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:

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.

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

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

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:

"Vegetable Seed Germination," J. F. Harrington and P. A. Minges, California Agricultural Extension Leaflet, 1954.
"Managing Cover Crops Profitably, 3rd Edition," USDA SARE, p.125, 2012.
"Modeling the Effect of Temperature on the Germination Speed in Some Legume Crops," Ahmet Balkaya, Journal of Agronomy, 3: 179-183, 2004.
"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.