That is indeed correct. You need a container at least 18 inches tall; a half barrel is ideal. They branch freely, too, so don't put in too many too close to one another or you will end up either thinning too many out; or lose them due to lack of nutrition which is a waste of your seed. The secret to great sweet peas is allowing them a good deep, cool, root run. They cannot do that in a cramped space. Plant them in rich soil, but do not add new compost immediately before planting. Well-rotted compost is the only type to use and it should be added about 3 weeks before planting and well mixed in with the soil. Of course, you should choose a free draining type of soil as sweet peas do not like their roots sodden. They should be moist, but not wet for very long.

I will say that sweet peas are not at their best in containers, however. They should be in the ground to develop in all their glory, and it is indeed that.

Not sure if sweet peas are the same as sugar snap peas but I grow Sugar snap peas in 5 gallon buckets, no problem.

Last years crop was 7 to 9 feet tall.
I had maybe 20 or so plants in each bucket.
5 gallon buckets are only 12 inches across by about 12 inches deep. About 1 cubic foot of container soil is needed.

I added a link with a photo of last years crop.
If you look carefully, you can see the vines are loaded with peas and they were awesome to eat.

Right now, I have 10 x 5 gallon buckets for this years crop. I added 6 more buckets over last years crop. The peas are only 3 or 4 inches tall at the moment here in western NC.

Here is a link that might be useful:

Sweet peas are really a vine and so need an extensive root system to support the vine. They won't thrive in a pot, I don't think.

No. Sweet peas are not the same as a snap pea or sugar pea and can get quite tall (8-10 feet). A five gallon container is not really large enough to get the best from them. I have grown in half barrels, and while they are nice enough, the ground is the best place for them.

There are dwarf sweet peas that are suitable for container gardening though. They can look quite well in a container or even a hanging pot; but they are not as spectacular as the Spencers or Grandifloras.

They generally need a soil slightly on the acidic side such as a pH of about 6.5 or so. This does not have to be exact by any means; a reasonable approach is to make the soil as nutritious (without burning them) as you can. You want a nice rich, well-draining soil that will feed them slowly throughout the growing season. If you wish to make your own (I am not familiar with Al's Mix) the goal is to have a loamy, light soil and by all means avoid a dense, clay one. Most of the time the packaged soil mixes do quite well. When I grow them in a barrel, I use Edna's Best or Whitney Farms mixes. If you want to add a bit of compost that is fine; but if you plan to grow them in a barrel year after year, you will have to top dress or replace the soil each year to avoid fertilising a lot througout the season. Sweet peas can be overfertilised; and do not use anything high in nitrogen as they are nitrogen-fixed and you will get stringy, rapid green growth of stems with lots and lots of visit from aphids! A tomato food works quite well midseason. If you have good soil, even in a barrel; fertilising should not be necessary until about midseason. Be sure not to fertilise until after the first flush of blooms in any case, but mid season is a good time as they are contained and maybe not getting enough nutrients after all the effort they put out and the unavailability of garden soil in a natural state.

They like their heads in the sun and their feet moist and cool. When your sweet peas start blooming, be sure to cut them frequently or they will go to seed thinking it is time to rest; the more you cut, the more you get!

The problem with sweet peas in a situation like that is the branching habit and the availability of sun for the flowers. The peas of lathyrus odoratus are NOT edible and can, in fact, be harmful if eaten. The goal of sweet peas is flowers; not food. Edible peas are a bit different in their branching and therefore can be a bit more crowded. Twenty peas to a pot in the case of lathyrus would defeat the purpose of growing them! I imagine you could do one to a pot. Try it; you will see what I mean in a hurry!

Thankyou very much hopflower.

I've grown stunning sweet peas in a 2x2' raised bed 10" deep, around my clothesline post. The soil below, that first year of the raised bed, was so different from the soil in the bed that it might as well have been a container. I recall planting 12 seeds or so, and the post became a mass of huge, scented, pink blooms.

"do not add new compost immediately before planting. Well-rotted compost is the only type to use"

All compost, by definition, is well-rotted.

Kristin

I have never grown these. I tried once years ago and the seeds didn't sprout. That was before I knew to nick them. I read that they bloom best when its cooler. So i got an early start. Some will go in the ground and some in a container. I also read somwhere that some sweet peas have no scent. I planted some knee highs and some even shorter. But the most are sweet pea old spice mixed colors from Ferry Morse. The seed pack says 10-12 feet. I hope these are the scented ones.Plus i hope they are transplant friendly. Thankyou for your help. Filix

Kristin: Oh my; I always seem to get an argument, don't I?
I should point out that there is such a thing as hot compost. There is a firm around where I live whose compost one year was a bit too hot and they sent warnings to people to be sure to age it a bit more before applying it. This is a professional supplier of compost which uses local grape waste and apple sludge mixed of course with other things. Compost does go through stages, you know.

Yes, of course your sweet peas would do well in that area. There is nothing wrong with those dimensions and you are keeping them from being water logged. But if you want spectacular ones, which is the point of growing them; you might consider what I tell you. I have been growing them for years.

Felix: most sweet peas do indeed have some scent. The perennial type do not; those that you see on the roadside that are fuchsia pink and purple or white, do not. The hybrids mostly do; but some are more strongly scented than others. I grow English ones which are superb for form and colour. I have put three stems in a vase on the table and had the room almost overpowered with scent with some varieties. There is a lot more to sweet peas than your local drugstore's litle packet. Should you be interested in these, which are developed for exhibition, please let me know. I will be glad to send you a few seeds to try out.

Oh yes, almost forgot felix: those Old Spice ones you mentioned are indeed very fragrant. They are the closest to the original wildflower and have only been moderately hybridised. They, too, will get tall.

If you are interested in form and colour and frill, then the others I mentioned that I grow are the ones to get. If it is scent you want; although you can get hybridised scented ones; the old fashioned (like yours) is the ticket. The colour selection is somewhat limited, however. Some gorgeous ones are Lady Grisel Hamilton, Dorothy Eckford, and Painted Lady; to name a few.

Thanks again hopflower. That makes me feel good that the ones I picked are good. And yes I would love to try some of your seeds. I have been growing some things for many years. But this year I have learned alot more. Sweet peas are one annual I realy wanted to do right this year. Since they like cooler weather I started them nice and early. When they sprout and get tall enough I will put them out. Maybe they will bloom in june? If its july or august, it gets pretty hot here. Somtimes in thr upper 90s. I think I read you can put them out six weeks before last frost? Thats where the container comes in handy. If it goes down in the 20s I could bring in the container. Have alot to learn. But having fun. Filix

They will start to flag if put out in hot sun. As the temperatures get anything over 90F for any length at all the flowers will wilt. They prefer cooler weather. They can also take a certain amount of frost once up high enough; and are not quite as delicate as they look.

I will be glad to send you some seeds should you be interested in them. Just email me and we can arrange it then.

Filix: Tried emailing you back but apparently your addy does not work.

Okay, filix. Got the new one and wrote back to you. Soon you should be planting new sweet peas seeds!

Many many thanks! Filix

I have a container 2' x 2' x 2' Much like the linked photo but square. I am wondering if I should put 2 or 4 heirloom Sweet Peas in it. I live in a dry area so I thought 4 would help hold humidity but may crowd roots. So them 2, but I want lush growth. Anyone have an opinion?