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Giant sunflower

Helianthus giganteus

Helianthus giganteus

Regular price $6.48 USD
Regular price Sale price $6.48 USD
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Size

Sun/shade: Full sun to part shade

Soil moisture: Medium to wet

Height: 8'

Spread: 2'

Flowering period: September

Standing in a patch of giant sunflowers feels a bit like standing in a forest rather than a meadow. Growing up to 10 feet tall, these majestic beauties bring summer to a shining conclusion, with big yellow flowerheads that last through the month of September. Sunflowers evolved exclusively in North America and are among the most important plants for native bees. Found in NE Ohio meadows, wet meadows, and the margins of water bodies, giant sunflower grows best in moderately wet to average soils and full sunlight.

When gardening with giant sunflower, it is best to place the plant in a large garden bed to accommodate its immense height and tendency to spread via rhizomes. It is also important to plant giant sunflower in the company of robust neighbors that will form colonies that will resist encroachment. Some examples include late boneset, short-toothed mountain mint, wrinkleleaf goldenrod, swamp milkweed, and ironweed. Giant sunflower can also be planted along with tall grasses, like big bluestem, switchgrass, and Indian grass. The grasses will both restrain giant sunflower’s spread and offer the plant physical support, keeping it from leaning. Another option to keep giant sunflower from leaning is to trim it to half its height in June. This will cause the mature plant to be several feet shorter with a more branching form.

In terms of wildlife value, the sunflower genus, Helianthus, supports more pollen specialist bees than any other genus of plants in the eastern US. Pollen specialists require the pollen from a select group of plants – in this case sunflowers – for feeding their larvae. Many of these bees fall into the long-horned bee genus, and can be recognized by extremely long antennae, especially on the males. One curious habit of long-horned bees is that at night, males will latch onto plant stems with their mouthparts and sleep hanging from the stems. The bees will often do this in groups of 10-20 individuals, forming bee roosts. In addition to attracting long-horned bees, giant sunflowers attract mining bees, bumble bees, and migrating monarch butterflies. The plants also produce seed that is relished by birds, and the old flowerheads thus transform into natural bird feeders.

Photos by Julie Slater.

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