Sowing Dates & Soil Temperature

Min/Opt/Max temps from IFAS

MINIMUM Soil Temperature for Germination
  • 32° – Lettuce, Onion, and Spinach
  • 40° – Beet, Broccoli, Cabbage, Carrot, Cauliflower, Parsley, Pea, Radish, Swiss Chard
  • 50° – Sweet Corn, Tomato
  • 60° – Lima bean, Snap Bean, Cucumber, Okra, and Pepper
  • 65° – Squash
OPTIMUM Soil Temperature for Germination
  • 70° – Celery, Parsnip, and Spinach
  • 75° – Asparagus, Endive, Lettuce, and Pea
  • 80° – Lima Bean, Carrot, Cauliflower, Onion, Radish, Tomato, Turnip
  • 85° – Snap Bean, Beet, Broccoli, Cabbage, Parsley, Pepper, Sweet Corn, and Swiss Chard
  • 95° – Cucumber, Okra, Squash
MAXIMUM Soil Temperature for Germination
  • 75° – Lettuce and Spinach
  • 85° – Lima Beans, and Pea
  • 95° – Snap Bean, Beet, Broccoli, Cabbage, Carrot, Cauliflower, Eggplant, Onion, Parsley, Pepper, Radish, Swiss Chard, and Tomato
  • 106° – Cucumber, Okra, Squash, Sweet Corn

About Southern Peas from Clemson.edu

Southern peas are a warm-season crop requiring warm soil temperature (at least 60 °F) for the best germination and emergence. Many pests and diseases will plague Southern peas planted into cool soils. Four to six seeds per foot of row should be planted three-quarters to 1½ inches deep in rows 20 to 42 inches apart.


From Harvest to Table.com

CropMin Temp FOpt TempMax TempDays to Germ. at Opt temp
Asparagus5060-859514-18
Bean, lima6075-85854-10
Bean, snap6075-85954-10
Beet4060-85954-10
Broccoli4060-85957-10
Brussels sprouts4060-85953-10
Cabbage4060-85955-10
Carrot4065-85956
Cauliflower4065-85954-10
Celery4060-709510
Chinese cabbage4060-85954-10
Collards4060-85955-10
Corn5065-951054-10
Cucumber6065-951055-7
Eggplant6075-859510-15
Endive/Escarole3560-758510-14
Kale4060-85955-7
Kohlrabi4060-951055-10
Lettuce3560-75852-10
Muskmelon6075-951054-10
Mustard3560-75854-6
Okra6085-951057-12
Onion3565-85954-12
Parsley4065-85955-6 weeks
Pea4065-75855-7
Pepper6065-75957-10
Pumpkin6085-951054-10
Radicchio3560-75855-7
Radish4065-85954-10
Spinach3565-75756-14
Squash6085-951057-10
Swiss chard4065-85957
Tomato5065-85955-7
Turnip4060-951053-10
Watermelon6070-951054-10

Fall Germination vs. Soil Temps from Johnny’s Seeds

The dates in the table below were produced by a spreadsheet calculator from Johnny’s Seeds website. The calculator determines planting dates for crops to be planted outside, without additional protection, for fall harvest.  All are crops that are frost-tolerant and taste great in cooler weather.

The calculator uses this formula:
Number of Days to Maturity (they used varieties recommended for fall/winter)
+ Days of Average Harvest Period
+ Fall Factor (takes into account the slowing of growth that results from cool weather and short days in fall, amounting to about 2 weeks)
= Days to Count Back from First Frost Date

The Optimum and Maximum Temperatures came from the page at this site that cites the data sources.

Based on the average first frost date of 11/30/2019   
CropPlant NLT **Opt Soil TempMax Soil Temp
Brussels Sprouts (TP)***8/2/201965-8595 
Cabbage, storage (TP)8/7/20198595
Leeks (TP)8/7/20197595
Cabbage, fresh eating (TP)9/1/20198595
Carrots (DS)9/5/20198095
Broccoli (TP)9/7/20198595
Cauliflower (TP)9/8/20198095
Onions (DS)9/11/20198095
Beets (DS)9/18/20198595
Greens, Asian, full size (DS)9/23/2019  
Lettuce, heads (DS)9/23/201975 
Cabbage, Chinese (TP)9/24/20198595
Radish, Daikon (DS)9/26/2019 85
Swiss chard, bunching (DS)9/27/20198595
Lettuce, baby (DS)10/3/20197585
Spinach (DS)10/7/20197075
Radish, round (DS)10/25/20198095

** The date calculated is the date to plant outdoors; crops that should be direct-sown are marked DS. Those marked TP should be set out as transplants on the date shown, so seeds should be started 4 weeks before the planting date.
*** Brussels sprouts should mature after frost, so no additional time is added for the harvest period or fall factor.