Something went wrong, please try again later. Invalid email Something went wrong, please try again later. Sign up to our free email alerts for the top daily stories sent straight to your e-mailSomething went wrong, please try again later. Monty Don, in his most recent gardening blog post, has revealed the essential plants that need trimming in September, alongside other crucial gardening duties for the month. By trimming your roses, you're creating the conditions for more robust growth and an enhanced flowering period next year.