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Sea Holly

Eryngium

Most people don’t have many good things to say about thistles. However, sea holly may change that opinion with stunning steely-blue thistlelike flower heads that last a long time and add texture to the garden. They are extremely tough plants that can thrive even if neglected. Sea holly can grow in some truly tricky situations, such as gravel.

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Light:

Sun

Type:

Height:

From 1 to 8 feet

Width:

1 to 3 feet wide

Flower Color:

Foliage Color:

Seasonal Features:

Problem Solvers:

Zones:

4-10

Propagation

Sea Holly Colors

Sea holly plants make a dramatic companion to plants in the garden with their spiny foliage and flowers. In addition to their texture, the foliage and blossoms come in a metallic blue that is one of a kind. Since the blue flowering bracts aren't actually a blossom, the bracts hold on to their color longer—offering an extended show of color. Leaves of the sea holly are also attractive, often with white or silver streaks and veins or an overall cast of silver.

Need more reasons to love your pernnials? Find out how they can solve your landscaping problems.

How to Grow Sea Holly

Native to grasslands and rocky plains and coasts, these plants thrive in adversity, whether it is neglect or harsh conditions. They favor dry, poor soil. Their one weakness: too much water. You can easily kill sea holly in soil that stays too wet. Rich soil with lots of organic matter encourages lush, soft growth and causes sea holly to grow and then flop oven.

Make sure to give sea holly full sun. In part sun, the plants will most likely flop and have less than ideal coloring. They will also bloom more sparsely and lose some of their spiky appeal. In order to really thrive, they need heat too, so less than full sun won't give them all the warmth they require. 

Although they aren't a true thistle, these tough plants do share a lot of similarities to the common garden weed. Some varieties can be somewhat weedy—you may find plenty of volunteer seedlings around the garden. Sea holly, when perennial, tend to be fairly short-lived. It is best to leave a few seedlings just in case it is their last year. If they aren't right where you want them, you can dig them up and transplant them to a new spot, but this is best done when plants are young; most sea holly have a large taproot, making them tricky to transplant. This also means plants that are several years old are generally hard to move .

See more plants that thrive in clay.

New Types of Sea Holly

Many of the newer types of sea holly boast dwarf habits, which is beneficial as some can become quite large. There are also varieties that feature richer blues and even a few with golden foliage that creates a stunning look with the steel blue flowers.

More Varieties of Sea Holly

Alpine sea holly

Eryngium alpinum has deeply serrated bracts (petals) surrounding a central cone, giving the flower a lacy appearance. It grows 3 feet tall. Zones 5-8

Amethyst sea holly

Eryngium amethystinum is the hardiest species. It bears purple-blue flowers on plants 2-1/2 feet tall. Zones 2-10

Flat sea holly

Eryngium planum has silver-blue flowers on plants 2-3 feet tall. Its leaves are scalloped rather than spiny. Zones 5-10

'Miss Willmott's Ghost' sea holly

Eryngium giganteum gets its name from its dramatic ghostly gray-green to silvery blue flowers on plants up to 6 feet tall. Also sometimes called giant sea holly. Zones 5-10

'Rattlesnake Master' sea holly

This variety of Eryngium yuccifolium is a native of the Great Plains. It is a stately plant that reaches 4-5 feet tall and bears silvery white balls on spiny foliage that resembles that of yucca. Extracts of the plant were used by Native Americans as medicine. Zones 4-8

'Sapphire Blue' sea holly

This Eryngium selection, also sometimes sold as 'Jos Eijking', is a sterile variety that does not self-sow. Zones 5-9

Plant Sea Holly With:

Artemisia

Grow artemisias for the magnificent silver foliage that complements nearly all other perennials and ties together diverse colors within the garden. They're nothing short of stunning next to white or blue flowers.They thrive in hot, dry, sunny conditions such as a south-facing slope. A number spread rapidly to the point of being aggressive, so consider limiting yourself to varieties listed below that are well-behaved.

Daylily

Daylilies are some of the easiest perennials to grow, filling almost any space in the garden with a variety of shapes, colors, and sizes. Countless new hybrids are released every year in addition to the tens of thousands of cultivars already registered. Since the flowers last only one day for most plants (hence the name), you may want to grow lots of different varieties for a long-term display of color. Or look for reblooming varieties; some bloom continuously for months and others bloom a second time in the fall.

Yarrow

Yarrow is one of those plants that give a wildflower look to any garden. In fact, it is indeed a native plant and, predictably, it's easy to care for. In some gardens, it will thrive with almost no care, making it a good candidate for naturalistic plantings in open areas and along the edges of wooded or other wild places.Its colorful, flat-top blooms rise above clusters of ferny foliage. The tough plants resist drought, are rarely eaten by deer and rabbits, and spread moderately quickly, making yarrow a good choice for massing in borders or as a groundcover. If deadheaded after its first flush of blooms fade, yarrow will rebloom. If left to dry on the plant, flower clusters of some types provide winter interest. Flowers of yarrow are excellent either in fresh or dried arrangements.

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