Black spot in soil
Thank you for your question. There are two diseases both called "black spot." Do you know which has infected your roses? The rarer of the two is a bacterial infection, described here: https://pnwhandbooks.org/plantdisease/host-disease/rose-rosa-spp-hybrids-bacterial-leaf-spot-blast
The second and more common disease is caused by a fungus, and described here: https://pnwhandbooks.org/plantdisease/host-disease/rose-rosa-spp-hybrids-black-spot
Assuming yours is fungal in origin, the spores overwinter, not in the soil, but on live and dead plant tissue. That is why raking up dead leaves and branches, and pruning off diseased tissue is important. If your plants have this fungus, and you want to replace them, replace with rose varieties that are resistant to the fungus, as wuggested in the article. BTW, if you choose to use a fungicide, only those with (H) are available for homeowner's use. Hope this is helpful. Good luck!