Sweet corn is ready 60 to 90 days after planting, and in Mississippi planting waits on the soil, not the calendar. Soil reaches 60 F well after the last frost, which at the Jackson reference station falls between March 6 and March 22. The season before the first fall frost is long enough for 60 to 90 days. The ears themselves tell you which week to pick. After that, the sugar clock starts running. For the full growing picture, see Growing Sweet Corn in Mississippi.
The short answer
The last frost and warm soil are two different days. A night that stays above freezing says nothing about the ground 4 inches down, which trails the air by weeks. The reference figure for the last spring frost is March 6 to March 22, from the NOAA NCEI climate normals for the airport station. Soil hits 60 F later than that. No date for it is published here, so a soil thermometer is the only honest calendar.
Two sources set the floor a little differently. Utah State University Extension says sweet corn needs soil above 60 F. Clemson Extension says: “Do not plant before the soil temperature at the 4-inch depth is at least 50 ºF. Wait to plant extra-sweet varieties until soil temperatures reach 65 °F.” The two numbers are not interchangeable. Ordinary sweet corn tolerates the lower one, but extra-sweet (sh2) seed sown into 50 F soil tends to rot instead of sprouting. That is why a gardener can do fine one year and lose the whole row the next after switching seed. Keep the depth in mind too: a reading at the surface runs warmer and sends you out early.
Does the season hold 60 to 90 days? Easily. The first fall frost at the same station lands between November 7 and November 22, which leaves more than seven months between the two frost ranges. One caution: those are reference-city figures. Suburban and rural gardens usually see the last spring frost later and the first fall frost earlier, often by one to two weeks, and more at elevation. Check your own county. Sowing dates are covered in When to Sow Sweet Corn in Mississippi.
Two clocks, not one
The 60 to 90 days run from planting. They tell you whether a variety fits the season, nothing more. A second clock, roughly 17 to 24 days from silk emergence, points to the week the ears are ready. Do not blend the two numbers into one.
To pick on the right day, read three signs together: dry brown silks, husks still moist and green, and milky juice when you puncture a kernel. Any one alone misleads. Silks can brown on an ear that is still underfilled, and a green husk says little about the sugar inside.
How fast it fades
Clemson Extension puts the problem plainly: “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.” Five days is a ceiling under ideal conditions, not a promise. Heat is the accelerator, and the Jackson reference station averages 71.1 days a year at 90 F or more. A warm kitchen counter is a poor place for an ear.
Genotype changes the pace. Standard su types lose sugar fastest, se types hold it longer, and sh2 holds it longest. If your harvests tend to sit in a hot car or on the counter before dinner, that is the practical reason to lean toward sh2, keeping its 65 F soil requirement in mind.
Does a late variety fit here?
Yes, a late variety fits here. But the question has two halves, because the frost window and the heat load pull in different directions.
A 60-day variety
A 60-day type is the easy case. Plant once the soil has warmed, and the ears arrive about two months later, long before the fall frost range of November 7 to November 22 comes into play. Even if a cool spring holds the soil under 60 F for several extra weeks, the arithmetic still works with room to spare.
That margin is useful. It lets you stagger plantings so the ears do not all ripen in the same week. Staggering also helps keep different corn types from tasselling together, which matters for a reason covered below.
The real pressure comes from heat, not frost. A short-season crop usually matures in the thick of summer, where 90 F days stack up. Ears picked in the morning and chilled quickly keep more of what the kernel has.
A 90-day variety
A 90-day type fits as well, which is not what a Northern gardener would expect. Count back 90 days from November 7, the early end of the fall frost range, and you land in early August. That is arithmetic, not a planting tip. A spring planting made into warm soil is nowhere near that edge, even after subtracting one to two weeks for a rural garden that frosts early.
What a late type costs is time in the field. More weeks standing in the garden means more weeks of exposure to whatever eats corn here, a subject covered in What Eats Corn in Mississippi, and When. If you choose a 90-day extra-sweet, it also carries the 65 F soil requirement, so it cannot go in as early as an ordinary type and the ears move later into the season.
What goes wrong here
Three failures account for most disappointing rows. Two come from the climate and the calendar. The third has nothing to do with weather.
- Soil sown too cold. Seed sits in ground that is too chilly, then rots or comes up in patches. The remedy is a thermometer at the 4-inch depth, not a date. Use at least 50 F for ordinary sweet corn and 65 F for extra-sweet, and let Utah’s 60 F reading be your cue that the soil is truly warm. A mild March week means little, since soil warms well after the last frost.
- A variety too late for the season. In spring this rarely bites in Mississippi, because 60 to 90 days fit comfortably. It happens when sowing slides into summer. Count the days to maturity forward from planting and check them against the first fall frost range of November 7 to November 22, then pull that date earlier by one to two weeks if you garden inland or at elevation. Choose a shorter type when the margin is thin.
- Sweetness lost to the neighbors. Climate plays no part here. If su, se and sh2 types tassel at the same time, the sweet kernels come out starchy and dull. The remedy is timing: stagger plantings so different types do not tassel together, or grow just one type in a season. Plant each type in a block of three or more rows, a shape of garden rather than a date, instead of a single long row.
No separating distance is published in the Utah State University Extension guidance, so none appears here. What the source does state is the condition: the problem occurs when the types tassel at the same time. Build your plan around that, and around keeping the types apart in the garden.
Common questions
Can I plant sweet corn right after the last frost?
Not by that rule alone. Soil warms well after the last frost. Check the temperature at 4 inches: at least 50 F for ordinary sweet corn, and 65 F for extra-sweet types. Utah State University Extension puts the general figure at above 60 F.
How do I know an ear is ready to pick?
Look for three signs together: dry brown silks, husks still moist and green, and milky juice from a punctured kernel. As a rough guide, the pick week arrives about 17 to 24 days after silk emergence. That clock is separate from the 60 to 90 days counted from planting.
How long does picked corn stay sweet?
Clemson Extension says sweet corn can be stored under optimal conditions for about five days, “but will lose sweetness with each day of storage.” Five days is a maximum, not a guarantee. Heat speeds the loss, and su types fade fastest, se holds longer, and sh2 longest.
Can I grow su, se and sh2 corn in the same garden?
Yes, as long as they do not tassel at the same time. The source gives no isolation distance, so rely on timing and separate plantings, with each type in a block of three or more rows. If the types shed pollen together, the sweetness is lost.