just keep covering them the nights you expect frost. unless you miss a night with a heavy, killing frost you should see a few more weeks to finish.
I'm confused about the 'flushing'. Are your plants in pots?. Outdoor plants don't often need flushing to finish. Flushing usually means flooding with 3x the volume of the bucket or grow bag with water to wash away accumulated mineral salts or to remedy an overdose of something.