Gadenin日本語Get the appHow the year is shaped
This is a long-season crop with one harvest, and the shape of the year is easy to hold in your head. Spring is establishment, when a tuber turns into a plant and nothing much appears to happen for a fortnight. Summer is leaf building and runner travel, when the plant makes the machinery but not the crop. Autumn is filling, when the runners stop and pour everything into the swellings at their tips. Winter is storage, both for the tubers in their box and for you, planning the spacing.
The important consequence is that almost the entire crop is made in the last stage. Anything that shortens the season at the end, lifting early because you are curious or because the bed is in the way, costs far more than the same number of weeks lost at the start. Conversely, planting a fortnight late into properly warm water costs almost nothing.
Nothing here is tied to a calendar date, because the triggers are temperature and the state of the plant. Water above 59F (15C) starts the season. The first standing arrow leaf starts feeding. The last new leaf ends feeding. Fully dead tops start the harvest. Learn those four signals and the crop runs itself in any climate that gives you a warm summer.
Stage by stage through the season
The table below is the whole cycle in order. Each row is triggered by something you can see or measure rather than by a date, so it reads the same in either hemisphere. Work through it in sequence and do not skip the thinning row, which is the one most often left out and the one that costs the most.
| Stage | Trigger | What you do | What to watch |
|---|---|---|---|
| Late winter | Sprouts lengthening in the store | Check stored tubers, re-damp the sand, choose the seed tubers | Shriveled or soft tubers, broken sprouts |
| Early spring | Frosts easing | Build or refill the bed with plain mineral soil, flood it, let it settle a day | Soil still slumping, water not cleared |
| Mid spring | Water above 59F (15C) for a week | Plant tubers beak up, 2 in (5 cm) deep, 12 to 18 in (30 to 45 cm) apart, 2 in (5 cm) of water | Floating tubers, buried sprouts |
| Late spring | First shoots showing | Net against birds, mark gaps, keep the water shallow and warm | Cold snaps checking growth |
| Early summer | Shoots about 4 in (10 cm) tall | Thin to one strong crown per tuber, pull weeds while small | Multiple crowns crowding each other |
| Early summer | First true arrow leaf standing clear | Start feeding: tablets pushed 3 to 4 in (8 to 10 cm) into the mud | Green water, meaning feed placed too shallow |
| Midsummer | Full leaf cover | Raise the water to 4 to 6 in (10 to 15 cm), top up daily, feed every 3 to 4 weeks | Aphids, caterpillars, dropping level |
| Late summer | Runners reaching the walls | Push escaping runners back into the mud, check the rim each top-up | Runners bridging out of the bed |
| Early autumn | Last new leaf sent up | Stop feeding. Hold the level steady while the tubers fill | Soft late growth from feeding on too long |
| Mid autumn | Leaves yellowing and falling | Let the level drop to 2 to 3 in (5 to 8 cm). Clear dead foliage off the surface | Impatience: do not lift yet |
| Late autumn | Tops fully dead and collapsed | Drain the bed, sweep the whole area by hand twice, lift everything | Tubers missed in corners and against walls |
| Late autumn | Harvest sorted | Box eating and seed tubers separately in damp sand, cold but frost-free | Tubers drying out, skins broken |
| Winter | Bed empty | Dry the spent mud on hard standing before reusing it. Plan next year's spacing | Stray tubers escaping into wet ground |
The decisions that actually change the outcome
Three points in that sequence carry nearly all the weight, and everything else is maintenance. The first is spacing at planting, because the tubers form at the far ends of runners and a crowded bed physically has nowhere to put the crop. The second is thinning to one crown, because a tuber that raises four shoots divides the same resources four ways and yields four times as many tubers a quarter of the size. The third is patience at the end, because the crop is made after the plant stops looking productive.
Two more decisions are about keeping trouble away rather than growing anything. Never let the mud go dry, not even for a day, and never let a runner or a tuber leave the bed. Both are single events with consequences that last the rest of the season or the rest of your time in that garden.
Heat is the one factor you can only partly control. Arrowhead does very little below 68F (20C) at the water surface and fills best through a long run of warm weeks. In a cool climate that means the hottest, most reflective, most open position you have, a bed wide enough to be worth the space, and no interest at all in an early start.
If you can only remember four numbers, make them these: plant when the water is above 59F (15C), space at 12 to 18 in (30 to 45 cm), thin to one crown, and lift only after the tops are completely dead.
What to record so next year is easier
Arrowhead is grown blind. From the moment the water clouds at planting until the moment you drain the bed in autumn, you cannot see the crop at all, so your notes from last season are genuinely the best information you have. Keep them short enough that you will actually write them.
Record six things: the date and water temperature at planting, a sketch of where each tuber went, the date the first standing arrow leaf appeared, the dates of each feed, the date the tops finally died, and how far from each planting position you actually found tubers. That last measurement is the one nobody keeps and the one that pays back immediately, because it converts directly into next spring's spacing and into how wide you sweep at harvest.
Add a line about the weather in the last six weeks of the season and one about the size grade of what you lifted. Over two or three years, the pattern of warm autumn against tuber size shows up clearly, and it will tell you whether your climate calls for a deeper bed, a sunnier corner, or simply fewer plants given more room each.