When to Plant Cucumbers: Wait for Warm Soil, Finish Before Frost

Sow cucumbers outdoors after the danger of frost has passed and the soil has warmed to about 65°F, which in a typical US ZIP code is late May, about five weeks after the median last frost. For a fall crop, the last sowing date is about 83 days before your median first frost. In Chicago that is May 26 to August 14; in Dallas it is April 7 to September 7.

Most guides say to wait two weeks after the last frost. We tested that against NOAA 1991–2020 normals¹ for 37,563 lower-48 ZIP codes, set six published local calendars beside our dates, and built spring dates for 24 cities and fall dates for 20. Everything uses air temperature as a stand-in for soil temperature, because our NOAA data has no soil readings.

Spring cucumber sowing dates for 24 cities

Cucumbers are tender: Clemson says light frosts can kill them and that seed will not germinate in soil below 50°F.³ The published start rules differ. The Old Farmer’s Almanac says to sow no earlier than two weeks after the last frost, or when the soil is around 70°F,¹³ and Bonnie Plants gives the same two weeks.¹⁴ Iowa State puts it this way:²

soil temperatures have warmed to 60 to 70°F

Utah State says 65°F,⁴ and the Almanac says to move transplants out only when nights stay above 50°F.¹³ Each date below is the latest of three: our 10% last-frost date, the day the normal daily mean air temperature reaches 65°F, and the day the normal daily low reaches 50°F.

Frost, warm soil or warm nights: which rule sets the date

Warmth, not frost. Across the 36,271 ZIP codes whose normals reach both lines, the 65°F mean sets the date in 94.2%, the 50°F night in 4.9% and the frost date in only 0.9%. Our date falls a median 37 days after the median last frost (middle half 33 to 42), so the two-weeks-after rule is earlier than ours in all but 7 of those ZIP codes, by a week or more in 99.4%. Cities show the same pattern: Chicago’s date is 32 days later than the two-week rule, Boston’s 49 and Salt Lake City’s 41.

The result does not hinge on the 65°F line. At Iowa State’s lower 60°F end, the two-week rule is still earlier than the warmth rules in 99.9% of ZIP codes, and by a week or more in 83.0%. At 70°F, the line Clemson and the Almanac use, our date moves a median 19 days later and 15.4% of ZIP codes never reach it. Air is not soil: soil can lag a cold spring, so measure it. Utah State says seed germinates in 5 to 10 days at 65 to 85°F.⁴

Temperature rules compared across nine sources

Oregon State’s germination table shows why the line sits near 65°F: cucumber seed shows little or no germination at 50°F, takes 13 days to appear at 59°F, 6 days at 68°F and 3 at 86°F.⁶ Table 2 sets the published limits side by side and the chart puts them on one scale.

Early cucumbers are ready in about 50 days at 75 to 85°F, Oregon State says, and late varieties in up to 70.⁵ Utah State adds that hot temperatures reduce fruit set.⁴ Heat is rarely the planting problem. A normal July high of 90°F or more occurs in 27.0% of ZIP codes and 95°F or more in 5.5%.

Direct sow or transplant

Sources start seed indoors two to six weeks ahead: Iowa State, Clemson and Oregon State say two to three weeks,^2,3,5 Maryland three,⁸ Virginia Tech three to four in peat pots⁷ and Utah State four to six.⁴ Transplants buy a little time:

Transplants mature about 2 weeks before seeded cucumbers.

Iowa State sets plants out at one or two true leaves, after hardening them outdoors for a few days.² UF/IFAS does not recommend transplanting cucumbers at all.⁹ Indoor start dates are on our seed-starting guide; set plants out on the dates in Table 1, not earlier.

Covers and a second sowing

Warm-up tricks move the date only so far. Utah State says plastic mulch and row covers allow setting seed or plants out 2 to 3 weeks before the last frost, and advises checking the temperature under a cover with a thermometer, venting when air temperatures pass 80°F and removing covers when plants flower or the air under them passes 90°F.⁴ The dates in Table 1 assume no cover.

A second sowing is worth planning. Virginia Tech says a crop planted around July 1 has fewer disease problems than an early planting kept going until frost,⁷ and Iowa State says plantings made after mid-June are less likely to be damaged by cucumber beetles, because fewer adult beetles are around.² A July 1 sowing fits inside our 83-day count-back in all but 2.4% of ZIP codes.

Fall cucumbers: the last sowing date

A fall crop starts when summer crops finish and ends with frost, which kills the vines. Our last sowing date is 83 days before the median first 32°F frost: 55 to 65 days to maturity, plus 14 for slower fall growth and 14 for a frost-tender crop, the same count-back as the cucumber row of our fall vegetable planting guide. Cornell Cooperative Extension in Warren County, New York, lands close by, listing cucumbers 12 and 11 weeks before a first killing frost.¹² Google’s AI Overview for “when to plant cucumbers for fall harvest” counts back 50 to 70 days when we checked on October 14, 2026; that leaves first fruit only about 15 days before the median frost, and half of years are colder than the median.

Dates in the table are the last day to sow, not the best day. Across all ZIP codes the median last sowing date is August 2; it has passed by August 1 in 45.2%, by August 15 in 73.5% and by September 1 in 91.6%. The median window from our spring date to the last sowing date is 70 days, under 30 days in 12.3% and over 100 in 25.4%.

Why the margin: Rutgers Cooperative Extension names daylength, heat units and frost as the three main fall factors, and says lower temperatures and shortening days make a few days of planting date matter:¹¹

make a big difference in days to maturity in the fall

The cooling is visible in the normals. On the last sowing date the median normal daily mean is 74.2°F, but 55 days later, when the first fruit is due, it is 63.0°F, below 65°F in 80.2% of ZIP codes and below 60°F in 14.5%. A sowing on July 10, Iowa State’s last practical date and the start of Delaware’s window, fits inside the count-back in 92.7% of ZIP codes, and August 7, the end of Delaware’s window, in 40.8%.

How published local calendars compare

Six places have published dates we could convert, nine in all. Our spring dates sit inside the University of Georgia’s and UF/IFAS’s months and nine days after Iowa State’s mid-May. The fall dates are less uniform, as a single count-back should be: Iowa State’s July 10 is 19 days earlier than ours, Cornell’s July 17 to 24 is later than our July 8, the University of Georgia’s August 31 is 12 days later than ours,¹⁰ and Delaware’s window ends 6 days before our date. Maryland’s “second crop around July 1” is a recommended date, not a deadline.⁸

Hot summers, mild winters and frost-free ZIP codes

In the Gulf and Texas cities a normal July high of 90°F or more runs from June through September (Dallas, Austin) or June to August (Houston, Gainesville). Our spring dates there are in March and April, and the fall dates run to September and October. UF/IFAS gives north Florida February to April and again August and September, and central Florida January to March and September.⁹ Frost-free ZIP codes have no frost count, so use the months: the normal mean stays at or above 65°F from March through November in Phoenix (ZIP 85001) and in all twelve months in Miami (33101), but in none in San Francisco (94103). Our table has no frost dates for 104 of Hawaii’s 135 ZIP codes, so we give no Hawaii dates; ask your county extension office.

How we calculated these dates

Daily temperatures are NOAA’s monthly normals placed on the 15th of each month and interpolated linearly, for the station nearest each ZIP code.¹ Frost dates are the median and 10% 32°F dates. The 65°F and 50°F lines are the published rules above, applied to air temperature, not soil. Individual years vary by weeks, and a warm or cold spring will move every date.

Next steps

Look up your own dates with our frost date lookup and read what a last frost date means. Cucumbers wait for the same warm nights as tomatoes, and green beans use a lower 60°F soil line. Cover young vines when a late frost is forecast using our frost-cover guide, and see more crops in our vegetable guides.