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How to Grow Sea Holly

Are you looking for a fascinating addition to your garden? Then consider growing sea holly flowers, also known as Eryngium. Sea holly plants are extremely low maintenance, but they still require some care.

If you’re unfamiliar with sea holly plants and their growing conditions, it can be difficult to figure out how to care for your plant properly. This guide will help you through the process of growing and caring for a sea holly plant so that it stays healthy year after year.

What is Sea Holly?

Sea holly eryngium, also known as sea holly flowers, are European native plants that grow in a blooming spike. These flowers come in blue flowers or green cones and a distinctive bract collar in silver, white, green and bluish- purple. Their green or silvery blue stems grow to about six inches in height, topped with thistle-like flowers. Their common name comes from the thorny leaves that cover their stems and blooms.

Sea Holly Varieties

Several varieties of eryngium plants have been cultivated as garden plants are widely available in most nurseries. The most sea holly varieties include:

Rattlesnake Master

Also known as Eryngium yuccifolium, it produces light purple flowers with an oblong center with a blue eye in the middle. This flower is easy to grow and blooms from May through October. It derives its name from the myth that they can cure rattlesnake bites or drive them away.

methyst Sea Holly

This variety is known as E. amethystinum and has white flowers with a purple center. It typically blooms in early spring through summer. This European native is one of the most cold-hardy of the genus. It has beautiful blue flowers and a straggling nature.

Giant Sea Holly

Giant sea holly grows to heights up to eight feet tall and produces white flowers tinged with purple at the base. They are widely used as a filler in flower arrangements or bouquets because of their large number of thin spiny stems.

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Flat Sea Holly

These are one of the few Eryngiums to open, much like a daisy. They are very popular for cut flower arrangements because they can last nearly a week in water with good care. It produces numerous silver-blue flower heads.

The Jade Frost 

Japonica is known for its bright green color with purplish undersides on the leaves. This variety tends to grow upwards quickly and can potentially reach up to five feet tall. It boasts variegated foliage with pink margins and veins.

The Jade Frost 
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How to Grow Eryngium Plants

Growing sea holly plants is easy. All these perennial flowers will thrive in full sun and moist soil with good drainage. They prefer sandy soils and not any other moist soil. The long taproot of this plant makes it tolerant to poor soil conditions, plus, it’s drought tolerant.

Because of their long taproot, make sure you locate them somewhere permanent because they won’t transplant easily. You can sow seeds directly to the garden, although they may not bloom in the first year.

Caring for Sea Holly Flowers

Sea hollies are easy to care for. Once established, they don’t need much water or fertilizer to survive. Proper soil and sandy soils with full sun are what this plant requires to thrive.

Caring for Sea Holly Flowers
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Tall sea holly varieties need some support, so plant them in a place where they will have something to lean on. Sea holly will also bloom longer if you deadhead the spent flowers, but they’ll look wonderful long into winter. So you can leave the fall flowers on the stem. Sea holly flowers are popular with bees and butterflies but resistant to deer and rabbits.


Full sun to partial shade is what these plants require. At least eight hours of full sun a day will have them growing to their full potential. While sea holly plants can handle partial shade, light reduction may lead to weaker stems necessary to stake the plants to keep them upright.

Temperature and Humidity

As long as you plant your sea holly in proper hardiness zones, it doesn’t need additional temperature or humidity. While your flowers should be kept out of freezing temperatures, sea holly can survive hot and cold weather.


The best soil to plant sea holly is dry, sandy soil. It’s not a heavy feeder and doesn’t require fertilizer, but it will be in soils with high organic matter. Although it will still grow in poor soil, it’s good to amend your mixture with a little compost and peat moss before planting.

You don’t need to test soil pH for this plant as they’re not particular about it. Anything around the neutral range is just fine. However, it needs good drainage, or it will be susceptible to root rot and die off.


Sea holly flowers are not heavy feeders, but you need to ensure your soil has a decent amount of organic compost for healthy growth. You can make a composter if you want to have a good supply of some organic manure. If your soil is amended with compost or manure, this should be adequate to give sea holly plants enough nutrients during the growing season.


Watering is important to growing sea holly plants. Never let the soil dry out completely, even during dormancy over winter. During this phase, the plant becomes dormant and will shed its leaves, but it is still alive. Once spring arrives, new leaves will grow quickly on your sea holly plant.

Propagating Sea Holly

The taproot of this plant can make it a bit difficult to propagate. To do so using root cuttings, wait until the late summer, then cut the nice fat sections of roots. Do not cut away more than one-third of the plant’s total root mass.

Then, replant the parent clump immediately. Do not let the cuttings dry out. By fall, new roots will have formed, and you can transplant them into their small pots. To promote plentiful blooming, you need to deadhead your sea holly blooms as they begin to fade.

When your plants are near the end of the blooming season, usually around mid to late fall, avoid deadheading. The root segments should begin to generate new roots in the spring. When you see green roots emerging above the soil line, transplant your new sea holly plant into the garden.

Common Pests and Diseases of Sea Holly

Sea hollies are not prone to many pests or diseases. Root rot, slug, and powdery mildew are the only common diseases you might encounter. Root rot occurs when soil is waterlogged, so use all-purpose compost mixed with sand to promote proper drainage.

Powdery mildew can only become an issue with your plant if you don’t keep it dry or if you don’t expose it to full sun. However, you can remedy powdery mildew by treating your plants with baking soda spray or milk spray.

A slug can also bring menace to your plant, but if your plant is situated in a dry and sunny environment, then a slug will not be a problem. You can keep your plant from being damaged by slugs by using both beer and sand traps.

FAQs on How to Grow Sea Holly

How long does Eryngium take to bloom?

 Sea holly Eryngium takes a little while to grow, about a year or two. Once the sea holly Eryngium blooms, it can last up to ten years.

Is Eryngium poisonous?

This plant is not poisonous if consumed in small doses. However, you should keep this plant away from your pets and children because large amounts of Eryngium can be poisonous.

What is the benefit of growing Eryngium?

Eryngium is a beautiful wildflower, and it also has medicinal purposes. This plant can be smoked or brewed into a tea and cure some diseases and ailments such as asthma and bronchitis.

Final Thought on How to Grow Sea Holly

As you can see, growing and caring for sea holly isn’t too hard.  With a little research and patience, you can grow sea hollies and watch them transform your yard into a beautiful scene of blue and green.


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