle-brush flower. You can meadow sow it. Really pretty!
Columbine: I know for a fact this comes back because I have some that leapt into a pot from my parents' house and returns every year. Put out in the Fall, sometimes flowers more the first year, but it will self-seed for sure. Varieties: Black Barlow
Echinacea or Purple Coneflower: Bees love this! Don't get a hybrid variety of this, because they are not tall enough for cutting. Varieties: Magnus, Ruby Star
Lupine: Deer-resistant Variety: Russell Blend (I think after 4+ pages of notes here, I was starting to get tired of writing.)
Foxglove: Will grow in the shade, sometimes out of nowhere (and as tall as me!) but poisonous to animals- so take care if you have pets.
Sea Holly or Eryngium: This was one of the coolest flowers, so I saved it for last. Thistle-looking plant. Start it now, it will be best in the second or third year.