Harvesting sunflowers

Harvesting is the calmest part of growing sunflowers: the plant does the work, and you mainly wait for the right moment and then get the seed properly dry. The two mistakes people make are harvesting too early — when the seed isn't filled out — and storing it too damp, so the whole head goes mouldy within a week. This guide walks through the whole harvest, from recognising a ripe head to the packet of seed you push back into the soil in May. To see how you got this far, read the growing guide on sowing and care.

When is a head ripe

The most reliable sign is on the back of the flower head, not the front. During flowering that back is fresh green. As the seed ripens it turns yellow and finally yellow-brown, and the bracts around the rim become papery and dry. The yellow ray florets — the "petals" — have long since dropped, and the head often droops under its own weight. Only then is the seed full.

Check the seed itself, too. Ripe seed is firm, filled out and shows the variety's typical black-and-white or grey stripes. Squeeze a few seeds from the centre of the head: if they are flat, empty or milky inside, wait longer. In temperate Europe this point falls for most varieties from late September, roughly 110 to 130 days after sowing. A cool, wet autumn pushes it back a week or two — the same effect of temperature that Wageningen University & Research describes for growth overall, and that also drives the sowing calendar.

How do you know whether to wait for seed or for the flower? It depends on your goal. If you want the seeds, let the head ripen on the plant as long as possible. If you mainly want a cut flower, harvest much earlier — see the individual varieties for that. The rest of this page is about harvesting seed.

Cutting the head

Once the back is yellow-brown, you can harvest. Cut the head with about 30 cm (12 in) of stem attached — that stem is handy for hanging the head up later. Do this on a dry day so you don't bring damp material indoors. A ripe head from a tall variety such as Russian Mammoth can be heavy, so support it as you cut.

Not sure the seed is fully ripe, but birds or a wet spell threaten to spoil the crop? Then harvest the head a little early and let it finish ripening and drying indoors. It costs a few extra weeks but saves the seed. Against birds pecking at the ripening head, it helps to tie a net or a paper (not plastic) bag loosely over it once pollination is done; plastic traps moisture and actually causes mould.

Drying the seed

Drying is the step where most harvests go wrong. Seed put away too damp goes mouldy — and mould on seed makes it worthless both for sowing and for eating. The rule is simple: plenty of air, little moisture, and patience. Hang the head upside down somewhere dry and well ventilated, out of rain and dew: a shed, loft, garage or covered porch. A temperature of 15–25 °C (59–77 °F) with dry air works best.

Stretch a net or cloth beneath the head, because seeds always fall out as it dries. Allow one to three weeks, depending on humidity. The head is dry enough when the seeds release easily and the whole head feels light and stiff. In a damp autumn, drying outdoors often fails; bring the head inside then. The same fungi that attack a wet crop — think of sclerotinia and powdery mildew — also strike a head that dries too slowly. Air is your best defence.

Releasing the seed

Once the head is dry, get the seeds out. Rub two heads together over a bucket, or brush your hand or a stiff brush across the disc. The seed then releases by the handful. What remains is chaff — bits of flower base and disc florets — which you sieve or blow away. A ripe, dry head gives up its seed with almost no effort; if you have to pull and pick, the head wasn't dry enough and goes back to dry further.

Storing the seed

Store well-dried seed airtight, dark and cool. A glass jar with a lid, a tin or a well-sealed bag all work; add a sachet of silica gel or a spoon of dry rice to catch residual moisture. Write the variety and harvest year on the label — a year from now you won't remember otherwise. Kept somewhere cool and dry, sunflower seed stays viable for at least one to three years, though germination falls off over time.

To store seed for longer or for eating, the fridge or freezer works. Only freeze fully dry seed; moisture expands and damages the kernel. Check a stored jar now and then: if it smells musty or you see a film, moisture has crept in and the seed is best thrown away.

Seed for next year

Saving your own seed is one of the most rewarding parts of growing — but it doesn't work with every variety. The difference lies in the parentage. An open-pollinated variety produces offspring that resemble the mother plant; you can keep sowing from it for years. An F1 hybrid is a cross of two parent lines, and the second generation breaks up into all sorts of forms that rarely look like the plant you bought. Seed from, say, ProCut Orange, an F1 hybrid, therefore gives no reliable copy.

To be sure whether you can save from a variety, check the seed packet or our cultivar database for whether it is open-pollinated or an F1. When saving seed, also bear in mind that sunflowers cross-pollinate: if several varieties stand close together, the offspring can mix. To keep a variety pure, grow only one that year, or isolate the plants. How pollination works and who does it is explained under the anatomy of the head.

Roasting seed to eat

Seed from large-seeded varieties is perfectly edible. Rinse it clean, optionally soak it overnight in lightly salted water, and pat it dry. Then roast it in a dry pan or on a baking tray in the oven at about 150 °C (300 °F) until light brown and crisp — usually fifteen to twenty minutes, stirring regularly. To eat it in the shell, choose a striped variety with a thin hull; for kernels without shell, hulling is needed.

Note: seed you roast to eat, or that sells in shops as a snack, will not germinate afterwards. If you want both to eat and to sow, keep two batches apart — untreated seed for the soil, roasted seed for the pan. More on oil, nutrition and cooking is on the oil & food page.

Seed for the birds

Not everything has to go into the jar or the pan. A ripe sunflower head is a winter feast for tits, finches and sparrows. You can hang up a whole dry head or lay it on a bird table; the birds pick the seed out themselves. Leave a few heads on the plant deliberately as natural bird food. That way the sunflower you sowed in May ends the year doing what matters most for nature — feeding it. Which pollinators the flower feeds in summer is covered under bees & biodiversity.

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