That is why you should go with bok choi, which is very quick, specially
a certain hybrid which is rated at 45 days. Collards in August is too
late. Kale might make it. As Gary said, rapini will definitely make it.
As for all greens, quick growth follows plenty of water and frequent
high-N fertilizing. All of them like a higher pH than garlic. I keep
some wood ash from the winter into august so I can start the last fall
greens properly.