Deadheading / pruning off the dead blooms...
This does help with more repeat blooming as you already found out when you pruned alittle...

I do not use much fertilizer so I'll let someone else help you with that...

Roses are pigs when it comes to food. They like the stuff. Not too much all at once, but in regular, small applications, preferably. And they usually don't give a hoot if it was the expensive name-brand stuff or some cheap knock-off that was on sale when you happened to walk by it. And they also don't care if it was labeled "organic" or not.

So go for it. Feed them, give them enough water and sunlight and they will bloom.

kstrong is right. Even in the best soils, repeat blooming roses will need some nitrogen added every year. In poor soils, most nutrients need to be supplied each year as fertilizer. The yards of cane and hundred large flowers that you remove each year contain quite a bit of nutrients that must be replaced if the rose is to continue growing and blooming at that rate. The same is true of any fast-growing plant with limited root-run that gets a lot of pruning.

Rose Tone fertilizer is one of many good choices--about a cup every two months for a 3'-4' rose.

But fertilizer is not everything. Extreme heat or a shortage of water can also cut into the amount and quality of bloom.

It's too hot for them (or most any rose) to have large flushes of large blooms. Deadhead and feed and you'll see a dramatic change in the fall. Most of my roses aren't even blooming right now, and the ones that are have smaller blooms. My BD has been blooming, but the blooms are a bit small.

Note, With BD, the first blooms in the spring are larger than you'd expect to see, enjoy them!

I do give them a shot of alfalfa tea in the spring and late summer, and bush is huge. I'll be trimming and another shot of the alfalfa soon for our fall bloom.