my butterfly weed is still blooming, so I plan to leave it until frost. However, they are very spindly. So, thinking about the spring, should I cut it back to the ground after the first frost? Should I keep cutting it during the growing season so it bushes out more. I have trouble cutting off blooms and it bloomed all summer.

cutting back perennials is always a tough decision while they are blooming, but most respond well to a little haircut from time to time during the growing season. If your butterfly weed is an asclepies variety, most are considered annual plants that reseed themselves. If its butterfly bush(buddleia) then this is a woody perennial that grows like a deciduous shrub and should be pruned heavy after it blooms inthe spring. If its an ascelpies you can cut it now or wait for Mother nature to take care of it