How to Grow and Care for Globe Thistle

Globe thistle is a fast-growing, contemporary-looking perennial plant with spherical blue, purple, or white blooms that add arresting color to summer border gardens. Yet unlike other eye-catching perennials, globe thistle is drought tolerant, deer resistant, and an important nectar source for pollinators like butterflies and bees.

Plant globe thistle in May or June to achieve mid-summertime blooms that last throughout the fall. After it blooms, globe thistle continues providing textural interest with attractive seed heads. The best growing conditions for globe thistle are at least six hours of direct sunlight, well-drained acidic soil, and ideal temperatures between 65 and 75 degrees Fahrenheit.

Globe Thistle Care

Here are the main conditions for growing globe thistle:

• Requires a full sun location.
• Prefers rocky, sandy, well-draining soil; clay can kill this plant.
• Tolerates drought conditions.
• Thrives in an acidic environment from pH 5.5 to 7.
• Handles a range of temperatures, but 65 to 75 degrees Fahrenheit is ideal.
• Does not need fertilizer or enriched soil.
  

Warning

Technically, globe thistle is noninvasive but is extremely prolific. This plant likes dry, nutrient-poor soil and can thrive in hot and dry environments. A closely related species, the Scottish thistle, is an invasive species to avoid. Globe thistle can still overgrow a space, overtaking other nearby plants, so deadhead this plant's flowers as soon as they wilt to prevent it from reseeding on its own.

Light

Globe thistle needs a full day of sun (at least six hours) 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. Globe thistle will fail when planted in heavy clay soil or kept in wet conditions; its taproot will become susceptible to root rot. If your landscape is 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 it to survive even the harshest 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. This plant is ideal for a xeriscaped environment.

Temperature and Humidity

Globe thistle plants thrive in warm, dry regions with ideal growing temperatures around 65 F to 75 F. However, 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. The best place to plant globe thistle is alongside drought-resistant plants, such as yarrow or lavender cotton, to combine contrasting colors and textures. White blooms work well combined with almost any annual or perennial. Here are a few gardener's favorites:

• Echinopssphaerocephalus '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': deep blue flowers blend nicely with its curved, silvery stems. This variety's blooms 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 garden areas.
• Echinops bannaticus'Taplow Blue': steely-blue flower heads with white tips resembling mini disco balls atop muted gray-green leafy stems. This variety grows 5-foot stalks, making it the perfect addition to the back of a perennial garden.

How and When to Prune Globe Thistle

Globe thistle is pruned for aesthetic purposes and to encourage rebloom. When pruning globe thistle, wear gloves since the spiny leaves and stems can hurt bare hands. Use sterilized pruners.

Occasionally, the flower heads become heavy, causing the plant to droop. Stake the plant or cut the flower in its prime for interior bouquets.

After the flower fades in summer, cut the flower stem down to its base to spur the plant to potentially develop more flowering stems. Bag the flower heads and cut the flower stem at its base to prevent reseeding when deadheading.

In late fall, before winter sets in, cut dead growth to ground level.

Propagating Globe Thistle

Globe thistle can be propagated by division for transplanting or gifting in another section of the garden. Wait until the plant is at least three years old when you can see new plantlets at its base.

Here's how to propagate globe thistle by division:

1. Gather gloves, a spade shovel, a sharp knife, and alcohol wipes.
2. Dig up the entire plant with a spade shovel in the spring, severing its taproot.
3. Lay the plant on its side in the garden, with roots exposed. Sterilize the knife with the alcohol wipes and allow it to dry.
4. Using the knife, cut a portion of the taproot lengthwise, separating the plant so that each side has a part of the taproot, lateral roots, and above-ground growth.
5. Dig a hole in your garden for the new division using the shovel. Plant the division at the same depth as the mother plant, backfilling the soil to cover the entire root system.
6. Replant the mother plant in the same fashion.
7. Water the division and the mother thoroughly.

How to Grow Globe Thistle From Seed

Globe thistle can be propagated easily by seed. 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.

Here's how to propagate from seed outdoors:

1. Collect spent flowers in the fall by harvesting the seed head and removing the seeds.
2. Sow the seeds outdoors that fall by placing the seed on top of the soil. Lightly scatter soil on top, hardly covering the seed. Space seeds at least 18 inches apart.
3. After the first spring frost, water your bed until germination occurs.

Here's how to start seed indoors:

1. Seeds need to be stratified or tricked into thinking they have endured winter. The coming of spring spurs germination. Stratify seeds in a moist seed-starting mixture and refrigerate them for at least four weeks.
2. Sow seeds indoors for two months before the last frost by filling a seed tray with seed starting mix, dispersing the seeds on the soil, covering lightly, and misting the soil.
3. Cover the tray with plastic and locate it in a sunny window where you can maintain 70 degrees F temperatures. Mist the soil occasionally until germination begins in two weeks.
4. Once the seed sprouts, remove the plastic and continue growing the seedlings until you can transplant them outside.

Potting and Repotting Globe Thistle

Container growing allows you to control globe thistle's rampant tendencies. However, the long taproot of globe thistle presents some potting challenges. For this reason, choose a large terra-cotta or clay pot with ample drainage for your plant's permanent home.

Use sandy loam or cactus potting soil, and only repot your thistle when it is outgrowing its container and needs to be divided.

Overwintering

Once the globe thistle has stopped blooming (either in the ground or pot), cut the plant back to its base and leave it until the next season; it does not need winter protection. Cease watering during the winter and 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. To treat it, a few blasts from the garden hose will usually reduce the population. Perform this several times for best results. Once the weather warms and the soil dries out, the situation should remedy itself.

Refrain from using pesticides on this plant. Globe thistle's spiny, spiky foliage is essential in the garden as a host plant for the finicky painted lady butterfly.

Rabbits and deer also don't seem to care much for grazing on this plant.

This plant 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 the ground. Prevent this condition by allowing your globe thistle to dry out between waterings.

How to Get Globe Thistle to Bloom

Globe thistle does not require extra care to bloom. It should bloom when full sun and well-drained soil are provided.

Bloom Months

Globe thistle typically blooms from July to September. However, months may vary depending on climate conditions. If you have milder spring temperatures, it may even begin flowering in late spring.

How Long Does Globe Thistle Bloom?

Blooms typically last from midsummer to early fall. However, the plant can rebloom if you deadhead or cut flower stems to the base after flowering or if temperatures and climate favor a more extended bloom period.

What Do Globe Thistle Flowers Look and Smell Like?

Globe thistle flower heads look like spiky pom-pom balls on the end of tall stems. The globes are about 2 inches in diameter and comprised of tiny star-shaped flowers. Colors are usually blue, purple, or sometimes white. The flowers have no scent.

How to Encourage More Blooms

Cut spent blooms during the height of the growing season to encourage rebloom and extend the flowering season. You can also trim the basal leaves or cut the stems down to their base to promote another round of flowers.

Deadheading Globe Thistle Flowers

Deadhead spent flowers and use them in dried flower arrangements. Deadheading prevents reseeding, keeps the plant's growth in check, and encourages rebloom. To deadhead without spilling the seeds in the garden, place a small bag over the flower head and cut it off at the stem.

Common Problems With Globe Thistle

Globe thistle is a low-maintenance, drought-tolerant plant. The most common problem is incompatible soil (heavy clay or poorly drained), which leaves the plant susceptible to root rot and fungus. Do not overwater to prevent this situation from occurring. This plant also does not fare well in overly rich-soil and will fail to thrive or bloom in these conditions.

From: thespruce