A NORTHERN ARIZONA HOMEOWNER'S GUIDE TO IDENTIFYING AND MANAGING INVASIVE PLANTS
Common name(s): Horehound, white horehound
Scientific name: Marrubium vulgare
Family: Mint family (Lamiaceae)
Reasons for concern: This plant forms large, dense monocultures, which have a very negative impact on native vegetation, wildlife, and pollinators. Its dense root system makes it very difficult to eradicate.
Botanical description: Can be upright like small shrub, or creeping. Entire plant has pungent/aromatic odor.
Leaves: Oval to circular. Opposite on stem. Grayish-green. Toothed (jagged) edges, located below flower whorl. Lower surface covered with white woolly hairs. Upper surface wrinkled or puckered. About 1 ½ inches long.
Stem(s): Up to 3 feet tall. Usually erect, 4-sided, with a somewhat woolly base.
Flowers: Tiny to ¼ inch long, white, growing in dense round clusters where leaf meets stem. Tubular. Blooms April through September.
Seeds: Each flower produces 4 dark brown nutlets, each containing one seed.
Roots: Taproot, branched, woody, with numerous fibrous lateral roots.
Native to: Europe
Where it grows: Desert, uplands, mountain, riparian. Along roadsides. Disturbed places. Elevation 2,000 to 8,000 feet.
Life cycle: Perennial
Reproduction: From seeds and spreading roots
Weedy characteristics: Can form dense monoculture stands over large areas, reducing native plant diversity. Seeds can remain viable up to 5 years.
Control strategies: Do not let them go to seed. Hand pull or dig out seedlings. Dig out more mature plants with the roots, but be careful not to disturb the soil too much. Step down any loose dirt to prevent seeds from finding a welcome environment to germinate. The roots make it very hard to eradicate. Repeatedly monitor previous infestations for new growth. You may need to consult a professional. Plant desirable native species to outcompete invasives.
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