Plant globe thistle in May or June to achieve mid-summertime blooms that last throughout the fall. Then, when blooming concludes, globe thistle continues to provide textural interest with its attractive seed heads. Simply deadhead this plant to prevent reseeding if you want to keep its spread in check. Considered non-invasive (yet extremely prolific), this plant likes dry, nutrient-poor soil and can thrive in hot and dry environments. Globe thistle only fails when it’s planted in heavy clay soil or kept in wet conditions where its taproot becomes susceptible to rot.
Light
Globe thistle needs a full day (at least six hours) of sun to remain compact and bloom well. If used as part of a foundation border, plant it on the south or west side of the home. This plant will tolerate some morning or afternoon shade, but will grow leggy if shade conditions persist.
Soil
Ample drainage is imperative for the health of globe thistle. This plant likes dry, rocky, or loamy soil with an acidic pH of 5.5 to 7. If your landscape consists of heavy clay, try growing globe thistle in raised beds with amended soil to improve drainage. Alternatively, you can plant this flower in containers.
Water
Globe thistle’s long taproot enables the plant to survive even the harshest of drought conditions. Water newly planted globe thistle weekly during the first month to help the plant establish itself. Then, water only if the thistle shows signs of drought stress, like wilting and brown foliage.
Temperature and Humidity
Globe thistle plants thrive in warm, dry regions with ideal growing temperatures hovering around 65 F to 75 F, although this plant can tolerate hotter temperatures like those found in USDA zones 9 and 10. In areas of high humidity, provide proper plant spacing for airflow, and position the plant in full sun to dry out the soil and prevent mildew.
Fertilizer
Globe thistle, like its weedy cousins, likes nutrient-poor soil, making supplemental fertilization unnecessary. In nutrient-rich conditions, this plant may grow leggy and flop, requiring staking.
Types of Globe Thistle
Different varieties of cultivated globe thistle provide a varied look in the garden. Pair the blue globes of one variety with yellow daisies or rudbeckia for a contrasting color wheel scheme. White blooms work well combined with almost any annual or perennial. Here are a few gardener’s favorites:
Echinops sphaerocephalus ‘Arctic Glow’ lends a unique appearance with its white blooms, contrasting red stems, and silvery late-summer leaves. This variety grows on robust stalks with a mature height of 2 to 3 feet tall and rarely needs staking. Use it to add golf-ball-sized starry blooms to your garden. Echinops ritro ‘Vetch’s Blue’ has deep blue flowers, which blend nicely with its curved, silvery stems. The blooms on this variety appear as 1- to 1 1/2-inch globes on 30- to 36-inch stems. Its moderate height allows it to fit well in most areas of the garden. Echinops bannaticus ‘Taplow Blue’ has steely-blue flower heads with white tips that look like mini disco balls sitting atop muted gray-green leafy stems. This variety grows 5-foot stalks, making it the perfect addition to the back of a perennial garden.
Pruning
Globe thistle needs to be pruned only for aesthetic purposes and to encourage rebloom. Deadhead spent flowers and add them to dried flower arrangements. The act of deadheading prevents reseeding, keeping the plant’s growth in check and encouraging a re-bloom. You can also trim the basal leaves to promote another round of flowers. Occasionally, the flower heads become heavy, causing the plant to droop. If this happens, you can either stake the plant, or cut the flower in its prime for interior bouquets. Cut dead growth down to ground level in the late fall before winter sets in.
Propagating Globe Thistle
Globe thistle can be propagated by division for transplanting in another section of the garden or gifting. Wait until the plant is at least three years old, at which time you should be able to see new plantlets at its base. Here’s how to propagate globe thistle by division:
How to Grow Globe Thistle From Seed
Globe thistle can be propagated by seed easily. In fact, it will readily spread on its own if you don’t deadhead the flowers. Note though that the seeds of cultivars don’t necessarily produce plants with the same features as the parent plant. To propagate from seed, first, collect spent flowers in the fall by harvesting the seed head and removing the seeds. You can sow the seeds outdoors by planting them in your garden bed in the fall. After the first spring frost, water your bed until germination occurs. To start seeds inside, you’ll first need to stratify them by placing them in a moist seed starting mixture and putting them in the refrigerator for a few weeks. Sow seeds indoors two months before the last frost by filling a seed tray with seed starting mix, dispersing the seed, covering them lightly with soil, and misting the soil. Cover the tray with plastic and locate it in a sunny window where you can maintain 70 F temperatures. Mist the soil occasionally until germination begins in two weeks. Then, remove the plastic and continue growing the seedlings until you are ready to transplant them outside.
Potting and Repotting Globe Thistle
Container growing allows you to control globe thistle’s rampant tendencies. Plant it alongside other drought-resistant plants, such as yarrow or lavender cotton, to combine contrasting colors and textures. The long taproot of globe thistle presents some potting challenges. For this reason, choose a large terracotta or clay pot with ample drainage for your plant’s permanent home. Use a sandy loam or cactus potting soil and only repot your thistle when the plant is outgrowing its container and needs to be divided.
Overwintering
Once globe thistle has stopped blooming (either in the ground or in a pot), cut the plant back to the basal foliage, and then simply leave it be until next season; it does not need any winter protection. Cease watering during the winter, throughout the dormant season, and only begin watering again once new growth appears in the spring. If you want your potted globe thistle to survive until the next season, make sure your plant’s variety is at least two zones hardier than your climate so it can withstand a deep freeze. Leave it outdoors during the winter but wrap the container in burlap and bubble wrap to protect the roots, or build an insulating silo.
Common Pests & Plant Diseases
Pests rarely move into a healthy crop of globe thistle, yet neglected plants and wet growing conditions make the perfect habitat for aphids and the four-lined plant bug. Neither infestation will kill the plant, but you will notice the appearance of bugs and cosmetic degradation. Usually, a few blasts from the garden hose is enough to reduce the population. Perform this several times for best results. Once the weather warms and the soil dries out, the situation should remedy itself. This cousin of a prolific weed rarely experiences plant disease, yet crown rot, a lethal fungus, can move in during humid conditions. This fungus resides in wet soil and can only be remedied by drying out the ground. Prevent this condition by allowing your globe thistle to dry out in between waterings.
How to Get Globe Thistle to Bloom
Globe thistle does not require extra care in order to bloom. When the correct conditions of full sun and well-drained soil are provided, this plant should bloom from late spring throughout the summer. Cut spent blooms during the height of the growing season to encourage rebloom and to extend the flowering season.
Common Problems With Globe Thistle
The most common problem with globe thistle is incompatible soil (heavy clay or poorly drained), which leaves the plant susceptible to root rot and fungus. Prevent overwatering to avoid this situation. This plant does not fare well in overly rich soil, as well, and will fail to thrive or bloom in these conditions.
