whether to fertilize or not depends on your climatic zone. Here it is often advised to fertilize in early september, after the heat of the summer, to get a rich autumn flush. Roses stops around november, some even december (like the fairy, very late bloomer, and mutabilis, which blooms until there is a ray of sun).
If you live in a cold area, then maybe it is not a good choice. As a rule of thumb you could consider to fertilize early september in z8, and subract one month per zone, like august if in z7, july if in z6, or october if in z10. Well, just as a rule of thumb: you know your climate far better than anyone else!

I would amend the soil with a good fertilizer, personally I use nitrophoska gold as it is very balanced, but there are other valid products. In your case, I would look for something richer in nitrogen and phosphor, should not be difficult to find, really. BTW usually phosphor is needed in small amounts, and nitrogen is sold here in large packs, low price. You throw it once or twice a year, that's more than enough. Rain slowly melts it (it is shaped like tiny spheres) and it gets into the ground.

1. Even if you live in the upstate, your roses still have around three months to grow, bloom, and store carbs for next year..

2. You don't really expect serious winter damage (beyond loss of soft new growth) in SC, so far as I know.

3. Since there haven't been scientific trials, no one really knows whether withholding fertilizer in fall actually helps tender roses even in areas where winter damage occurs. You can't really make them stop growing and harden off. New growth will be lost anyway, and that doesn't make much difference,

I wouldn't hesitate to fertilize well into September. If phosphorus is low, I would use manufactured fertilizer such as Miracle Gro or cheap 10-10-10, because P in bone meal is not available to plants. Additionally, you need to build up the base of P in the soil for the long term. Bone meal 0-15-0 is fine for this, or superphosphate. For new plants, dig 1 cup of bone meal into a square yard of topsoil. For established plants, apply the same amount in multiple drills around the drip line at a depth of 3-6 inches. If you use triple superphosphate 0-45-0, use 1/3 cup. I would wait for dormancy before disturbing the roots. The phosphate willl stay where you put it for years, except in pure sand.

Nitrogen needs to be applied regularly. You could use 1/4 cup blood meal or 1 TB urea or plain Turf Builder about once a month.

Or for routine fertilizing, a mixed organic fertilizer such as Espoma Plant Tone is very effective. These contain all the nutrients.

About pH-- did the reading of 7.5 come from a reputable source? If so, apply 1 cup of sulfur per square yard. It will take a year to work. Meanwhile, you can expect iron deficiency symptoms on some roses, pale new growth with greener veins.

Did you have your soil tested at the Clemson extension
center where you live? If you did, they will tell you
exactly what and how much of it to add to the soil.
We still have a good three months of growing season
left, so I'd do it now. Now is also the time to fertilize for the fall bloom. If you live anywhere near the midlands, there is a feed&seed store in Gilbert that
sells a generic version of mills magic mix that you can
buy in 50 lb. bags.

Thanks for the replies. I bought a Luster Leaf test kit. From what I heard they're fairly accurate. I may have screwed up the pH part. They recommended using distilled water, which I didn't have at the time so I just used tap water. I don't have a Clemson extension very convenient. I'll probably make the trip to one next spring for an official test though.

Well then, don't apply sulfur until you have a trustworthy pH reading-- unless you are seeing lots of iron deficiency symptoms. In that case you might apply up to 1/2 cup of sulfur to clay soil or 1/4 to sandy soil.

Test-tube pH tests can be hard to interpret, at least for me. Litmus paper or the Rapi-Test meter are OK.

Probably a complete reliable professional soil test would have been cheaper than the test kit.

Most every county in SC has a soil testing service that
usually costs around $5-10. They send the soil to the Clemson soil testing lab, which in turn, sends you a detailed analysis of your soil and what it needs to grow
whatever you're growing. You can still add fertilizer, such
as mills, now and then amend the soil later. I'd get the soil test done now.