Depends on if they need those nutrients in such high amounts. And maybe the timing of the bloom is being regulated by something other than nutrients.

There are two ways I know of to force Rud's to bloom early, and it may be too late to consider either of them.

One is cooling. BES especially can be forced by mild refrigeration. The plant senses stress and throws blooms in self defense.

The other is accelerating the day-length, by providing more light on a faster pace than Mother Nature is supplying. Rudbeckia's bloom is determined by the amount of light she receives each day. Unfortunately, it's probably too late to do this reliably. You'd need to have started a few weeks ago. If you have a way to provide light an hour earlier and an hour later each day, you might get some of the buds open, and that might help sell them. A few new flowers and a lot of buds is an inviting product. Keep in mind, your customers may be disappointed when they plant them out and have to wait longer than it appears for the rest of the buds to open.

If you can find a bloom somewhere, you can use that as your sample, and that will sell the ones in bud . Just a Thought-----------Upnortdareh

Thanks for the advice, I think I'll just print out a nice color sign and laminate it of one in bloom and hope for the best.
Hopefully at least one or two of them would be in bloom by then, they are just so close, I wondered if anything would bump them over the edge.
Personally, I don't like to buy flowers like that in bloom anyway because I think they transplant better before they get that far, but most people don't seem to have the imagination that I do for what a plant might look like later on.
Have you noticed it seems like every year people want their plants a little larger, farther along and more finished? (But of course they don't want to pay more! LOL)
Thanks for the help
Sandy