Chamaenerion angustifolium

Chamaenerion angustifolium - fireweed

Chamaenerion is a genus of perennial herbs with 8 species, 2 of which occur in North America and the Pacific Northwest (FNA 2022). The two species include Chamaenerion angustifolium and Chamaenerion latifolium (dwarf fireweed). Chamaenerion angustifolium is much more common and is larger in stature than Chamaenerion latifolium, which is restricted to montane habitats.

Chamaenerion angustifolium is a valuable plant for native landscapes and restoration projects because of its ability to quickly grow in disturbed areas, its wide range of soil tolerance (can grow in moist soils except for constantly saturated soils), its ability to compete with exotic weeds and invasive species, its long flowering time, and its value to numerous pollinators. This species is available in the native plant trade but is not a widely used horticultural species, despite its potential. It has a somewhat aggressive growth habit and can spread vegetatively in areas quickly. It should be used in situations where this is an asset rather than a labiality.

Seed propagation

The fruits are a 4-10 cm long capsules that split open at maturity to reveal a few dozen to hundred tan to brown small seeds (~1 mm) with white floss-like fibers that are several times longer than the seed. Seeds are wind-dispersed and may reach heights of ~100 m which results in long distance dispersal (hundreds of kilometers) (Solbreck and Andersoon 1987). Collect fruit when capsules are splitting open or when split open upon the light application of pressure. Fruits may not have an obvious color change to indicate maturity but once fruits split open, the white wind-transporting tissue associated with the seed is readily visible.

Seeds readily germinate without pretreatments (are nondormant) and may prefer light for germination. Seeds are orthodox and can be stored for at least 4 months under ambient laboratory conditions (25 °C and low humidity). Seeds collected in the fall 2021 and sown mid-February 2022 began germinating by 7 days after sowing and by 1 month after sowing seedlings had 4 true leaves. The application of 1,000 ppm Gibberellic Acid did not improve germination. There was 5X more germination for seeds that were sown on top of potting mix (45% mulch, 25% peat moss, 20% pumice, 5% vermiculite and 5% perlite) compared to seeds that were light covered with potting mix so that the seeds were no longer visible. Seedlings have been noted volunteering in nearby pots immediately after dispersal, indicating seeds are non-dormant.

Division Propagation

Plants are easily propagated from divisions. Cut large portions tissue that contains shoots, rhizome, and root tissues with a serrated knife. Rhizomes can be dug up when dormant and propagated from divisions.

Production

Plants are easily and quickly produced in containers. Barerooted seedlings placed in 4-inch containers (3 seedlings per pot) during early April produced installation ready plants with firm rootballs 1 months after transplanting. Plants maintained an attractive appearance in pots for 3 months including producing numerous flowers and fruits after which pruning was necessary to maintain attractiveness. Plants were grown within a potting mix (45% mulch, 25% peat moss, 20% pumice, 5% vermiculite and 5% perlite) top dressed with fertilizer (1/8 tsp of 15-9-12 NPK) and placed in a full sun nursery production system located on the Portland State University campus in Portland, Oregon.