How to prune swamp sunflower

Chelsea chop in late May to early June; cut back after hard frost in autumn. Cut stems back by roughly half in late May–early June to reduce height and flopping. After autumn frost, cut all stems to 3–4 inches above ground level with sharp loppers or shears.

Once mid-season for height control; once annually post-frost for cleanup. Swamp Sunflower blooms late in the season (September–October) on tall stems. Cutting it back by half in early to mid-summer ('Chelsea chop') keeps plants more compact and delays flowering slightly. After frost kills the foliage, cut stems to the ground. Leave seed heads for overwintering birds if possible.

Cut stems back by roughly half in late May–early June to reduce height and flopping. After autumn frost, cut all stems to 3–4 inches above ground level with sharp loppers or shears.