PlantFiles: Yellow Starthistle, Golden Starthistle, Yellow Cockspur, St. Barnaby's Thistle Centaurea solstitialis
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Height: 36-48 in. (90-120 cm) 4-6 ft. (1.2-1.8 m) 6-8 ft. (1.8-2.4 m)
Spacing: 36-48 in. (90-120 cm)
Hardiness: Not Applicable
Sun Exposure: Full Sun
Danger: Parts of plant are poisonous if ingested Plant has spines or sharp edges; use extreme caution when handling
Bloom Color: Gold (Yellow-Orange)
Bloom Time: Mid Summer Late Summer/Early Fall Mid Fall
Foliage: Herbaceous
Other details: May be a noxious weed or invasive This plant is attractive to bees, butterflies and/or birds Average Water Needs; Water regularly; do not overwater Self-sows freely; deadhead if you do not want volunteer seedlings next season
Soil pH requirements: 6.1 to 6.5 (mildly acidic) 6.6 to 7.5 (neutral) 7.6 to 7.8 (mildly alkaline) 7.9 to 8.5 (alkaline)
Propagation Methods: From seed; direct sow outdoors in fall From seed; winter sow in vented containers, coldframe or unheated greenhouse From seed; stratify if sowing indoors From seed; direct sow after last frost
Seed Collecting: Allow seedheads to dry on plants; remove and collect seeds Properly cleaned, seed can be successfully stored
On Apr 1, 2007, Joan from Belfield, ND (Zone 4a) wrote:
This plant is listed on the North Dakota invasive/troublesome list and this information is being distributed in a guide developed by the ND Weed Control Association and other agencies.
Plant Features
Winter annual or biennial, up to 3 feet tall
Single yellow flowers on the end of branches
Flower heads have long, straw-colored spine-like bracts arranged star-like
Small stiff hairs give plants a grayish look
Long taproot
Spreads by seed only
May germinate in fall as a rosette (dandelion-like) and resume growth in the following spring
Distribution
First introduced in North Dakota via contaminated grass seed. All known areas have been eradicated
Interesting Facts
If ingested, causes lethal neurological disorder in horses known as chewing disease
Actually a knapweed, not a thistle
Produces a toxin that inhibits other plant growth (allelopathic)
Most abundant noxious weed in California (infests over 14 million acres)
On Dec 19, 2006, frostweed from Josephine, Arlington, TX (Zone 8a) wrote:
Yellow Starthistle, Golden Starthistle, Yellow Cockspur, St. Barnaby's Thistle Centaurea solstitialis is naturalized in Texas and other States and is considered an invasive plant in Texas.
I can't believe this showed up on a gardening site. A particularly obnoxious weed with little ornamental value. A severe problem in much of California, and hard to manage. Infests thousands of acres of rangeland; seems to suppress native vegetation. Seeds profusely; seeds will survive for years in the soil. The foliage grows very slow at first; while other plants are growing leaves, this one grows a long tap root straight down. By the the time most wildland foliage in my native foothills have browned-up in summer, the star thistle begins to bolt upward, gathering moisture from deep inside the soil. Toxic to horses. Nothing positive to say about this nasty plant.
On Nov 25, 2004, caron from Woodland Park, CO (Zone 4b) wrote:
Colorado Class A Noxious Weed. Mandatory eradication.
All locations of this plant in Colorado should be immediately reported to the Colorado Department of Agriculture.
On Jan 24, 2003, Terry from Murfreesboro, TN (Zone 7a) wrote:
A serious noxious weed, especially in the Northwest (U.S.) This thistle contains compouonds that produces chewing disease in horses, a permanent and fatal disease (the toxic effects build up over time when animals are allowed to graze infestested pastures.)
On the other hand, high quality honey is produced by bees foraging on these plants.
Gardeners are not encouraged to cultivate this plant.
