For asters to be nice and full in the fall, you must cut them back now. My rule of thumb is to cut them back twice, but never after the 4th of July. This year I just did them about 4 days ago, so I think that will be it for this year, I won’t have time to cut them again, or they won’t bloom until October. Here’s a photo of my tall New England asters behind the lavender bearded iris (which I just planted last fall to hide the aster’s lower foliage, which gets a fugus every year. I try to control it with a garlic oil spray, which does help, but the lower leaves still turn brown). The photo below is when I am half way done cutting them back, the front has been cut, the back is still tall. The last step will be to put a grow through system in. Mine have gotten too big for store bought grow-through hoops, so I put 4 stakes around them and criss-cross some green string around and through them.