Days Required for Vegetable Seedling Emergence at Various Soil Temperatures

A basic understanding of the science of biology is critical to successfully partner with nature and produce non-native plant species in our gardens and years. Soil thermometers are relatively inexpensive and a wise investment.
Soil Temperature (degrees Fahrenheit)


Vegetable 		32

41

50

59

68

77

86

95

104
Artichoke - - - - - 14-21 - - -


Asparagus 		NG

NG

53

24

15

10

12

20

28
Bean, Fava - - - 7 7 - - - -


Bean, Green 		NG

NG

NG

16

11

8

6

NG

NG


Bean, Lima 		-

-

NG

31

18

7

7

NG

-


Beet 		-

42

17

10

6

5

5

5

-


Broccoli 		-

-

20

10

6

5

5

-

-


Cabbage 		-

-

15

9

6

5

4

-

-


Cantaloupe / Muskmelon 		-

-

-

-

8

4

3

-

-


Carrot 		NG

51

17

10

7

6

6

9

NG


Cauliflower 		-

-

20

10

6

5

5

-

-


Celery 		NG

41

16

12

7

NG

NG

NG

-


Corn (Maize) 		NG

NG

22

12

7

4

4

3

NG


Cucumber 		NG

NG

NG

13

6

4

3

3

-


Eggplant 		-

-

-

-

13

8

5

-

-


Lettuce 		49

15

7

4

3

2

3

NG

NG


Okra 		NG

NG

NG

27

17

13

7

6

7


Onion 		136

31

13

7

5

4

4

13

NG


Parsley 		-

-

29

17

14

13

12

-

-


Parsnip 		172

57

27

19

14

15

32

NG

NG


Pea 		-

36

14

9

8

6

6

-

-


Pea, Southern 		- - 14 10 8 7 - - -


Pepper 		NG

NG

NG

25

13

8

8

9

NG


Pumpkin 		-

-

-

-

15

6

4

3

-


Radish 		NG

29

11

6

4

4

3

-

-


Soybean 		NG NG NG NG - 7 7 - NG


Spinach 		63

23

12

7

6

5

6

NG

NG


Squash 		-

-

-

-

15

6

4

3

-


Swiss Chard 		-

-

20

15

12

10

7

NG

-


Tomato 		NG

NG

43

14

8

6

6

9

NG


Turnip 		NG

NG

5

3

2

1

1

1

3


Watermelon 		-

NG

-

-

12

5

4

3

-
NG = No Germination - = Not Tested


Notes:
  1. Germination is a complex biological process triggered by environmental conditions specific to the species, and even by cultivar. Temperature is but one of the variables.

  2. Cooler soil temperatures cause seeds to remain dormant increasing their vulnerability to disease, insects and animals.

  3. More days are required with deeper seeding because of cooler temperatures and the greater distance of growth. Sowing too deep can also prevent germination.

  4. Optimal germination temperature is not necessarily the optimal field sowing temperature. For example, many brassicas germinate quickly at higher temperatures but if you wait until these climate conditions occur, the plants will be growing at the wrong time of the season.


References:
  1. "Vegetable Seed Germination," J. F. Harrington and P. A. Minges, California Agricultural Extension Leaflet, 1954.
  2. "Managing Cover Crops Profitably, 3rd Edition," USDA SARE, p.125, 2012.
  3. "Modeling the Effect of Temperature on the Germination Speed in Some Legume Crops," Ahmet Balkaya, Journal of Agronomy, 3: 179-183, 2004.
  4. "Comparative Germination Responses of Cowpea and Maize Genotypes to Soil Moisture Content," Abayomi, Y.A. and Adeniyi A.M., Agrosearch Vol. 7 (1&2) 2005: pp. 34-42.