Global: Chitting Seed Potatoes Speeds Emergence by 8–10 Days, but Warm Storage Can Cut Yield
An AHDB review shows chitting cut time to emergence by 8–10 days and can bring maturity up to two weeks earlier. A 2024 study found storage at 17°C cut yield of one variety by up to 30%.
Seed potatoes age before they are planted. This physiological age changes how fast the crop emerges, how many stems it forms and when it matures. A 2021 research review for AHDB by Carvalho and colleagues explains how growers can measure and manage it.
Counting day-degrees
The review measures physiological age as accumulated day-degrees: the sum of daily mean store temperatures above 4°C. For example, 25 days at 14°C give 250 day-degrees (our calculation). Seed kept at 4°C gains almost no age, while warm storage ages it quickly.
For chitting, the review describes seed held at 10°C for 4 to 6 weeks before the planned planting date. In one method, store temperature is raised by 1 to 2°C a day to 18–20°C until sprouts appear, then lowered to 8–12°C with light. Suggested lighting is more than 100 W per tonne, or LED lighting at 10 W per square metre, for 8 to 10 hours a day, with humidity at 70–80%. Sprouts should be about 1–2 mm long when light exposure starts.
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Faster emergence, earlier maturity
In a UK trial cited in the review, chitting cut the time to 50% emergence by 8 to 10 days in the varieties Markies and Pentland Dell. Chitted seed can mature up to two weeks earlier than unchitted seed. In Belgium, extending chitting to 7 weeks increased yields by 3 to 6 t/ha. The New Brunswick agriculture department in Canada also says green sprouting can advance maturity by about two weeks. It suggests warming seed at 10–15°C in the dark, and planting only when soil is at least 7°C.
Not a yield guarantee
Older seed does not always mean more yield. A 2024 study in Potato Research by Zou and colleagues stored seed of Agria, Festien, Innovator and Lady Claire at 4, 7, 10 and 17°C. The authors found no clear or consistent effect on final yield for storage between 4 and 10°C. Storage at 17°C more often reduced yield, with losses of up to 30% for Innovator at one site. Effects on stem and tuber numbers depended on the variety.
Why it matters
Seed age is a tool, not a fixed benefit. Early markets and short seasons gain most from chitting, because faster emergence and earlier bulking bring an earlier harvest. For long-season crops, too much warmth before planting can reduce yield in some varieties. Growers should record store temperatures, count day-degrees for each seed lot and test how their own varieties respond.
Photo: Chitting seed potatoes on a farm (illustrative). Richard Humphrey / Wikimedia Commons, CC BY-SA 2.0
