A spiky, drought resistant perennial, sea holly (Eryngium maritimum) will thrive in a dry rock garden or near the ocean in sandy, saline soil. The spiky purple flowers bloom from July to October and attract bees, beetles and other pollinators. Sea holly grows as a perennial in USDA plant hardiness zones 5 to 11. In colder areas, it will grow as a summer annual and die back in the winter. Plant sea holly in full sun--this desert loving plant will suffer in a shaded spot.
Sow seeds in late fall for spring planting. Fill a seed-starter flat with damp, loose, well-rotted compost. Sprinkle the seeds on top of the damp compost.
Place the tray in a greenhouse or covered porch where the temperature is above 70 degrees F. The sea holly seeds will take five to 90 days to germinate.
Move the seedlings into deep 6-inch planting pots filled with rich compost when they are 2 inches tall. Handle the sea holly seedlings carefully to avoid damaging the long taproot.
Transplant the sea holly seedlings outside in late spring when all chance of frost has passed. Dig a hole that is slightly larger than the planting pot the seedling is in. Turn the potted seedling onto its side and gently wiggle it free from the pot.
Put the root ball into the planting hole. The base of the stem should be level with the surrounding soil. Fill in the soil around the root ball and pat down the earth around it.
Water the newly transplanted seedling until the soil is damp to a depth of 6 inches. After the initial watering, let the top 1 to 2 inches of soil dry out before watering again.
- Sea holly sends out a long, deep taproot. Transplanting a mature sea holly will damage the taproot, so pick the location carefully before planting. Small, young plants can be dug up and moved; dig deep and keep as much of the root ball together as possible.
- Sea holly can be invasive in warm climates. To stop it from spreading, clip off the flower heads before they go to seed.
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