Eupatorium capillifolium

Dogfennel is an herbaceous perennial in the daisy family (Asteraceae) with finely dissected leaves that are very aromatic when crushed (an aroma that is unpleasant to some). Widely regarded as a weed in the Southeastern US, dogfennel is grown in perennial borders in the UK, and both the species and the cultivar ‘Elegant Feather’ have earned the Royal Horticultural Society’s Award of Garden Merit. The species epithet is Latin for “hair-like leaves.”

Dogfennel grows rapidly in moist but well-drained soils in full sun to part shade, although it does best with some afternoon shade in hot summer climates. It tolerates most soil types, including dry, sandy soils. Plants have good drought tolerance. North of USDA Zone 6, this plant is best given a thick winter mulch and planted in locations affording some protection from harsh winter conditions.

Dogfennel foliage is feathery and can sway gracefully in the wind in an ornamentally attractive manner. If you regard this plant as a weed, know that it spreads in the landscape by wind-blown seeds and spreading rhizomes, so it is important to prevent the plants from flowering. Seedlings emerge from spring through early autumn. Plants are difficult to remove, and if not removed completely with hand weeding, plants will resprout from broken stems. Dogfennel is managed by many broad-spectrum preemergence herbicides; however, herbicide efficacy rankings for this species are based on limited experimental data. 

If you embrace dogfennel as an ornamental, grow it in perennial borders in native, cottage, butterfly, rock or rain gardens

Diseases, Insects, and Other Plant Problems: No serious insect or disease problems. However, you should watch for powdery mildew, aphids, slugs and leaf miner.