Sweet corn is ready when the silks at the ear’s tip have dried brown, the husk is still green and moist, and a punctured kernel gives milky juice. All three together. Where Wyoming’s short season allows, that moment lands roughly from late July into September, depending on when the seed went in and how long the variety takes. Then the sugar starts leaving the kernel, so picking time and eating time need to sit close together.
When sweet corn are ready in Wyoming
Watch the silks, not the calendar: ears are ready once those silks have gone dry and brown. As a rough window, that puts picking from late July into September for plantings that fit the season, with the exact week set by planting date, variety and how warm the summer runs.
What does the Wyoming season allow for sweet corn?
NOAA NCEI climate normals put the mean last spring frost at the reference station between May 7 and May 18, and the mean first fall frost between September 24 and October 5. The reference station has about 130 frost-free days between those two dates, and that is at roughly 6,000 feet. Frost is possible in any month at higher elevations, so a gardener up the mountain has less room still.
The last frost date is not the planting date. Utah State University Extension says sweet corn needs soil above 60 F, and soil reaches that well after the last frost. Clemson Extension adds the depth: do not plant before the soil temperature at the 4-inch depth is at least 50 ºF, and wait to plant extra-sweet varieties until soil temperatures reach 65 °F. Ordinary sweet corn and extra-sweet corn do not share a threshold, so a supersweet seed sown on the ordinary one is a common reason a bed that worked one year fails the next.
The second clock is the one printed on the seed packet. Utah State gives 60 to 90 days from planting, and every one of those days has to finish before the first fall frost. A variety at the long end of that range may not fit a cold, high garden at all. The details of timing a sowing are in When to Sow Sweet Corn in Wyoming, and the broader picture is in Growing Sweet Corn in Wyoming.
How do you tell sweet corn is ripe?
Use three signs at once. The silks should be dry and brown, the husk should still be moist and green, and a kernel punctured with a thumbnail should spurt milky juice. Brown silks alone can mean an ear that is not yet filled out. Clear juice points to an ear that is early, and a doughy paste points to one that is late.
Sweetness also depends on the neighbors. Utah State warns that sweetness is lost if su, se and sh2 types tassel at the same time, and it recommends planting in blocks of three or more rows. The source gives no distance. The working rule is to keep types from tasseling together by staggering them or leaving them out of the same patch. Raccoons and birds often find ripe ears about when you do, which is covered in What Eats Corn in Wyoming, and When.
Keeping them, and for how long
Clemson Cooperative Extension puts the problem in one line: “Sweet corn loses sugar from the kernel rapidly at high temperatures… Sweet corn can be stored under optimal conditions for about five days, but will lose sweetness with each day of storage.” That is where the old advice to run from the garden to the pot comes from. The sugar is already draining the moment the ear is picked, and heat speeds the drain.
How long does picked sweet corn stay sweet?
The ceiling is about five days, and it applies only under optimal conditions. A kitchen counter in August is not optimal. A fridge that is too warm is not optimal either. Treat five days as the most you could hope for and plan on eating the corn much sooner. The phrase “will lose sweetness with each day” matters as much as the number. Day one is better than day two, and day two is better than day five.
The practical routine follows from the mechanism. Pick when the three ripeness signs agree, get the ears into the cold quickly, and leave the husks on until you cook them. If you cannot eat the whole harvest within a few days, cut the kernels off and freeze them rather than letting a pile of ears sit and fade. A patch tends to ripen all at once, so plan for it. A planting that ripens in one week produces far more corn than a household eats in five days.
Does the type of sweet corn change how fast it fades?
Yes, and it is the most useful reason to choose one type over another. The su type loses sugar fastest. The se type holds its sugar longer, and the sh2 type holds it longest. A gardener who wants corn that tolerates a few days in the fridge, or a trip to a farmers’ market, has a good reason to lean toward se or sh2 types.
There is a trade-off in the ground. Clemson says extra-sweet varieties should wait until the soil at the 4-inch depth reaches 65 °F, while ordinary sweet corn can go in at 50 ºF. In a place with a 130-day frost-free window, an sh2 type has fewer days to work with, because its planting date moves later while the first fall frost stays put. Counting the 60 to 90 days from planting against the fall frost range of September 24 to October 5 comes first. Holding quality in the fridge comes second.
Where in the house that actually is
The figures above describe a fridge better than they describe most rooms in a house. A heated kitchen or living space is too warm, and sugar leaves the kernel quickly at high temperatures. A garage swings with the weather. In Wyoming a September garage can be cold overnight and warm by afternoon, and the reference station still averages 10.4 days a year at 90 F or more. On a day like that, a closed garage or a car trunk is a heat trap.
Which room in the house keeps sweet corn coldest?
The refrigerator comes closest, and it is the only spot that stays cool day and night. Put the ears on a shelf with the husks on, away from the door. The door swings the most in temperature each time it opens, and a full shelf is steadier than an empty one. A cool basement or cellar may help for a few hours before you can get to the fridge, though it is not a replacement for one.
A domestic fridge can also run colder than some crops tolerate, especially at the back wall or in a crisper set to its coldest. Sweet corn is more forgiving of cold than of warmth, but it is still a good idea to know what your own shelf is doing.
What should a thermometer tell you?
Put a thermometer on the shelf where the corn will sit and read it before harvest, not after. Skipping the check costs you sweetness quietly, because a fridge that runs a few degrees too warm will not show it until the corn tastes flat on day three. Leave the thermometer in for several hours, then check a different shelf and compare.
For a garage or cellar, read it at the hottest part of the afternoon and again at dawn. If the afternoon reading climbs well above the fridge, that space is for staging, not storing. For anything the household will not eat in a few days, the freezer is the better answer than any shelf.
Common questions
How many days from silks to pick?
Confirm with the three signs: dry brown silks, moist green husks and milky juice from a punctured kernel. The silk clock tells you which week to start checking. The packet’s 60 to 90 days from planting is a separate clock that says whether the crop fits the season.
How long can sweet corn sit after picking?
Clemson Extension says sweet corn can be stored under optimal conditions for about five days, but it will lose sweetness with each day of storage. That is a maximum under good conditions. For the sweetest ears, eat them the day you pick them.
Does a frost end the sweet corn season?
Frost ends the plant’s season, so ears that are not filled out by then will not catch up. The mean first fall frost at the reference station falls between September 24 and October 5, and frost can come any month at higher elevations. If a cold night is forecast while ears are close, the county extension office can tell you what is practical for your elevation.
Which type of sweet corn fades slowest?
The sh2 type holds sugar longest, the se type is in the middle, and the su type loses sugar fastest. Each type has its own soil temperature floor, so an sh2 type also needs warmer soil at planting. Keep types from tassel timing together, and plant in blocks of three or more rows for good pollination.