Product Field NotesCompanion Plants
Cape Cod Boys Siberian Iris: Periwinkle Blooms for the Moist Border
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Cape Cod Boys Siberian iris brings a seaside feel to early summer: periwinkle blue flowers with darker blue veins that build into a pattern toward the petal tips, each lit by a clear lemon-yellow signal. It earned the Morgan-Wood Medal in 2021, the top honor given to Siberian irises, after an Award of Merit in 2016.
It is a close neighbor to lavender rather than a bedmate. Siberian iris wants steadier moisture than lavender will tolerate, so it shines in the damper border next door.
Cape Cod Boys at a glance
| Trait | What to expect |
|---|---|
| Botanical name | Iris sibirica 'Cape Cod Boys' |
| Flowers | Periwinkle blue with darker veins and a lemon-yellow signal; slight sweet scent |
| Foliage | Wider than most Siberian irises, grassy and blue-green |
| Size | 27 to 32 inches tall, 18 to 24 inches wide |
| Bloom | Early to mid-June over a long stretch |
| Hardiness | USDA zones 3 to 9 |
| Light | Full sun to part shade |
| Wildlife | Good for pollinators; deer resistant |
Where it fits in a lavender garden
Picture a sunny lavender bed on higher ground and, a few steps away, a lower strip that stays damp after rain. That second spot is where Cape Cod Boys belongs. Its flowers open in early June, just before most lavenders begin, so the blue season starts with the iris and carries on with the lavender.
The pairing works visually too. Periwinkle and lavender purple sit side by side on the color wheel, and the iris's upright, sword-like leaves give the garden a strong vertical line after the flowers are gone. Its foliage is wider and bluer than usual for a Siberian iris, so the clump still looks good in August. Map out the two zones in the Companion Plant Planner.
Planting and care
- Planting: set the bare root plant with the crown just below the soil surface and water it in well.
- Water: keep the soil evenly moist, especially in spring and early summer. Water deeply in hot, dry spells to keep the leaves fresh after bloom.
- Soil: average to rich. Unlike lavender, it welcomes some compost.
- Problems: rarely troubled. Waterlogged soil can cause crown rot, and it sees much less iris borer damage than bearded irises.
- Black walnut: not bothered by it, which makes it useful under or near walnut trees.
- Winter: very hardy. Cut the foliage back in late fall or early spring; no winter mulch needed.
Divide crowded clumps in late summer when the center begins to thin.
For the vase
Cape Cod Boys is a good cut flower. Cut stems when the first bud is just opening and more buds are waiting behind it. A few periwinkle irises with fresh-cut lavender in a jar make an easy early-summer bouquet. Iris leaves and rhizomes are not edible and can upset the stomach.
Frequently asked questions
Can I plant it right in the lavender bed?
It is better nearby. The steady water the iris wants would keep lavender roots too wet. Give each its own zone.
Does Cape Cod Boys rebloom?
Count on one long bloom in early to mid-June. Some gardens have reported a little rebloom, but think of it as a bonus.
How is it sold?
As a bare root plant, ready to set into the garden. See the product page for current availability.
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