When Does Fireweed Bloom in Washington State?

Bloom Times

• In Washington state, fireweed shoots begin showing in the spring followed in one month by leaves. Blooms begin in June if spring temperatures are mild or in July if temperatures have been chilly. Fireweed continues blooming through August or September, releasing seeds beginning in August and continuing until the plants dies back with the first frost. It spreads quickly with underground rhizomes, or stems, and can be invasive in some areas.

Factors Affecting Blooms

• Although fireweed is one of the first plants to colonize an area after burns or clearcuts, it also needs soil fungi to thrive and produce flowers. Fireweed that appeared after the Mount St. Helens volcanic eruption in 1981 died without flowering because the heavy layer of ash meant the fungi were not available to help the plant get nutrients. The plant also might not flower every year at alpine elevations such as those of Mount Rainier or Mount Adams.

Soil and Sites

• Fireweed grows in a wide variety of soil types including those with either low or high amounts of organic matter and in those with acidic, alkaline or neutral pH levels. However, plants growing in highly acidic soil will produce fewer blooms. Fireweed grows in Washington's coniferous forests, in grasslands, below the tree line at high elevations and in low, swampy locations. It also blooms profusely by the sides of roads, close to train tracks and in abandoned fields.

Growing Fireweed

• Fireweed grows up to 6 feet tall and 1 foot wide in U.S. Department of Agriculture plant hardiness zones 2 through 9 and needs full sun to produce abundant blooms. It will also grow in lightly shaded areas but produce fewer plants and fewer blooms. It thrives with moderate watering; a deep soaking every two to three weeks is all it needs.