Flower Seed Germination

For a list of flowers that 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.

AnnualGermination
Temperature
(Fahrenheit)
LightingDays to
Germination
Weeks Sowing
to Planting
Ageratum (Ageratum houstonianum)70-75L7-108
Snapdragon (Antirrhinum majus)70L7-148-10
Wax Begonia (Begonia x semperflorens-cultorum)70-75L1410-12
Annual Aster (Callistephus chinensis)70L-D7-106-8
Vinca (Cathranthus roseus)70-75L-D1410
Cockscomb (Cleosia spp.)70-75D7-106-7
Bachelor’s Button (Centaurea cyanus)65-70L-D7-148
Cosmos (Cosmos spp.)70D5-74-6
Lisianthus (Eustoma grandiflorum)75L10-1414
Globe Amaranth (Gomphrena globosa)70L-D147-8
Sunflower* (Helianthus annuus)70D5-73-4
Strawflower (Helichrysum bracteatum)70-75L-D7-106-8
Impatiens (Impatiens wallerana)70-75L10-148-10
Annual Statice (Limonium sinuatum)70L-D7-108-10
Melampodium (Melampodium paludosum)65-70L-D7-107
Four-O’Clock (Mirabilis jalapa)70D5-76-8
Flowering Tobacco (Nicotiana alata)70-75L10-148
Geranium (Pelargonium x hortorum)70-75D7-2112
Petunia (Petunia x hybrida)75L7-108-10
Moss Rose (Portulaca grandiflora)75L7-1010
Black-Eyed Susan (Rudbeckia spp.)70L-D7-1410
Red Salvia (Salvia splendens)70-75L10-148
Mealycup Sage (Salvia farinacea)70-75L10-148-9
Creeping Zinnia (Sanvitalia procumbens)70D7-106-7
Coleus (Solenostemon spp.)70-75L10-148-10
Dahlberg Daisy (Thymophylla tenuiloba)65-70L148
Nasturtium* (Tropaeolum majus)65-70D10-145-6
Zinnia (Zinnia elegans)70D5-75

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.

*Sunflowers and nasturtiums do not transplant well. Both should be seeded directly into peat pots.

For 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.

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.

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