When and How to Harvest Chinese Arrowhead Tubers

Waiting for the tops to die back

The tubers fill at the very end of the season, after the plant has stopped making new leaves. Through late summer the runners are still traveling and the swellings at their tips are small and watery; through autumn those swellings harden, color up and take on the tight skin that lets them keep in storage. Lifting early costs you most of the crop, because the difference between a marble and a walnut is entirely made in the last few weeks.

So the signal to harvest is above the water, and it is unmistakable: the arrow leaves yellow from the outside in, then brown, then fall over, and no new growth replaces them. Once the tops are fully dead and collapsed, the plant has finished moving anything into the tubers and there is no reason left to wait. Frost on the leaves does the tubers no harm at all, because they sit deep in mud that the frost cannot reach.

There is no advantage in leaving them in the mud through winter, either. Tubers left in a bed sprout in spring and grow, which sounds convenient but means the bed becomes a permanent unmanaged stand at whatever spacing chance provides. Lift the lot, then replant from the best tubers next spring.

Do not test by pulling a plant. The tubers are not attached under the crown, so a pulled plant tells you nothing except that you have torn through the runners you were about to harvest.

Draining and working the whole bed

The single thing to understand is where the crop is. Arrowhead does not swell tubers under the plant. Each runner travels out horizontally through the mud, often a foot or two (30 to 60 cm) from the crown, and sets a single tuber at its tip, usually four to eight inches (10 to 20 cm) down. That means the harvest is spread across the entire bed, including the corners and the space you thought was empty, and it means a spade pushed in beside the stem finds nothing but runner.

Harvesting is done with hands, not tools. You drain the bed to firm the mud a little, then work it over systematically, feeling rather than looking, because the water will cloud within seconds of your first movement.

1. Cut the dead tops off first Clear the collapsed leaves and stalks off the surface and take them away. Working through a mat of dead foliage means you will miss tubers and you will keep mistaking stalk bases for them.
2. Drain the bed most of the way Siphon or bail until an inch (2.5 cm) or so of water is left. Fully dry mud is heavy and sticky; a thin film of water keeps the mud loose enough to move your hands through and rinses tubers as you find them.
3. Work in strips, not around the plants Start at one wall and work across the bed in strips a hand's width apart, so you cover every part of the surface once. Ignore where the plants were. The crop is not there.
4. Sweep, do not dig Push your fingers in to about eight inches (20 cm) and sweep them sideways through the mud. Tubers announce themselves as hard rounded knobs against fingertips. A fork or trowel slices them in half and slices the runners you were following.
5. Follow every runner you find When your hand meets a firm white cord, run along it outward with a finger. It will end in a tuber, or in the wall of the bed. This is how you find the ones that are nowhere near where you expected.
6. Go over the bed a second time Refill an inch (2.5 cm) of water to loosen the mud again and repeat the whole sweep at a different angle. The second pass reliably turns up tubers the first one missed, especially against the walls and in the corners.

Sorting and storing what you lift

Rinse each tuber in a bucket of clean water as you go and look at it properly. Keep the beak on. That long curved sprout at the top breaks off easily and is worth protecting on anything you intend to replant, and on tubers for the kitchen it tells you which end is which. Sort into three piles: sound tubers for eating, the best-shaped and firmest for replanting next spring, and anything cut, soft or bruised into a separate pile to use within days.

Arrowhead tubers do not keep like potatoes. The skin is thin, it does not cure and harden, and a tuber left in dry air shrivels within a couple of weeks and will neither cook nor grow. Store them damp and cool: bed them in barely moist sand or in damp coir in a box, so the tubers do not touch each other, and keep the box somewhere cold but frost-free, around 34 to 41F (1 to 5C). Check monthly, take out anything that has gone soft, and re-dampen the sand if it dries.

Seed tubers for next spring are stored exactly the same way, and they are the same tubers. Choose medium, well-rounded, unblemished ones with the sprout intact, keep them in their own labeled box so they do not get cooked by mistake, and expect them to start pushing pale beaks toward the end of winter. That is normal, and it is the point at which you start watching the water temperature in the bed.

Leaving none behind, and what to record

Every tuber left in the mud grows. That is the whole reason this crop is contained rather than planted in open ground, and it applies to the bed you are standing over as much as to a pond. A tuber the size of a fingernail missed in a corner will be a full-sized plant by midsummer, in the wrong place and at the wrong spacing, competing with the ones you planted deliberately. Go over the bed twice, and if you are emptying the container completely, tip the mud out onto a hard surface and rake through it rather than spreading it on a border.

Never dispose of spent arrowhead mud into a pond, a ditch, a bog garden or a compost pile that drains onto wet ground. Dry it out completely on hard standing first, in full sun, and only then use it. Tubers survive a long time in damp soil and will find any water you give them.

Finish the season by writing three things down: the date the tops finally died back, the total weight or count you lifted, and roughly how far from each planting position the tubers were actually found. That last number is the most useful record you will keep, because it tells you precisely how wide to space next spring and exactly how far out from each plant to sweep when you are harvesting blind in the mud a year from now.