Jump here to info for annual flower seed germination.
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 both bok choy planted in the fall or the spring, the optimal soil temperature for direct sown germination is 40-75 F. (4-24 C.). The soil should be well draining and rich in organic material. Space the seeds 6-12 inches (15-30.5 cm.) 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
- VEGETABLE SEED GERMINATION SPECIAL REQUIREMENTS
- SEED STARTING SPECIFIC CROPS
- VEGETABLE SEED GERMINATION TEMPERATURES – Table extracted below.
| Crop | Germination Minimum Soil Temperature (°F) | Germination Optimum Soil Temperature Range (°F) | Germination Maximum Soil Temperature (°F) | Days to Germination at Optimal Temps |
|---|---|---|---|---|
| Asparagus | 50 | 60-85 | 95 | 14-18 |
| Bean, lima | 60 | 75-85 | 85 | 4-10 |
| Bean, snap | 60 | 75-85 | 95 | 4-10 |
| Beet | 40 | 60-85 | 95 | 4-10 |
| Broccoli | 40 | 60-85 | 95 | 7-10 |
| Brussels sprouts | 40 | 60-85 | 95 | 3-10 |
| Cabbage | 40 | 60-85 | 95 | 5-10 |
| Carrot | 40 | 65-85 | 95 | 6 |
| Cauliflower | 40 | 65-85 | 95 | 4-10 |
| Celery | 40 | 60-70 | 95 | 10 |
| Chinese cabbage | 40 | 60-85 | 95 | 4-10 |
| Collards | 40 | 60-85 | 95 | 5-10 |
| Corn | 50 | 65-95 | 105 | 4-10 |
| Cucumber | 60 | 65-95 | 105 | 5-7 |
| Eggplant | 60 | 75-85 | 95 | 10-15 |
| Endive/Escarole | 35 | 60-75 | 85 | 10-14 |
| Garlic | 35 | 65-85 | 95 | 7-14 |
| Kale | 40 | 60-85 | 95 | 5-7 |
| Kohlrabi | 40 | 60-95 | 105 | 5-10 |
| Leeks | 35 | 65-85 | 95 | 8-16 |
| Lettuce | 35 | 60-75 | 85 | 2-10 |
| Muskmelon | 60 | 75-95 | 105 | 4-10 |
| Mustard | 35 | 60-75 | 85 | 4-6 |
| Okra | 60 | 85-95 | 105 | 7-12 |
| Onion | 35 | 65-85 | 95 | 4-12 |
| Parsley | 40 | 65-85 | 95 | 5-6 weeks |
| Parsnip | 35 | 65-75 | 85 | 5-28 |
| Pea | 40 | 65-75 | 85 | 5-7 |
| Pepper | 60 | 65-75 | 95 | 7-10 |
| Pumpkin | 60 | 85-95 | 105 | 4-10 |
| Radicchio | 35 | 60-75 | 85 | 5-7 |
| Radish | 40 | 65-85 | 95 | 4-10 |
| Spinach | 35 | 65-75 | 75 | 6-14 |
| Squash | 60 | 85-95 | 105 | 7-10 |
| Swiss chard | 40 | 65-85 | 95 | 7 |
| Tomato | 50 | 65-85 | 95 | 5-7 |
| Turnip | 40 | 60-95 | 105 | 3-10 |
| Watermelon | 60 | 70-95 | 105 | 4-10 |
| Zucchini from here | 70 | 85 | 7-10 |
Fall Germination Vs Soil Temps
The dates in the table below were produced by a spreadsheet calculator from Johnny’s Seeds web site. 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 | |||
| Crop | Plant NLT ** | Opt Soil Temp | Max Soil Temp |
| Brussels Sprouts (TP)*** | 8/2/2019 | ||
| Cabbage, storage (TP) | 8/7/2019 | 85 | 95 |
| Leeks (TP) | 8/7/2019 | 75 | 95 |
| Cabbage, fresh eating (TP) | 9/1/2019 | 85 | 95 |
| Carrots (DS) | 9/5/2019 | 80 | 95 |
| Broccoli (TP) | 9/7/2019 | 85 | 95 |
| Cauliflower (TP) | 9/8/2019 | 80 | 95 |
| Onions (DS) | 9/11/2019 | 80 | 95 |
| Beets (DS) | 9/18/2019 | 85 | 95 |
| Greens, Asian, full size (DS) | 9/23/2019 | ||
| Lettuce, heads (DS) | 9/23/2019 | 75 | |
| Cabbage, Chinese (TP) | 9/24/2019 | 85 | 95 |
| Radish, Daikon (DS) | 9/26/2019 | 85 | |
| Swiss chard, bunching (DS) | 9/27/2019 | 85 | 95 |
| Turnip, purple top (DS) | 9/27/2019 | ||
| Lettuce, baby (DS) | 10/3/2019 | 75 | 85 |
| Spinach (DS) | 10/7/2019 | 70 | 75 |
| Turnips, salad (DS) | 10/8/2019 | ||
| Radish, round (DS) | 10/25/2019 | 80 | 95 |
** 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.
Flower Seed Germination
For which flowers can be sown in the garden go to Iowa State University Page Direct-Seeding Annual Garden Flowers.
The table and paragraphs below were extracted from Annual Flower Seed Germination Guide by Richard Jauron, Iowa State University, Department of Horticulture. But, it does not include Marigold Seed: Marigold seeds generally do not germinate until soil temperatures reach 65 degrees Fahrenheit, though to be safe you should wait until they hit 70 F. 5-10 days to germinate. From SFGate.
| Annual | Germination Temperature (Fahrenheit) | Lighting | Days to Germination | Weeks Sowing to Planting |
|---|---|---|---|---|
| Ageratum (Ageratum houstonianum) | 70-75 | L | 7-10 | 8 |
| Snapdragon (Antirrhinum majus) | 70 | L | 7-14 | 8-10 |
| Wax Begonia (Begonia x semperflorens-cultorum) | 70-75 | L | 14 | 10-12 |
| Annual Aster (Callistephus chinensis) | 70 | L-D | 7-10 | 6-8 |
| Vinca (Cathranthus roseus) | 70-75 | L-D | 14 | 10 |
| Cockscomb (Cleosia spp.) | 70-75 | D | 7-10 | 6-7 |
| Bachelor’s Button (Centaurea cyanus) | 65-70 | L-D | 7-14 | 8 |
| Cosmos (Cosmos spp.) | 70 | D | 5-7 | 4-6 |
| Lisianthus (Eustoma grandiflorum) | 75 | L | 10-14 | 14 |
| Globe Amaranth (Gomphrena globosa) | 70 | L-D | 14 | 7-8 |
| Sunflower* (Helianthus annuus) | 70 | D | 5-7 | 3-4 |
| Strawflower (Helichrysum bracteatum) | 70-75 | L-D | 7-10 | 6-8 |
| Impatiens (Impatiens wallerana) | 70-75 | L | 10-14 | 8-10 |
| Annual Statice (Limonium sinuatum) | 70 | L-D | 7-10 | 8-10 |
| Melampodium (Melampodium paludosum) | 65-70 | L-D | 7-10 | 7 |
| Four-O’Clock (Mirabilis jalapa) | 70 | D | 5-7 | 6-8 |
| Flowering Tobacco (Nicotiana alata) | 70-75 | L | 10-14 | 8 |
| Geranium (Pelargonium x hortorum) | 70-75 | D | 7-21 | 12 |
| Petunia (Petunia x hybrida) | 75 | L | 7-10 | 8-10 |
| Moss Rose (Portulaca grandiflora) | 75 | L | 7-10 | 10 |
| Black-Eyed Susan (Rudbeckia spp.) | 70 | L-D | 7-14 | 10 |
| Red Salvia (Salvia splendens) | 70-75 | L | 10-14 | 8 |
| Mealycup Sage (Salvia farinacea) | 70-75 | L | 10-14 | 8-9 |
| Creeping Zinnia (Sanvitalia procumbens) | 70 | D | 7-10 | 6-7 |
| Coleus (Solenostemon spp.) | 70-75 | L | 10-14 | 8-10 |
| Dahlberg Daisy (Thymophylla tenuiloba) | 65-70 | L | 14 | 8 |
| Nasturtium* (Tropaeolum majus) | 65-70 | D | 10-14 | 5-6 |
| Zinnia (Zinnia elegans) | 70 | D | 5-7 | 5 |
*Sunflowers and nasturtiums do not transplant well. Both should be seeded directly into peat pots.
For Zinnias – The germination process takes about 5-7 days at 75 degrees F. Remember, always keep the soil temperatures above 60 degrees F, ideally at greater than 70 degrees F. From here.
Light conditions during germination are critical for many annual flowers. The seeds of some plant species require light for germination. (In the table above, annuals that require light for germination are designated with the letter L in the lighting column.) After sowing these seeds, lightly press them into the germination medium, but do not cover them. The seeds of other flowers require darkness (D) and should be covered with the germination medium. Finally, those designated L-D should be lightly covered, leaving the seeds as close to the soil surface as possible.
