Short stems on my sweet peas.

We're trying to grow sweet peas for our daughter's wedding at the end of the month. We possibly planted them a bit early but as we hadn't grown sweetpeas before we didn't want to be too late. The plants have been flowering for about two weeks and in the first week they were fine with long straight stems, perfect for our plans. By picking them everyday, we thought we would be able to keep them going.

However, over the past few days, they have started to get shorter, twisted stems.

Has anybody any idea why this should be and any suggestions as to what to do? We're feeding them once a week, should we feed them more (or less)?

I've only noticed this when the plants flower later on in the season, so maybe a bit of dilute Miracle-Gro feed would help.

Thanks for the advice and comments, I'm not sure if I'm going to be able to make a difference now as the wedding is in three weeks. However, I think I will reduce/remove the tendrils to see if that puts more growth into the flowers. Otherwise we'll have to put up with short stems and change the vases