Houston’s own frost dates only stretch from February 4 to March 1 in spring and December 1 to 19 in fall, and that’s for one station in the mildest corner of the state. Texas runs across four USDA hardiness zones, so a single sowing calendar for the whole state doesn’t exist. What follows starts from the Houston numbers because they’re the only verified figures available, then explains exactly where and why the picture changes.
The short answer for Texas
At the Houston reference station (IAH), the last spring freeze falls somewhere between February 4 and March 1, and the first fall freeze lands between December 1 and December 19. Those aren’t fixed calendar dates. They mark the window where the National Weather Service’s 1991-2020 climate normals put the probability of a 32°F freeze between 30% and 70%. In plain terms: sow a frost-tender cover crop before February 4 in the Houston area and you’re betting against odds that are still tilted toward frost. Wait past March 1 and the odds have mostly flipped in your favor.
For cool-season cover crops, meaning cereal rye, oats, crimson clover, and hairy vetch, the practical sowing window at this station sits in the weeks before that December freeze window opens, so a September through early-November planting gives the crop enough fall growth before winter dormancy. Warm-season cover crops like cowpeas, sunn hemp, or sorghum-sudangrass want soil that’s already warmed past the spring freeze risk, which points to a sowing window opening after that February 4 to March 1 stretch has passed, typically not before mid-March at the earliest.
Here’s the part that matters most: these are Houston dates, not Texas dates. The coldest month’s mean daily minimum at this station is 43.7°F, a mild figure that tells you winter here rarely delivers a hard, sustained freeze. That number is doing real work in this calendar, it’s the reason cool-season legumes can often be sown later and survive winter without heavy mulch protection near the Gulf. Move north or west and that mean minimum drops fast, which shortens the whole calendar from both ends.
Even inside the Houston metro, the numbers aren’t uniform. Hobby Airport runs about two weeks milder than IAH, the station these figures come from. So a gardener working from this page should treat these dates as a starting estimate for the Gulf Coast corridor, not a fixed schedule, and should expect their own yard to drift a week or two in either direction depending on how close they sit to the coast, to pavement, or to elevation changes.
What will not work here
A cool-season cover crop that needs a long, hard freeze to trigger its winter dormancy cycle properly is working against the numbers at the Gulf Coast end of Texas. With a coldest-month mean daily minimum of 43.7°F, winters here are short on the sustained cold that some northern-bred cover crop varieties are selected around. That’s not a dealbreaker for most legumes and cereals grown as cover crops, but it does mean varieties bred for harder winters may simply keep growing through what should be their dormant season, get caught by a late cold snap, and suffer more damage than they would further north where cold arrives earlier and stays longer.
Sowing a warm-season cover crop too early is the mirror-image mistake. Planting sunn hemp or cowpeas before the last freeze probability has dropped below 30% risks a wasted planting: seed that germinates into a stand of seedlings, then gets knocked back or killed by a freeze arriving inside that February 4 to March 1 window. Because that window represents genuine uncertainty, not a hard cutoff, an early warm-season planting isn’t guaranteed to fail every year, but it’s a bet against the odds, and repeated over several seasons the odds win.
The opposite failure shows up at the other end of the calendar. Sowing a cool-season cover crop too late, after that December 1 to 19 freeze window has already passed, leaves the crop without enough fall growth to establish a root system before cold weather slows everything down. A thin, shallow-rooted stand of cereal rye or clover going into winter is far more vulnerable to freeze damage and winterkill than one that had six to eight weeks of fall growth first.
None of this is really about a state-level heat or drought problem the way it might be in the Panhandle or West Texas. At the Houston reference point, the risk is almost entirely about timing relative to two freeze windows, not about surviving a brutal summer. That’s a very different failure mode than a gardener further inland or further west would face, which is exactly why a single statewide calendar can’t cover both cases honestly.
What changes across Texas
Texas spans USDA hardiness zones 6a through 10a, according to the 2023 USDA Plant Hardiness Zone Map. That’s not a narrow range. Zone 6a describes winters with average annual extreme minimums well below zero, the kind of cold found in the Texas Panhandle. Zone 10a, at the other end, describes winters that rarely drop below the 30s, the kind of climate found along the far southern Gulf Coast and Rio Grande Valley. A four-zone spread inside one state means there is no single planting calendar that honestly applies everywhere, and this page, built on Houston data, sits closer to the 9a/9b end of that range rather than the Panhandle’s 6a-7a end.
What that spread means in practice: a reader gardening further north or at higher elevation than the Houston reference station should expect both frost dates to shift earlier in fall and later in spring, compressing the growing season on both ends. A cool-season cover crop that has until early December to get established near Houston might need to be in the ground weeks earlier further north, simply because the first fall freeze arrives sooner there. The same logic runs in reverse for warm-season crops: a gardener in a colder zone needs to wait longer past their own local last-frost date before the soil and air are reliably warm enough for sunn hemp or cowpeas to thrive rather than sit stalled.
This page can’t tell an individual reader which zone their own yard falls into, and it shouldn’t try to guess from a county name alone, since zone boundaries inside Texas don’t follow county lines cleanly. The USDA’s interactive Plant Hardiness Zone Map is built for exactly this problem: entering a ZIP code returns the zone for that specific location, which is the only reliable way to know whether a garden is closer to the mild Gulf Coast end of this calendar or the much harsher Panhandle end.
Where to check this for your own county
Texas A&M AgriLife Extension, at agrilifeextension.tamu.edu, is the land-grant university extension service covering the entire state, and it’s the right next stop after this page. A state-level calendar like this one, anchored to a single Houston weather station, is a starting point, not a final answer. County extension offices publish planting guidance built from local trial data and local weather records, which will always outrank a state-level estimate for accuracy in a specific yard.
Two things are worth looking for once there. First, a county or regional planting calendar, since AgriLife Extension organizes much of its guidance by county office and by the state’s distinct growing regions, which stretch from the Panhandle to the Gulf Coast to the Rio Grande Valley. A calendar built for a specific county’s own frost data will reflect the local freeze windows far than the IAH station figures used here. Second, look for any cover crop variety trial results specific to that county or region. AgriLife’s research stations across Texas test how specific cover crop species and varieties perform under local soil, heat, and rainfall conditions, and that kind of trialled performance data is more useful than a generic species description.
It’s worth saying plainly: this page describes a statewide pattern built from one reference station’s data, useful for understanding the mechanics of freeze-date probability and how it shapes a cover crop calendar. A county-level recommendation from AgriLife Extension, built from local data and local trials, will be more accurate for any specific garden than anything on this page. Treat this as the framework and the county office as the fine-tuning.
Checking this against your own garden
Every date on this page is a probability built from decades of weather station averages, and no probability replaces what’s actually happening in a specific patch of soil on a specific day. Three simple checks, done by hand and by eye, tell a gardener more about their own microclimate than any calendar can.
Soil warmth by feel is the first and most direct check. Pushing a hand a few inches into the soil in early spring reveals whether it’s still cold and damp, which favors cool-season crops still finishing their cycle, or whether it’s warmed through, which signals it’s safe to sow warm-season species like cowpeas or sunn hemp regardless of what the calendar date says. A yard shaded by trees or sitting in a low, damp spot will lag behind a sunny, well-drained bed by a week or more even on the same property.
The first flush of flowers on a legume cover crop, whether it’s crimson clover or hairy vetch, signals that the plant has shifted from vegetative growth into reproduction, which is useful timing information if the plan is to terminate the cover crop before it sets seed and becomes a weed problem next season.
The appearance of the first true leaves on a newly sown stand, the leaves that emerge after the initial seed leaves and actually resemble the mature plant, confirms that germination succeeded and the crop has moved past its most vulnerable early stage, a more reliable signal of establishment than counting days since sowing.