Marsh daisy

Year-round

Year-round care for sea thrift around Seattle, WA: full sun and dry, well-drained soil.

• It grows best in full sun in lean, dry, well-drained soil.
• Good drainage is essential, because the leafy mounds tend to rot in the center in moist, rich soil or heavy clay.
• Calscape lists fast drainage and no more than two summer waterings a month once established.
• Plants stay 6 to 12 inches tall and about as wide.
• Deadhead spent flower stems to encourage more bloom.
• It is listed for zones 4 to 8.

Its low, grass-like mounds make a neat edge at the front of a bed.

Year-round

Sea thrift is not native to Iowa. The Lady Bird Johnson Wildflower Center lists its native range as the Pacific coast, Alaska, Colorado, and circumpolar tundra, not the Midwest, so this is a garden perennial here, not a native planting. It can still do well in a Des Moines bed if the soil drains sharply, since heavy clay and wet weather, not cold, are what actually kill it in this climate.

• Choose the driest, sunniest spot in the bed. Full sun is required for good growth.
• Work coarse grit, sand, or perlite into clay soil before planting, or use a raised or mounded bed instead.
• Keep the soil lean. Skip fertilizer and rich compost, both encourage the crown rot that kills this plant in the Midwest.
• Give plants room to breathe. Crowding raises humidity around the crown and invites rot.

Fall

Do not cut sea thrift back to the ground this fall the way you might with many other perennials. University of Wisconsin Extension notes that cutting the evergreen foliage back in fall reduces next spring's bloom. Fall is also the riskiest stretch of the year for this plant in Iowa, since a wet, cool fall followed by clay that will not drain is a leading cause of the crown rot that kills it here.

• Leave the evergreen foliage tufts in place. Remove only leaf blades that are fully brown or dead.
• Recheck drainage before the ground freezes. A wet fall in clay soil is the top risk to this plant over winter.
• Skip fall fertilizing.
• A light trim of just the dead flower stems keeps the clump looking tended without cutting the plant back.

Leaving the evergreen foliage up through fall, instead of cutting the whole plant to the ground, reads as intentional bed structure rather than neglect, and a light trim of just the dead flower stems keeps the edge looking tended.

Winter

Sea thrift keeps its low, grassy evergreen mounds through an Iowa winter. University of Wisconsin Extension lists it hardy to zone 4a, well past what Des Moines winters require, so cold is not the risk here. What actually threatens it is a soggy crown sitting under melting snow or ice in a low spot, which is why the fall drainage check matters more than any winter covering.

• No winter mulch or wrapping is needed. This plant is hardy well beyond typical Des Moines winters.
• Do not pile shoveled snow onto the clump. Extra meltwater at the crown is the real winter hazard.
• The low evergreen tufts stay visibly green through winter rather than dying back to bare dirt.
• Skip winter watering. A dormant plant wants dry conditions, not wet ones.

Spring

Sea thrift blooms in mid to late spring here, pushing up round pink, white, or lavender flower heads on bare stems above its grassy evergreen tufts, per University of Wisconsin Extension. Spring is also when Iowa clay tends to hold the most water from snowmelt and rain, so this is the season to check that the crown is not sitting in standing water.

• Expect bloom sometime in April or May, depending on the spring.
• Check the bed right after snowmelt for standing water at the base of the plant.
• Do not fertilize at spring green up. This plant wants lean soil, not rich soil.
• Deadhead spent flower stems back to the foliage to encourage more blooms later in the season.

Summer

Keep deadheading through summer since sea thrift reblooms sporadically on new stems, per University of Wisconsin Extension. Once established it is drought tolerant, so water only during a real dry stretch, and water at the soil line rather than overhead, since humid air plus wet foliage is what invites rust spotting and crown rot in an Iowa summer.

• Deadhead spent stems through the season to keep new blooms coming.
• Water only during extended dry spells. Established plants prefer dry conditions.
• Water at the base, not with an overhead sprinkler.
• Skip heavy mulch against the crown. It traps moisture in humid weather.