Germination Requirements for Annuals and Vegetables

Care and How-To

While gardeners can purchase bedding plants at garden centers and greenhouses in spring, many gardeners prefer to get a head start on the garden season by starting flower and vegetable seedlings indoors. Growing quality seedlings indoors requires high-quality seeds, a well-drained growing medium, containers, proper temperature and moisture conditions, and adequate light.germinating seedling photo by adobestock
 
Germination requirements (light and temperature) vary among annuals and vegetables. The various crops also differ in the length of time from seed sowing until the seedlings are planted outdoors.

More resources on starting seeds can be found in this article: Resources for Seed Starting Indoors.
 
Below is germination and growing information for commonly grown annual flowers, herbs, and vegetables. 


Annuals  |  Vegetables & Herbs  |  Vegetables & Herbs Direct Sown in Garden  |  More Information


Germination Temperature (°F) The ideal air temperature for germination in degrees Fahrenheit.
Once germinated, nearly all seedlings will grow best with daytime temperatures between 65 and 70°F and nighttime temperatures a few degrees cooler.
Light Requirements
for Germination

Light conditions during germination are critical for many annual flowers and vegetables. The seeds of some plant species require light for germination, and others require darkness.

L = Require Light for Germination.  After sowing these seeds, lightly press them into the germination medium, but do not cover them.
D = Require Darkness for Germination. Cover the seed with the germination medium (usually 1/4 to 1/2 inch - precise depth outlined on the seed packet)
L-D = Lightly Cover Seed. Do not place these seeds too deep in the soil. Lightly cover the seed, leaving the seeds as close to the soil surface as possible.

Days to Germination The number of days to expect the seed to germinate and emerge.
Weeks Sowing
to Planting

The number of weeks needed to get seedlings/transplants large enough to plant outside. 

Use this number to determine when to sow seeds indoors.  If you intend to plant outdoors on May 15th, then the sowing date indoors would be the number of weeks listed in this column before May 15th.

Germination Requirements for Select Annuals

  Germination
Temperature
(°F)
Light Requirements
for Germination
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 (Plectranthus scutellarioides) 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

* These species do not transplant well. Should be seeded directly into peat pots.

Germination Requirements for Select Vegetables and Herbs

  Germination
Temperature
(°F)
Light Requirements
for Germination
Days to
Germination
Weeks Sowing
to Planting
Onion 70-75 L-D 4-20 8-10
Dill 65-70 L 7-14 5-6
Kale** 65-70 D 4-7 4-6
Cauliflower 65-70 D 4-7 4-6
Cabbage 65-70 D 4-7 4-6
Broccoli 65-70 D 4-7 4-6
Brussels Sprouts 65-70 D 5-8 4-6
Pepper 70-75 D 7-10 6-8
Watermelon** 75-80 D 3-10 3-4
Muskmelon** 75-80 D 3-10 3-4
Cucumber** 75-80 D 3-10 3-4
Squash and Pumpkin** 75-80 D 5-10 3-4
Tomato 70-75 D 6-12 5-7
Basil 65-70 D 10-14 5-6
Parsley 70-75 D 20-25 6-8
Eggplant 70-75 D 7-10 6-8
Celery 70-75 L-D 14-21 10-12

** Can be successfully (and frequently are) direct sown in the garden in spring when temperatures are warm enough.

Germination Requirements for Select Vegetables and Herbs that are Direct Sown in the Garden

Plant these vegetables directly in the garden in spring when temperatures are warm enough.

  Germination
Temperature
(°F)
Light Requirements
for Germination
Days to
Germination
Beans 70-80 D 8-10
Beets 50-80 D 5-8
Carrots 50-80 D 7-21
Sweet Corn 65-85 D 4-7
Kohlrabi 65-70 D 4-7
Lettuce 60-70 L 7-14
Peas 50-65 D 9-14
Radish 55-75 D 3-4

More Information

Authors: 

Aaron Steil Consumer Horticulture Extension Specialist

Aaron Steil is the consumer horticulture extension specialist at Iowa State University where he works with county Extension offices across the state to answer home gardening questions for all Iowans.  This includes information related to trees, shrubs, vegetables, fruits, herbs, perennials, ...

Last Reviewed: 
December, 2023