I tried sweetpeas for my wedding back in 1995. unfortunately, we got very hot dry weather for a good 6 wks previously. I had a great tan for the day, but my SP couldn't handle it, even with lots of watering. I now know they had powdery mildew, but how I wish I had had the benefit of this forum and David's expertise back then.
Linzy, I think the Gypsophila is easier to grow. It survived that yr when I lost the SP,s. Try it anyway, you canresort to your florist friend after if you have no success. But listen to David. I always thought I was being hard enough on my sp, but have been positively cruel this yr, reading this. They germinated in 18-20*C in prop, then got slung out into GH for 2 days at 2-3C, but were hot in day, so uot to CF for a day a bit cooler, then out altogether. They were started a month ago. Last batch started in unheated conservatory lower daytime temps, but a degree warmer than GH at night. Germinated more slowly, but straight outside once I saw enough were showing shoots. all romping on, am taking notes to see which do best, but I think the later started, colder grown ones already look stronger, if obviously shorter. They should have shorter internodal lengths, I think, which may lead to more flowering shoots eventually, as more potential shoots per length of stem.
I grow tender fuchsias for standard 'trees', and deliberately grow them warm with less light, to get lengthening between the nodes in the first yr. This grows a long 'trunk' quickly, with few nodes that want to flower along the stem. In the second yr, once they have reached the height I want, I keep them much cooler, only frost free, and they grow much shorter shoots then, allowing me to build a very dense, heavily flowering head. I tnink that Davids principles do the same. Having said that, this winter has been so mild that my fuchsias never dropped their leaves, but it was just cold enough that I will struggle to get the long cuttings I need to start new standards from the mother plants, but the established standards will romp away earlier with short growth and early flowering. Indeed, my oldest are flowering already, I had to nip off many buds and 3 full flowers yesterday. The weather could foil your plans, but grow'em hard, as David instructs, and they should be short and strong to start with, but should offer more flowers, than any softly grown ones. I have never grown from an Autumn sowing, axcept for my wedding, the only yr I had a complete failure. But I am entirely sure that that was down to inexperience to some degree, and the weather to a greater degree. They are so easy for beginners most times, and with David's help, you are not a beginner. But follow his instructions to every letter. Soil prep (very important for a timed crop),sowing and planting out times, pest control., picking before the date. Don't allow even one pod to form on a plant.the flowers only last a few days. The more you pick, the more you get. I think David will tell you to remove every single bud on evrey plant until a few days before your big day. Then the plant will be screaming to reproduce, and should throw out flowers left, right, and centre, in a frenzy, hopefully just in time. But I'm not sure you can get enough to make the kind of display David showed you, by your date. If only for table displays mixed with other plants, it depends on how many tables, the size of the vases, the mixer plants to hold them up. I would grow plenty of complementary plants as well, so that the SP don't have to go so far. remember that the stems are slender with no leaves. It takes a lot to fill a narrow vase alone without fillers of some sort, and they don't last long in oasis. Take into account the amount of arrangements you need to make, and how late you can cut them to be fresh enough. If you are doing your flowers yourself, I would like to bet that you are