Cobalt Frost Dahlia Bulbs

Two colors, hard edge. Most blue dahlias blend from blue to white across the petal; this one blocks them — cobalt on one half, white on the other, with the boundary visible on every petal. The effect from across a garden is a flower that vibrates slightly, and up close it looks painted.

What you get

• Graded tubers with a visible eye, packed in peat.
• Blooms 5–6 in, fully double, with a dark center.
• Plants 32–40 in tall — stake in exposed sites.

An honest note

High-contrast bicolors photograph better than they garden. In flat light the white sections dominate and the flower looks washed out; in sun the cobalt reads as intended. Grow it somewhere it gets direct light for most of the day.

How to plant

• Soil temperature matters more than the calendar. Wait until it holds 60°F / 15°C at 4 in deep — normally about two weeks after your last frost.
• Lay the tuber flat, eye up, 4–6 in under the surface, and leave 15–18 in between plants for airflow.
• No water until shoots appear. A dormant tuber in wet soil rots in about ten days; roots don’t form until the shoot breaks through.
• Six hours of sun minimum, and a stake in at planting time if the variety runs tall. Driving one in later spears the tuber.

Hardiness & season

• Perennial in USDA zones 8–11, grown as an annual or lifted and stored over winter in zones 3–7.
• First flowers 8–10 weeks after planting, then continuous bloom until the first hard freeze.
• Pinch out the growing tip at 12 in for a bushier plant with more, smaller stems — skip it if you want a few large blooms.
• Keep cutting and deadheading. A dahlia allowed to set seed stops producing buds, and the September flush never happens.