There's no evidence whatever that applying excess phosphorus increases the number or size of flowers. It can, however, damage the soil by tying up iron and zinc. Commercial growers of cut roses fertilize in the NPK ratio of 3-1-2 or 2-1-2, because it is well established that roses use more nitrogen than anything else. I'd just give them plenty of water and normal fertilizer.

I hope your roses make a gorgeous show.

Exhibitors will prune their roses 6 to 8 weeks before a show. You want to do so in stages over 2 weeks so that you spread out the bloom time because they recycle at different rates. It helps if you've taken notes on how long they take to recycle on average. But I think if you prune now you should be in the right range for Sept. 16th. Don't just dead head though. Give them a light pruning to encourage new growth. I would fertilize them now and then again about 2 weeks before the show.

Thanks Michael and Seil . I think I will give them a treat of fish and seaweed fertilizer right now.

The growth cycle depends on the rose type. My Society is having it's show on 10/11. I have calculated the dates that we need to prune to be ready on that date. You can adjust it to your show date:

Types of Roses Pruning Date
Bourbons 55-60 8/17/14
English They are all different but figure 50-60 8/17/14
Floribundas 50-55 8/22/14
Hybrid Musks 55-60 8/17/14
Hybrid Perpetuals 60-65 8/12/14
Hybrid Rugosas 55-60 8/17/14
Hybrid Tea 45-55 8/22/14
Miniatures 35-40 9/1/14
Portlands 60-65 8/12/14
Teas 45-50 8/22/14

It is also recommended to stagger the pruning, do one half of the bush one week, and the other half the next week, to ensure that you will have the best chance of having blooms on that day. You can also cut blooms up to a week before and keep them in the fridge to extend their life. Some rose exhibitors have special floral refrigerators in their homes for this purpose, but a regular fridge will do. Good luck.

A regular frig will do, but not a frost free. Frost frees will dry out petals something horrible.

Also, the buds need to be kept at least ten inches from any freezer unit (some of our older frigs are 'that' old)

I put mine in a frost free and just misted them once in awhile. They did ok.

I put mine in the refrig with a plastic bag over the blooms. Some of my roses don't like to be refrigerated.

Excuse my ignorance, but I'm puzzled by the numbers: 55-60, etc.
Good tip re. misting while in frig. Some of mine ball up in the cold. I'll try misting, and the plastic bag too.

The numbers mean, prune that many days before the day on which you need to have flowers.