Hi again, Carly
Actually I recommended 6X as a substitute for farmyard manure, but this was in respect of preparing the growing site in the autumn.
Prior to planting out at this time, I would just use good compost (preferably homemade) to prepare your beds, with the addition of bonemeal....when they start flowering, feed with a high potash feed.
Depending where you live we can start planting them out anytime now. Just keep an eye on the weather forecast and try to plant them out when we have a few frost-free nights....this is to enable to recover from the transplant before having to face cold weather again.
Btw, remember what I said earlier, they really don't like cold icy winds.
Glad you mentioned your daughters wedding. I'ts quite likely these autumn sown plants will have finished flowering by then (certainly past their best) But all is not lost, just sow some seed in situ now...these should be at their peak by late August and last through until the first frosts.