When to Harvest Sunflower: Timing, Moisture, Losses

When: by the signs, not the calendar#

In Ukraine sunflower is harvested mostly in September and October, but the exact date depends on hybrid, zone and season, so the crop itself is the guide. The signs of readiness are these: heads have turned brown, their backs have darkened, the bracts have dried, ray florets have dropped, and seed separates easily under light pressure. Seed moisture at that point is 12–15 %. That is the threshing window. Assess average plants at several points across the field rather than the ones at the edge, because margins and low ground always lag. One reliable check is to break open a head in several places and look at the hull colour and the density of the kernel. If the outer seeds are dark and hard while those at the centre are still pale, the field has not entered the window: the centre of the head ripens last and it is what decides readiness.

The maturity stages, and why the window is narrow#

Understanding the stages explains the narrow window. After flowering, which lasts around two weeks, comes milk maturity: the seed is soft and fluid-filled, the kernel still forming. Then wax maturity — the seed hardens, moisture falls to roughly 20–30 %, and the head goes from yellow to yellow-brown. Finally full maturity at 12–15 % moisture. Mass accumulation is already complete by wax maturity, so waiting beyond it adds nothing to yield — it only dries the seed on the plant. That matters for the desiccation decision: treating before fill has finished locks in a shortfall which no saving on drying will recover. The planning conclusion follows: it is wax maturity, not full maturity, that fixes the size of the crop — by then you already know what you have, and everything after it is a question of keeping it.

What delay costs#

A late harvest is not neutral waiting — losses accumulate through several channels at once. Over-dried heads begin to shatter, and seed is knocked out by the mechanics of the header alone. Birds work open heads systematically rather than occasionally. In wet weather, white and grey moulds develop in over-ripe heads and damage both yield and oil quality. Plants lodged by rain and wind are picked up far less well. Together these add up: across an unfavourable week, losses run to several per cent of the crop. So once a field has entered the threshing window, harvesting starts — you do not hold out for a perfect forecast.

Drying and storage#

Sunflower stores less well than cereals, and the reason is its oil content: the fat oxidises, and damp seed raises its acid value quickly, which directly reduces the price. For long-term storage dry the seed to 8 % or below; for short-term, to 9 %. Dry it gently — overheating damages the kernel and spoils oil quality, so drying air temperature for sunflower is always lower than for wheat. After drying, cool the batch before storing it, or the warm mass will condense moisture. Monitoring is the same as for grain: temperature at several depths, moisture by meter, and a check for self-heating every fortnight. What differs from grain is that sunflower's low bulk density and light hull make the mass prone to uneven airflow, so aeration should be verified at several points rather than trusted to a single sensor.

The header matters more than the combine#

Sunflower needs a dedicated header with pans matched to the row spacing, not a grain header: a grain header cuts stems along with the heads, sharply raises the moisture of the harvested mass and blocks the threshing drum. Check the header's row spacing against your own before going to the field — a mismatch knocks heads off and costs you seed on the first pass. Set drum speed to the minimum that threshes cleanly: sunflower threshes easily, and excess speed cracks kernels and produces fines that lower the grade. Match forward speed to crop density: an overloaded drum leaves seed behind, while crawling increases shattering. Treat the first hectare as a check and stop to count losses behind the header.