Sowing Dates & Soil Temperature

Snow Peas

  • From Cornell – Germination temperature: 40° F to 85° F – Optimum around 75° F.
  • Pam Dawling said soil temp optimal is 75° and max is 95°
  • Sep 2021 – Oregon Giant germinated well in the little garden next to fence with soil in the how 90°s.

Bok Choy

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 


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

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
Zucchini70857-10

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

CropGermination Minimum Soil Temperature (°F) Germination Optimum Soil Temperature Range (°F) Germination Max Soil Temp. (°F)
Corn5065-95105
Cucumber6065-95105
Kohlrabi4060-95105
Muskmelon6075-95105
Okra6085-95105
Pumpkin6085-95105
Squash/Zucchini6085-95105
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

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)***8/2/201965-8595 
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.


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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