Hi Mattiegroves and welome to Goy. Sorry to say this but you have been given a poisoned chalice! Trying to get sweet peas, or any other flower, to bloom for a particular day is a real challenge. The professional growers have all sorts of tricks they use to ensure flowers bloom when they are wanted from forcing them to holding them back in a refrigerated environment. Who ever has asked you to grow the flowers would be much better going to a florist and ordering them in, they will guarantee to supply for the day and you will not have the stress for several months before the day of trying to ensure that the perfect sweet peas are available. Good luck if you do have to go ahead they'll need to be sown in spring but as to varieties I can't help.

Yes, you would have to plant a farm's worth of land with different kinds of sweet peas to be sure of getting a goodly number at the right stage on the particular wedding day. Florists' suppliers have those resources, but home gardeners...not so much!

Whoever asked you to do this is very optimistic. Growing sweet peas for a special day would be tricky even for an experienced gardener, and they are usually in bloom in June and early July!

Well, if your sweet peas grow successfully, they should definitely still be in bloom in August (mine were still going strong in September) as long as you regularly pick them to force more blooms. But the problem with them is that, once picked, blooms only look their best for one day. This may not be a problem for you, but I thought I'd mention it, just in case you can't pick them on the day itself.

The other problem, in my experience, is that they're extremely susceptible to mildew, so bear this in mind also.

If you're still happy to go ahead, select varieties which have been awarded the RHS Award of Garden Merit (AGM). The seed packets will tell you which ones have it.

Yes, I must agree, I don't think having them in flower in August would be the biggest challenge....but keeping them alive for the wedding. And if you want any kind of impact you're going to need MASSES! Sow them every couple of weeks from March onwards if you haven't got them started already (mine are germinating in the greenhouse just now) . Give them heaps of manure in the compost/soil at the roots, nice deep root run, don't disturb the roots once they are established and keep watering and feeding. Don't forget to remove the tendrils, and tie the stems to supports. That way the energy goes in to producing more flowers. But getting straight stems is a challenge...and getting them long enough for a vase or bouquet. I grew some really lovely ones this year, including 'Duchy of Cambridge' and 'Spanish Dancer' but a lot depends on what colour(s) you want, and whether the perfume is very important. I always try to get ones with strong scent. If its only a small wedding and you just need a lovely natural scented and informal bouquet for the bride, then you'll be fine. Good luck though!