I was told there was a perennial version, Lathyrus vernus, but in looking it up I find conflicting information. Some say it is a vining climber, like the annual, others that it is a low growing plant. Has anyone grown it that can give us the straight dope? Does it have worthwhile flowers?
Yes, there is a perennial version, mine is a vigorous climber that comes back bigger and better every year. Flowers are varying shades of pink and white. They take a few years to really get established, but they're worth the wait. It blooms for weeks and weeks with virtually no care, just needs a trellis to climb on.
Lathyrus vernus is a little spring pea, or vetch, and never gets more than 18 inches tall. It has no appreciable scent. It is very cute and easy to grow from seed, which cannot be sent to California due to invasive potential. It bears very little resemblance to sweet peas.
The perennial sweet pea has no scent. Sorry- it was a disappointment to me too.
I always grow sweet peas and my experience tells me that they should be innoculated with pea and bean innoculant (tiny bacteria) before planting. Mine really seem to like the organic vegetable fertilizer that I have started using. It smells so bad my husband won't let me keep it in the garage, but it really works!!
I use seed from "Renee's Garden" and start them early every year. They need to be well situated before the weather gets warm.
My Grandmother has one which is easily 60 years old now. It was planted about the time the house was built in the 1930's or 1940's. It grows in partial shade in well-drained sandy soil (near the shore of Lake Michigan) amended annually with compost. The flowers are smaller and less fragrant than annual varieties, colored pale pink to lavender. The plant could grow to 10 feet a year with a bit more care. Even so, it's lovely and mildly fragrant with the classic sweet pea scent. Wish I could tell you the variety, but I'm sure that information is lost by now.
In England one of the more popular perennials is Lathyrus latifolius - The Everlasting Pea'. I've got the rose pink form. Last year it was great, flowering from July to September with plenty of blooms. It climbs well and reached to about 6ft up a trellis. Sadly no fragrance with this one either.
We had a cold winter with more snow than normal but the plant has reappeared and is about 12in and just starting to climb again.
I've also tried L. nervosus (Ansons Pea) but seem to have lost it over the winter - pity because it is reputed to be scented.
Thanks to all of you for your responses, I think I have got it straight now.
L. vernus is the low bushy perennial and L. latifolius is the vigorous climber. Although there are warnings about L.l. becoming an invasive weed in California, my Zone 6 is at the limit of its range so I don't think I will have any trouble in controlling volunteers.