Sunflowers (Cover Crop) - Key Growing Information
Uses: As a cover crop, sunflowers produce lots of biomass, break up compacted soil, scavenge nutrients and feed beneficial insects with pollen and nectar. They also work for edible seed and birdseed.
Culture: Sunflowers are a warm-season crop, so hold off sowing until the soil is at least 60°F (16°C), with 70–85°F (21–29°C) being ideal. Plant 1–1½" deep with a seed drill or garden seeder, or broadcast and harrow in lightly.
Seeding Rate: ½–1 lb. per 1,000 sq. ft.; 15–40 lb. per acre.
Light/Soil Requirements: Sunflowers like full sun and well-drained soil with a pH of 5.5–7.8.
Height: 7'
Harvest: For birdseed or eating, cut the heads once the petals have dropped and the seeds are mature. Thresh by rubbing the heads across ½" hardware cloth stretched on a frame over a box, then spread the seed to dry.
Termination: Mowing at flowering or a hard frost will kill sunflowers. Left standing after winter-kill, they feed birds over winter and their stems give pollinators places to nest. Residue can be hard to manage, though, and may need aggressive tillage to bury stalks and root balls, so chop winter-killed plants as finely as you can before working them in. They're a poor choice ahead of crops that need a fine seedbed, and plants allowed to set seed can come back as volunteers next season.
