When to Harvest Sweet Corn: Signs It's Ready to Pick

Sweet corn is the one crop in the plot that refuses to show you its progress. Tomatoes blush, beans dangle, onions flop over — corn wraps its entire harvest in a green parcel and makes you guess. Pick a few days early and you get thin, watery kernels with none of the sugar you grew it for. Pick a few days late and the kernels turn doughy and starchy. The window on any individual ear is only a handful of days wide, which is why late August and September in the vegetable garden means checking the corn patch every single morning.

Counting the days

Seed packets quote days to maturity — roughly 60 to 100 days depending on variety — but that clock starts at sowing and drifts with the weather, so it's only ever a rough guide. The reliable clock starts later, at silking: the day the silks first push out of the top of the ear.

From that day, most sweet corn is ready in 18 to 24 days. Mark the date on the calendar or tie a strip of tape on the stalk when the first silks appear on each plant. Hot, dry weather speeds ripening and can shorten it to a little over two weeks; a cool, dull spell can stretch it beyond four.

The signs from outside

Before you open anything, read the ear from the outside. Four signals appear together on a ready ear:

• The silks have turned brown and dry all the way down to where they meet the husk — not just crisped at the tips.
• The husk is still tight and green. A husk drying to pale straw means you've gone past it.
• The tip of the ear feels full and rounded through the husk rather than tapering to a point.
• The ears begin to angle away from the stalk instead of hugging it, pushed out by their own weight.

If all four line up, it's time for the milk test.

The milk test: how to tell when corn is ready

This is the only method that gives you a definitive answer. Peel the husk back just far enough to expose a few kernels near the tip of the ear — a slit of a few centimetres is plenty — and press a thumbnail into one kernel.

If it needs more time, fold the husk back over the exposed kernels and secure it with a loose elastic band or a twist tie. That keeps birds and earwigs out for the few days that remain.

How to pick

Harvest in the cool of the morning. Sugar levels peak overnight and start falling as the day warms, so a dawn-picked ear is measurably sweeter than the same ear picked at four in the afternoon.

Hold the stalk firmly with one hand — this matters, because you don't want to rock the whole plant — grip the ear with the other, bend it sharply downward and twist at the same time. A ripe ear snaps cleanly off the stalk. Don't saw at it, and never yank upward: you'll tear the stalk and damage the second ear that's still developing lower down.

After picking: the starch clock

The moment an ear leaves the plant, the sugars in the kernels begin converting to starch. With traditional open-pollinated and older hybrid varieties, that conversion is brutally fast — a noticeable loss of sweetness within a few hours, which is exactly why home-grown corn eaten the same day tastes like a different vegetable from shop-bought.

• Cook it the day you pick it whenever you can. If you can't, refrigerate immediately with the husks left on.
• Modern sugary-enhanced (se) and supersweet (sh2) varieties hold their sugar far better and stay good for several days in the fridge.
• Expect one to two usable ears per stalk. The top ear ripens first, typically several days before the one below it.
• For freezing, blanch the ears briefly and freeze the same day — the starch clock doesn't pause on the worktop.

Overripe or underfilled ears

Not every ear will be perfect, and almost all of them are still worth eating.

• Doughy, starchy ears: don't bin them. Cut the kernels off and use them in chowder, corn fritters, or on the grill where the starch caramelises nicely.
• Gappy, half-filled tips: patchy pollination, not a care failure. Corn is wind-pollinated, so next season plant it in a block of at least four rows by four rather than a single long row.
• Tiny secondary ears that will never fill: pick them early as baby corn and stir-fry them whole.
• Ears that never silked at all: usually late sowing or a cold summer — the plant ran out of season.

Keep an eye on the wildlife, too. Birds, badgers and raccoons have a far better sense of when corn is ripe than most gardeners do, and they tend to raid the patch the very week it comes ready. If something has torn into an ear overnight, take that as your signal: the rest are almost certainly ready. Check the patch daily once the silks start browning, and net or fence it if raids become a habit.

One rule above all: don't harvest by the calendar alone. A hot fortnight or a cool cloudy one moves the schedule by a week or more in either direction, and the seed packet knows nothing about your summer. Trust the silks and the milk test over the printed date every time.