If you don't already have some, I'd try to get hold of a quality bloom fertilizer - preferably a water soluble one. The roots will uptake nutrients much quicker than with bone meal, which could take up to a month to degrade enough to even be useful. Bloom ferts have all kinds of N-P-K specs, depending on which product you buy... so try to find one with a higher phosphorus (P) content than Nitrogen/Potassium. And since you're seeing some yellowing already, I'd make sure that the fertilizer contains some Nitrogen, just much less than the other two.

Start light with the feedings, and work your way up slowly. You should see the yellowing subside, and the flowers grow larger & healthier.

Best of luck! :thumbsup: