But the key is knowing which perennials benefit from pruning now – and which should be left until later. Cut back bearded iris, daylily, and blanket flower to prevent pests and refresh plants for fall. · 7 plants youll regret not pruning in september – dont neglect these post-summer trimming tasks whether it feels like the end of summer or the start of fall, september is the perfect time to trim plants to encourage continued, healthy growth. · with that in mind, i highlight seven plants to prune in september that might really need some tlc in the coming days or weeks. The reason for pruning them varies, but they all like to get a snip this month. But which plants should you cut back , and which ones prefer to be left alone until frost arrives? If you haven’t done so already, head out and give them attention, and add these trimming tasks to your late summer gardening checklist. By september , cooler nights have arrived, and in colder zones the first light frosts may already be showing up. · cutting back perennials in september is one of the most effective ways to prepare your garden for winter and ensure vigorous regrowth next spring. · prune wisteria, roses, and lavender in september to control growth and encourage healthier blooms. · in today’s article, let’s walk through a specially curated list of perennials you can trim in september to achieve a better flower show next spring. · we’ve gathered together a list of 11 summer-blooming plants you should cut back in september. Today, we’ll explore ten summer-flowering plants that thrive with september pruning. In some regions, the month of september usually means early fall.