Attractive, Sea Holly plants (Eryngium) are striking ornamental perennials grown for their arresting, thistle-like, silvery or blue tinted flower heads adorned with a ruff of showy bracts. Blooming in summer and sometimes into fall, they are useful in rock gardens, coastal gardens and in borders where their steel blue flowers and foliage complement the vibrantly colored summer flowers. Their beautiful texture, unique color, long-lasting flowering and remarkable qualities as cut flowers make them a favorite of florists, gardeners, bees and butterflies. They are exceptionally care-free plants if they are given a well-chosen site. Here are some basic rules that need to be followed to enjoy their splendid flowers.
1. Select The Right Site
- Eryngium prefers full sun - at least 6 hours of direct sunlight per day.
- Eryngium prefers dry, poor to moderately fertile, well-drained soils with the exception of Eryngium pandanifolium (Giant Sea Holly) which prefers moist soils.
- Good drainage is critical or your plant will die off from root rot.
- Most Sea Holly species are reliably perennial in Hardiness Zones 4 - 9. Exceptionally hardy, Eryngium alpinum is perennial in Zone 2. Eryngium amethystinum and Eryngium yuccifolium are perennial in Zones 3. Not sure about your growing zone? Check here.
- Eryngium needs winter protection and a warm site in order to allow the rosettes to overwinter successfully, otherwise these plants use up all their energy replacing foliage.
- Eryngium is a taprooted plant that transplants poorly and is best left undisturbed once established. Select your site carefully!
2. Planting Your Eryngium
- Most Sea Holly varieties can be started from seed. Seeds should be sown in late summer and fall. They will germinate in the following spring.
- Sea holly transplants easily as seedlings, but it gets more difficult as the plants mature.
- Eryngium plants are relatively care-free once established.
- Sea Holly plants do not require much watering except during long periods of drought.
- Sea Holly plants do not require fertilization either. They may sprawl if grown in overly fertile soils.
- Deadheading will promote additional blooming.