Obsidian Fire Dahlia Bulbs

Black until the sun hits it, then bronze. The petals are dark enough to read as true black in shade, but each one carries a bronze sheen that catches on the rolled edges and turns the flower into something closer to a lit coal. It’s a cactus type — narrow petals, each rolled into a point — which is why the outline stays spiky instead of rounding off as it ages.

What you get

• Graded tubers, each with at least one visible eye, packed in peat to arrive plump.
• Blooms 5–6 in across with rolled, pointed petals rather than flat ones.
• Plants 36–44 in tall. Cactus dahlias run tall; stake this one at planting.

Where it works

Dark flowers disappear against dark fences and vanish in shade. Put this in front of something pale — limestone, a white wall, silver foliage — and the whole point of the color becomes visible.

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.