Tall Thistle Seeds (Cirsium altissimum) Quick Facts:
Host plant to Swamp Metalmarks and Painted Ladies
Nectar plant to Monarchs, Swallowtails, and many butterflies
Native to central, eastern, and southern US
Hardy in USDA zones 3-9
Full to partial sun
Moist to medium moist soil
Pinkish Purple flowers bloom late summer, usually in 2nd year
4-5 feet tall (sometimes much taller)
Seeds need 30 day cold stratification or fall sow
Space plants 18-24 inches apart
Not aggressive like non-native thistles
Host and Nectar Source
The Tall Thistle is one of the host plants to Swamp Metalmarks and Painted Ladies. It is a popular nectar plant as Black Swallowtails, Cabbage Whites, Chalcedon Checkerspots, Cloudless Sulphurs, Milbert’s Tortoiseshells, and Painted Ladies are among the butterflies who sip from the Tall Thistle blooms. A fairly recent (Takahashi, 2006) survey done in Nebraska discovered that the Tall Thistle feeds at least 74 different types of insects!
Growing Thistle from Seed
The Tall Thistle seeds require 30 day cold stratification or fall sowing. After stratification, plant the seeds at a depth of 1/8″. Keep the soil moist, but do not saturate. Once it is warm enough, germination occurs within 2-3 weeks. If starting inside, transplant the seedlings after your last frost date.
The Tall Thistle grows a low-to-the-ground leaf rosette in its first year. During the second year, tall stems emerge with crowning large purple flowers late in the summer, with the blooms lasting from 4-6 weeks. The late-season bloom schedule makes them utterly invaluable to Monarchs as they migrate to Mexico for the winter. Each individual plant produces 25-45 flowerheads–quite the eye-catching display!
Although the Tall Thistle is not aggressive, its many flowers make for successful self-seeding. Your beautiful pinkish-purple nectar cups have the ability to reseed and continue their butterfly nourishment! Tall Thistle seeds are much beloved by goldfinches–they eat as many seeds as they can gobble and use the down surrounding the seeds to line their nests.
Non-native thistles, which tend to spread invasively by rhizomes, have given the whole thistle family a very bad reputation. North American native thistles, however, are highly desirable–both for their value to pollinators and well-behaved growing habits. Planting native thistles (such as the Tall Thistle) can help curb the onslaught of non-natives. The insects that eat thistles actually cause more damage to the invasive non-native plants. The Tall Thistle grows naturally in overgrazed pastures and degraded prairies, helping to save these areas from becoming barren wasteland. It prefers moist but well-drained soils. The sunnier the site, the taller the thistle.