It's a good idea to get a soil test through your county ag extension service, cheap in most states but not available in California. For soils that have been fertilized for a few years, the test usually shows high phosphate and potash. Nitrogen, which does not persist in the soil, needs to be supplied every year. Epsom salts can be harmful if the soil is already high in Mg.

Your mix is very low in potassium and unnecessarily high in phosphate. Plants use 3 times as much nitrogen as phosphate. In most cases, rock phosphate and bone meal are a waste of money, and a great excess of phosphate can be harmful. Alfalfa is a well-balanced (3-1-2) organic fertilizer at one cup every two months of growing season. Double that for large plants.

I have to agree with Michael. I used bone meal and epsom salts for years because Gramma and Mom did. When I stopped using them I didn't see any difference on how the roses performed. And do get a soil test. It's worth the cost.

Here's a scientist who says that the idea that roses need high levels of phosphate is a myth. She concludes that non-agricultural soils generally have adequate amounts of phosphate, and the addition of excess phosphate fertilizer decreases mycorrhizal activity and overall soil health.

So additional phosphate is not only most likely and unnecessary expense it can have a negative effect.

Here is a link that might be useful: Phosphate and Roses

The same scientists says pretty much the same thing about bone meal.

Lots of interesting reading a myth debunking on the whole site...

Here is a link that might be useful: Bone meal

You should feed at LEAST two times during the growing season. Once in the spring and once again in August. Try this mix; 1/4 cup fish meal, 1 cup Alfalfa, one cup Milorganite per bush. I'm sure you're roses will be happy with this mix.

I use fish emulsion once per month - easy- natural -smelly- but the roses love it.