The ones I have ready to go were autumn sown. There are some January sown ones too which are pretty big now. All in the unheated greenhouse. Some didn't survive it when it got really cold (on nights I forgot to put fleece on them) but most did."If" you decide to grow some sweetpeas in a row, you could try training them way exhibitors grow them. As single stemmed plants, removing all tendrils and shoots, which means you have to tie the plants in to the canes, growing them up to the top of the canes, then untying them and laying them horizontally along the bottom of the canes, ready to go up again.I tried it one year, interesting, a lot of work, but it kept the plants going for much longer. Exhibitors always sow their seed in the autumn and I am sure, have their own magical feeding program for maximum colour, size and number of flowers per stem. If you type in "growing exhibition sweetpeas" you will find a whole new world of info. covering growing sweetpeas. Interesting, even if you have no intention of showing the fruits of your labour at your local Horticultural Show.Good luck, enjoy and have fun.