Yes, I plant sweet peas almost every year, usually at one end or the other of one of my regular rows of peas. The major "problem" with them is the weather. They are kind of a gamble here. If it's a cool to average year, they are fine and can be very beautiful. If its a hot year, they may fizzle out prematurely without having many flowers. The other problem with them is critters. I have had them chewed up pretty badly by woodchucks or rabbits, but this doesn't seem to happen ever time, so I think there are other things that animals might prefer. The earlier you plant them, the better they seem to do -- sow as soon as the soil can be worked. As long as the summer isn't excessively hot (upper 80s and 90s), if you dead head them, they'll bloom quite a bit longer.

Lathyrus chloranthus. Joe

Here's what I do - it takes time, but way less energy than digging. Stockpile heavy corrugated cardboard (appliance and furniture boxes are great, but the grocery store is a good source also) and an organic mulch that you won't mind looking at for a growing season. (My personal choice is natural wood chips or shavings, but chopped leaves will work also. I avoid dyed mulch since it's hard to judge what has been camouflaged by the dye.) Mow the area really short or clip or hoe it to ground level. Cover the area with the cardboard with overlaps - no gaps at all, and cover the edges with something to weigh it down - bricks, heavy chunks of wood, etc. Cover the cardboard with at least 4 inches of mulch and water well to settle it. The combination of cardboard and mulch will smother your weeds and then will over time decompose to give you soil of wonderful quality. Wait a year to plant - and watch like a hawk during that year, pulling any tiny sprig of green that might emerge. Resist the temptation to plant now since gaps in the mulch will allow your persistent weeds to regrow. During the year you can plan how you will plant it. To get ideas, visit public gardens, wander around neighborhoods with gardens you like, go on garden tours, and visit nurseries over the course of the season, not just in spring. If you really need to plant, you can put out pots of annuals or even of perennials & shrubs hardy to 2 zones colder than you are (if the pots are frost-proof.) If you are planning vines for your fence, you can shop for or create your trellises. If you don't have an edging that discourages the lawn from entering your beds, you can do that also, either a cut edge or an edging that is buried to keep the grass in the lawn. So if you do this now, you can plant the bed next spring. Just pull aside the mulch, plant, and tuck back in without piling mulch against the stems. Since you will have chive and sweet peas seeds that may have survived, watch for them and pull immediately. Or spread corn gluten around the plants you put in - it's a natural discourager of seed sprouting, but won't affect your newly planted plants. I'd love to see an after photo when you've got it planted!

Producing seeds uses a lot of the plant's energy. This is one of the reasons you might not get mature seeds from cut flowers. The plant needs to be able to gather food while it is developing seeds, and the seedpod needs to remain attached to the parent plant until the seeds are fully developed. Don't want to start anything because people set their own standards for flower picking and seed gathering activities in places that are not their own; but municipal plantings, parks, arboretums, greenhouses, garden centers, other people's yards, etc. etc. shouldn't be regarded as a free for all. :-)