When Is Corn Harvested? The Milk Test, Not the Calendar

Sweetcorn has one of the shortest harvest windows of anything in a vegetable garden — often two to four days — and it starts losing sweetness within an hour of being cut.

Which makes it the one crop where the picking decision matters as much as the growing.

The three signs

1. The silks. The tassels emerging from the top of the cob turn brown and dry, usually about three weeks after they first appeared. Green silks mean wait.

2. The feel. Squeeze the cob through the husk. It should feel full and rounded right to the tip, not tapering away. A cob that narrows at the end is not filled.

3. The milk test. This is the decisive one.

Peel back a small strip of husk, pierce a kernel near the top with a thumbnail, and look at what comes out:

Timing is roughly 60 to 100 days from sowing depending on variety, and about 18 to 24 days after the silks first appear — but weather moves both, so the signs override the count.

Why the window is so short

Sweetcorn varieties are bred for sugar content, and that sugar is unstable. The cob passes from underripe through the milk stage into the dough stage in a matter of days, faster in hot weather.

Older standard sugary (su) varieties move fastest. Sugary enhanced (se) and especially supersweet (sh2) varieties hold their sugar longer both on the plant and after picking, which is what supermarket corn relies on.

Pick in the morning, and cook it fast

Sugar begins converting to starch within an hour of picking. In a standard variety, a cob left at room temperature for a day can lose a large share of its sweetness.

This is the entire reason homegrown sweetcorn tastes different from shop corn, and the reason for the old instruction to put the water on to boil before walking out to pick.

Practically:

• Pick in the early morning, when sugar content is highest.
• Cook within hours if you can.
• Refrigerate immediately, in the husk, otherwise — cold slows the conversion substantially.
• Blanch and freeze on the day for longer storage. Corn frozen within hours of picking routinely tastes better than fresh corn that has sat for three days.

To pick: hold the stalk with one hand, grip the cob, and twist downward while pulling. It snaps off cleanly. Do not yank, which can bring the stalk over.

Half-filled cobs

The commonest sweetcorn disappointment, and it is a pollination problem rather than a growing one.

Each silk connects to a single kernel, and every silk needs to catch a grain of pollen for that kernel to develop. A cob with scattered gaps is a cob whose silks were missed.

Corn is wind pollinated, so:

• Plant in a block, at least four rows by four — never a single long row, which pollinates badly whatever its length.
• Tap or shake the tassels on a still, dry morning so pollen falls onto the silks below.
• Do not plant different types close together. Supersweet varieties crossed with standard or popcorn produce starchy, disappointing kernels. Separate them by distance or by sowing date.

What to do with corn you missed

A cob past the milk stage is not wasted:

• Dough stage — still good in soups, chowders and fritters, where texture matters less than sweetness.
• Fully dry on the plant — leave it, and use it for cornmeal, popcorn if it is a popping variety, or save the seed for next year.

And the stalks are excellent compost material once shredded, or a ready-made support for climbing beans in a Three Sisters planting the following season.