The good news is you should have good drainage with all those rocks in your soil. Now you must improve the water holding capacity and fertility by digging a large hole (twice as big as the root ball on the new rose plant) and remove the rocks that are larger than a baseball. Next add compost to the soil that is left and use this mix of native soil and compost to fill in around the new rose plants. Add Osmocote slow release plant food to top one inch of soil. You will need to fertilize your rose plants every year even with the compost added. Roses are heavy feeders. If you also prune, water and grow in full sun, then yes, I can promise you a  rose garden this summer. Keep growing, Marianne Binetti