Oca · Ōmuta, Fukuoka, Japan
When to plant oca in Ōmuta
Main outdoor window
10 Mar - 7 Apr
The window this page is built around.
Timed from last spring frost
10 March
In Ōmuta, on your chosen risk.
Ready to pick
1 Nov - 31 Dec
If you plant at the start of the window.
The average last frost. Half of all years are later than this.
Step by step in Ōmuta
Each window is a range, not a single day. Earlier in the range buys you a longer season; later in it buys you a safer one.
Plant tubers
10 Mar - 7 Apr
Around your last frost.
Harvest
1 Nov - 31 Dec
Oca through the year
Against the frost risk in Ōmuta
Why these dates
Plant tubers after the last frost. Do not lift until several weeks after the tops are frosted - almost all the crop forms in that final window, and digging early gets nothing.
Foliage is killed around -2C, but tuber formation happens in the weeks just before and after that. In short-season climates a fleece over the plants buys the time the crop needs.
Seed packets and extension guides express timing as weeks either side of the last spring frost, because that is the only reference point that travels. Oca are timed with planting out 0 weeks after it, and this page simply resolves those offsets against the frost date computed for Ōmuta.
Hardiness is not the obstacle here. Ōmuta is zone 9b, comfortably inside the range this crop is rated for, so an established plant should come through an average winter without protection.
The median frost-free season here is 279 days, against 180 to 210 days to maturity for this crop counted from sowing. That margin is what decides whether a late sowing is worth attempting.
Also in Ōmuta
Other vegetables to time
Growing oca in Ōmuta
When should I plant oca in Ōmuta?
Aim for 10 Mar - 7 Apr in an average year. If you would rather not gamble on the weather, wait until 27 Mar - 24 Apr - by then frost has finished in nine years out of ten.
When will oca be ready to harvest in Ōmuta?
Expect to start picking around 1 Nov - 31 Dec, based on 180 to 210 days to maturity from the planting date calculated for this location.
How much frost will oca tolerate?
Foliage is killed around -2C, but tuber formation happens in the weeks just before and after that. In short-season climates a fleece over the plants buys the time the crop needs.