Sowing Dates & Soil Temperature

See links below from Harvest to Table.com with plant-specific advice including soil temps.

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

For bok choy planted in the fall or the spring, the optimal soil temperature for direct sown germination is 40-75 F. (4-24 C.). Space the seeds 6-12 inches apart. Keep the bed moist. Bok choy is ready to harvest in 45-60 days. Read more at Gardening Know How: Bok Choy Planting Time: When Do I Plant Bok Choy 


From Harvest to Table.com

CropGermination
Minimum Soil
Temperature (°F)
Germination
Optimum Soil
Temperature
Range (°F)
Germination
Maximum Soil
Temperature (°F)
Days to
Germination
at Optimal
Temps
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
Garlic3565-85957-14
Kale4060-85955-7
Kohlrabi4060-951055-10
Leeks3565-85958-16
Lettuce3560-75852-10
Muskmelon6075-951054-10
Mustard3560-75854-6
Okra6085-951057-12
Onion3565-85954-12
Parsley4065-85955-6 weeks
Parsnip3565-75855-28
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
Zucchini from here70857-10

Below is the above table sorted by Maximum Germination Temperatures for Fall Garden Planning

CropGerminationGerminationGermination Max Soil Temp.
Minimum SoilOptimum Soil
TemperatureTemperature
  Range (°F)
Corn5065-95105
Cucumber6065-95105
Kohlrabi4060-95105
Muskmelon6075-95105
Okra6085-95105
Pumpkin6085-95105
Squash6085-95105
Turnip4060-95105
Watermelon6070-95105
Asparagus5060-8595
Bean, snap6075-8595
Beet4060-8595
Broccoli4060-8595
Brussels sprouts4060-8595
Cabbage4060-8595
Carrot4065-8595
Cauliflower4065-8595
Celery4060-7095
Chinese cabbage4060-8595
Collards4060-8595
Eggplant6075-8595
Garlic3565-8595
Kale4060-8595
Leeks3565-8595
Onion3565-8595
Parsley4065-8595
Pepper6065-7595
Radish4065-8595
Swiss chard4065-8595
Tomato5065-8595
Bean, lima6075-8585
Endive/Escarole3560-7585
Lettuce3560-7585
Mustard3560-7585
Parsnip3565-7585
Pea4065-7585
Radicchio3560-7585
Spinach3565-7575
Zucchini from here7085 

Fall Germination Vs Soil Temps

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:
Days to Maturity (they used varieties recommended for fall/winter)
+ 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)***8/2/2019  
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
Turnip, purple top (DS)9/27/2019  
Lettuce, baby (DS)10/3/20197585
Spinach (DS)10/7/20197075
Turnips, salad (DS)10/8/2019  
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.


From Pam Dawling. Updated and posted in her blog 4/21/2021. These apply to soil temperatures when you sow directly in the ground, and to air temperatures when you sow indoors in small containers.

Pams-Vegetable-seed-germination

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