Globe thistle is a fast-growing, contemporary-looking flower with old-world qualities: Its spherical blue blooms are arresting in the summer border, but unlike some eye-catching flowers, globe thistle plants are drought tolerant, deer resistant, and an important source of nectar for butterflies and bees. While repellant to nibbling rabbits and deer, the spiny, spiky foliage also serves an important niche in the wildlife garden by providing food as a host plant for painted lady butterflies. In the fall, when the blooming time is over, globe thistles continue to provide textural interest with their attractive seed heads. Plant your globe thistle in May or June.
|Common Name||Globe thistle|
|Mature Size||2 to 5 feet|
|Sun Exposure||Full sun|
|Soil Type||Dry, shallow, or rocky|
|Soil pH||Acidic; 5.1 to 6.5|
|Flower Color||Blue, purple, and white|
|Hardiness Zones||USDA growing zones 3-9|
|Native Area||Central Asia; Southeastern and South central Europe|
Globe Thistle Care
Globe thistle makes a statement in a low maintenance garden. They are good middle or back of the border candidates for a xeriscape, as they need little or no supplemental irrigation. They need no tending except for some deadheading to prevent reseeding, if desired. When globe thistle plants fail, it's usually due to heavy clay soil, or wet conditions. Plants growing in dry, sandy soils may thrive to the point of invasiveness.
Globe thistle plants need a full day of sun to remain compact and bloom well. If used as part of a foundation border, plant them on the east or south side of the home.
Good drainage is important for healthy globe thistle plants. The plants tolerate dry and rocky soils. In areas with heavy clay, use raised beds to improve drainage or plant in containers.
The long taproot of globe thistle enables them to survive drought conditions. Water newly planted globe thistle weekly, in the first month to help them get established, then only water if plants show signs of drought stress, like browning of foliage.
Temperature and Humidity
Globe thistle plants thrive in hot, dry areas. In areas of high humidity, provide proper plant spacing and a position in full sun to prevent mildew.
No fertilizer is necessary for the globe thistle. Plants may flop in conditions of too much fertility and require staking.
Globe Thistle Varieties
'Arctic Glow': White blooms contrast with reddish stems and silver leaves in late summer.
'Vetch's Blue': Dark blue flowers contrast with curving grayish-silvery stems.
'Taplow Blue': Steely-blue flower heads sit atop leafy stems; this variety has 5-foot stalks that are perfect for the back of the border.
Cut away the spent flowers to add to dried flower arrangements, to prevent reseeding, and to encourage re-bloom. Cut dead plants down to ground level in late winter.
Propagating Globe Thistle
Although it's easy to make new globe thistle plants from seed, you can also propagate them by division. Wait until plants are at least three years old, at which time you should be able to see some new plantlets at the base of the mature plant. In the spring, separate these new plants with a sharp spade and replant. Wear gloves to protect your hands from the spines.
How to Grow Plant Thistle From Seed
Collect seed heads from globe thistle plants in the fall, and remove seeds. You can sow outdoors, where germination will occur naturally in the spring. If starting indoors, stratify seeds in the refrigerator for best germination. Use large cell packs to accommodate the long taproots that begin to form after germination.
Potting and Repotting Plant Thistle
Growing in containers is one way to control globe thistle plants when they exhibit invasive qualities. Plant them in combination with other xeriscape plants that add contrasting color and softer textures, like yarrow or lavender cotton. If you wish plants to return the next growing season, they should be at least two zones hardier than your area, to withstand the deep freezing that occurs in containers.
The long tap root of the globe thistle presents some potting and repotting challenges. It's best to choose a large pot for a permanent home for new globe thistle transplants. Choose a sandy loam or cactus potting soil for the plants. Repot only if plants need to be divided.
After your globe thistle has stopped blooming, cut to basal foliage and leave be till next season.
Insect pests take advantage of poor growing conditions for globe thistle, like wet spring weather. In this case, you may observe aphids or the four-lined plant bug. Cosmetic damage is minimal, and decreases as the weather warms, so spraying is not needed.