Sow fall cover crops before the first hard freeze, and spring or summer ones after the last. In Missouri that makes early autumn the main sowing season, with a smaller one in April. The dates move with region and with the year, so treat the ones below as a starting band, not a deadline.
The short answer for Missouri
For the Kansas City reference station, the last spring freeze falls between April 6 and April 20, and the first fall freeze between October 18 and October 29. Fall cover crops go in ahead of the October window. Spring-sown ones start as the April window opens, and tender species wait until it has closed.
Those dates are a probability, not a calendar entry. They come from the NOAA 1991-2020 Climate Normals and describe 32°F freeze probabilities: the stretch of days when the odds of a freeze sit between 30 and 70 percent. The band is the middle of the odds, not the edges. A freeze can land before it or after it. You can see the underlying numbers in the NOAA station normals.
| Event | Window (Kansas City reference station) | What it is a probability of |
|---|---|---|
| Last spring frost | April 6 to April 20 | 32°F freeze odds in the 30-70% band |
| First fall frost | October 18 to October 29 | 32°F freeze odds in the 30-70% band |
One caution on the station. It sits at MCI, well north of the city. The downtown station runs about five days earlier in spring, and southern Missouri is milder still, so a gardener there should expect the spring dates to come earlier than the band above.
Fall sowing
Work backward from October 18. A cover crop needs time to root and put out leaves before the ground freezes, and that time has to be in the bank before the window opens, not spent inside it. With today being October 11, 2026, the window is about a week away. Fast, frost-hardy grains can still go in right now. Anything that establishes slowly is already behind.
Spring and summer sowing
Frost-tolerant species can go in as the April 6 to April 20 band opens, as soon as the soil can be worked. Heat-loving covers such as buckwheat or cowpeas should wait until the band is behind you, and a few days beyond it is safer than a few days short. April 20 is not a guarantee of safety. For species that frost kills outright, the cost of guessing early is a full reseeding. The cost of waiting a week is close to nothing.
For which species fit each window, see The Best Cover Crops for Missouri. For the wider picture of why gardeners use them at all, the Cover Crops for Missouri Gardens guide covers it.
What will not work here
Tender cover crops sown in fall are the first failure. Buckwheat, cowpeas and similar warm-season species die at the first freeze, and with that freeze due between October 18 and October 29, a late-September sowing barely has time to flower, let alone build biomass. The seed packet may say “fall planting,” but it usually means a milder climate than this one.
Late sowing of slow species is the second. Seed scattered on October 25 sits inside the freeze window with maybe days of growth ahead of it. Clovers and vetches sown that late often show up in spring as thin, patchy stands. Hardy cereal grains tolerate the delay far better, which is why they dominate late-season recommendations in the Midwest.
Reading the cold number too literally is the third. The coldest month in the Kansas City normals has a mean daily minimum of 19.5°F. That is an average of the coldest nights, not the record low and not the extreme. Winter hardiness is decided by the worst nights, and the hardiness zone figure (built on average annual extreme minimum temperature) tells you those run colder than 19.5°F. Species rated for milder winters will survive in a typical year and fail in a hard one. In a state that spans zone 5b to 7b, that gamble gets worse the farther north you garden.
Treating the frost band as a date is the fourth mistake. Someone who sows a spring warm-season cover on April 21 because “the last frost was April 20” is reading the table wrong. The band marks where freeze odds fall between 30 and 70 percent. It does not mark where they hit zero. The same logic applies in fall, where “first frost October 29” does not mean October 28 is safe for tender species.
Borrowing dates from the wrong place is the last. The reference station is north of the city, so a gardener in the southern part of the state who follows the Kansas City spring dates to the day may be sowing later than needed. A gardener downtown who does the same is running about five days behind the downtown record.
What this page cannot say: it has no summer heat or rainfall figures for Missouri, so it makes no claim about summer-sown covers failing in drought or humidity. The reasoning above comes only from the frost and winter-cold data.
What changes across Missouri
Missouri is not one garden. The USDA Plant Hardiness Zone Map (2023 edition, built on 1991-2020 normals) places the state across zones 5b to 7b. That is two full zones apart, and the zone system rests on one variable only: the average annual extreme minimum temperature. So there is no single answer for the state, and the Kansas City dates on this page describe one place in the middle of a wide spread.
In the north, the cold arrives sooner and goes deeper. A gardener there should shift fall sowing earlier than the Kansas City band suggests, favor the hardiest species, and avoid cover crops that are borderline for colder winters. Spring sowing slides later as well, since the last freeze comes after the April 6 to April 20 band at the colder end.
In the south, the calendar loosens. Spring comes earlier than the Kansas City station shows, fall freeze tends to arrive later, and species that are marginal farther north become reasonable choices. The reverse risk shows up too, because a mild start to spring can tempt gardeners to sow tender covers before a late freeze.
Terrain matters inside any one zone. Low spots and river bottoms collect cold air on still nights, and ridge tops and south-facing slopes run warmer. A hill that sits a few hundred feet higher can be a week behind or ahead of the valley below it, regardless of what the map says.
This page will not tell you which zone you are in. Look up your own location on the USDA Plant Hardiness Zone Map, then use the north-or-south adjustments above as a direction of travel, not a precise offset.
Where to check this for your own county
Your state extension service is the next stop. University of Missouri Extension runs county offices across the state, and its staff know what grows in local soil and what the local frost pattern looks like. Two things are worth looking for there: the planting calendar for your county, and the cover crop varieties that have been trialled in your county or the nearest one.
A county recommendation beats a state one, and this page is the state one. It rests on a single reference station and a single hardiness range. An extension agent who has watched a hundred local plots knows things a 30-year climate normal cannot, such as which fields hold frost, which clay soils stay cold, and which seed lots have performed.
The page does not have a Missouri-specific cover crop calendar from the extension service to quote. The extension calendars on file for this topic are Clemson Cooperative Extension lawn maintenance calendars (tall fescue, bermudagrass, zoysiagrass), written for another state and another purpose. They are not used here, and a gardener should not stand in for the other. Where a number on this page is missing, the right move is to ask your county office, not to fill the gap from somewhere else.
Checking this against your own garden
Your own observations outrank every date above. Three are worth watching, and none needs equipment.
- Soil warmth by feel. Push a bare hand a few inches into the bed in the morning. Soil that feels cold and stays that way is running behind the calendar, and warm-season covers should wait. A bed that feels mild early tells you the spot is a warm pocket.
- The first male flowers on squash. Male blooms appear before female ones, so the first flush marks real warmth reaching your plants. If yours open a week after a neighbor’s, your garden runs cooler, and spring sowing dates should slip the same way.
- The first true leaves on fall seedlings. The first pair of leaves is the seed’s storage. The second set, the true leaves, means the plant is feeding itself. Seedlings that have true leaves before the freeze window generally overwinter. Seedlings still at the first pair tell you that your sowing was late for your own microclimate.
Write the dates down for a season or two. A garden that always freezes before the Kansas City band has told you something no map will.
Some gardeners also time this by the Moon: when to plant cover crops by the moon, as almanac tradition rather than fact.
Common questions
Is it too late to sow cover crops in Missouri in mid-October?
Not necessarily. The first fall frost window runs October 18 to October 29, so hardy, fast-establishing grains can still go in now. Slow species and tender ones are a poor bet. The earlier in the week you sow, the better the odds that seedlings reach their true leaves before the freeze.
Can I sow after the first frost?
Seed will not germinate well once the ground is frozen, and seedlings that have not rooted will struggle. A light freeze on a still-workable bed is not the end of sowing for the hardiest species, but expect a thin stand. For tender covers, frost ends the season.
Do the Kansas City dates apply across the state?
Only roughly. The reference station sits well north of the city, the downtown station runs about five days earlier in spring, and southern Missouri is milder still. The state spans USDA zones 5b to 7b, so shift your dates toward the colder or milder end depending on where you garden.
What do the frost dates actually mean?
They are NOAA 1991-2020 probabilities for a 32°F freeze, in the 30-70% band. A freeze can still arrive before or after those dates. Use them to plan, then adjust by watching your own soil and plants.