I thought I would post about what I was told was the normal care (i.e. without short-staffing), for the roses in this garden:
1. They are normally sprayed with fungicide once/week in the spring unless it has rained. If it has, the fungicide is reapplied regardless of the time elapsed. Later on in the summer, the number of times they are sprayed may lessen, depending on the weather (the St. Louis area is notoriously humid in summer).
2. They are fertilized once a month.
3. Winter care: The roses are all cut back to 12 inches (about 1/3 meter) and buried in mulch, then uncovered in the spring when the weather starts to warm up. If there is a late freeze (like there was this past spring - 2021 - they may need to be re-buried, depending on the variety and how hard it freezes.
4. The roses are regularly dead-headed.

I recently spoke to the only caretaker left for this garden. He is also responsible for several sections of the larger park around the garden. According to him, the garden used to have a team of caretakers (I know a couple of years ago I saw at least two people working there at once). Due to budget cuts in Alton, it is just down to him now, and he doesn't have time to properly care for it. He was only able to get to it once per week in the spring, and with the multiple rains, the fungicide was washed off. Before he could reapply it, black spot had taken over. In addition, he no longer has time to fertilize as much as was previously done. As a result, the garden has gone downhill this year.

Unfortunately, on a subsequent day when he was not present, I noticed one of the Betty Boop plants has what I suspect is rose rosette. If it does, and it affects most or all of the plants, I would not expect the garden to be replanted, considering the budget cuts already made in Alton. So, my advice is to go see it while it is there. Right now it is a good lesson in which roses can survive best without hand-holding and which ones cannot. Some of them are quite a surprise on both sides.