The following chart offers the optimum germination temperature of more than 50 annual flowers. They’ll probably germinate at somewhat lower and somewhat higher temperatures than those given, but germination can then be slow or sporadic and the seedlings may fail to thrive or succumb to soil diseases.
| Annual | Optimal Germination Temperature |
| Ageratum (Ageratum houstonianum) | 70-75 °F (21-24 °C) |
| Alyssum, Sweet (Lobularia maritima) | 55-70 °F (13-21 °C) |
| Amaranth (Amaranthus caudatus) | 70-75 °F (21-24 °C) |
| Amaranth, Globe (Gomphrena globosa) | 68-75 °F (20-24 °C) |
| Angelonia (Angelonia angustifolia) | 70-75 °F (21-24 °C) |
| Aster, China (Callistephus chinensis) | 65-70 °F (18-21 °C) |
| Bachelor’s Button (Centaurea cyanus) | 65-70 °F (18-21 °C) |
| Begonia (Begonia spp.) | 70-75 °F (21-24 °C) |
| Black-Eyed Susan (Rudbeckia spp.) | 70-75 °F (21-24 °C) |
| Black-Eyed Susan Vine (Thunbergia alata) | 65-75 °F (18-24 °C) |
| Browallia (Browalllia spp.) | 65-75 °F (18-24 °C) |
| Calibrachoa, Million Bells (Calibrachoa × hybrida) | 70-75 °F (21-24 °C) |
| Canna (Canna spp.) | 70-85 °F (21-30 °C) |
| Castor Oil Plant (Ricinus communis) | 70-75 °F (21-24 °C) |
| Cathedral Bells (Cobaea scandens) | 70-75 °F (21-24 °C) |
| Celosia (Celosia argentea and others) | 70-75 °F (21-24 °C) |
| Cleome (Cleome hasslerana and others) | 70-75 °F (21-24 °C) |
| Coleus (Coleus scutellarioides) | 70-75 °F (21-24 °C) |
| Cosmos (Cosmos spp.) | 60-75 °F (15-24 °C) |
| Dahlia (Dahlia × hortensis) | 70-80 °F (21-27 °C) |
| Daisy, Dahlberg (Thymophylla tenuiloba) | 65-70 °F (18-21 °C) |
| Dusty Miller (Senecio cineraria) | 65-75 °F (18-24 °C) |
| Four-O’clock (Mirabilis jalapa) | 65-75 °F (18-24 °C) |
| Geranium or pelargonium (Pelargonium spp.) | 70-75 °F (21-24 °C) |
| Gourd, Ornamental (Cucurbita pepo and Lagenaria siceraria) | 70-95 °F (21-35 °C) |
| Impatiens (Impatiens walleriana) | 70-75 °F (21-24 °C) |
| Impatiens, New Guinea (Impatiens × hawkeri) | 70-75 °F (21-24 °C) |
| Lisianthus (Eustoma grandiflorum) | 70-75 °F (21-24 °C) |
| Lobelia, Bedding (Lobelia erinus) | 65-75 °F (18-24 °C) |
| Maple, Flowering (Abutilon spp.) | 70-75 °F (21-24 °C) |
| Marigold, African (Tagetes spp.) | 70-75 °F (21-24 °C) |
| Melampodium (Melampodium paludosum) | 65-70 °F (18-21 °C) |
| Moonflower (Ipomoea alba) | 85-95 °F (30-35 °C) |
| Morning Glory (Ipomoea spp.) | 70-85 °F (21-30 °C) |
| Nasturtium (Tropaeolum majus) | 65-70 °F (18-21 °C) |
| Pansy (Viola × wittrockiana) | 65-70 °F (18-21 °C) |
| Periwinkle, Madagascar (Catharanthus roseus) | 70-75 °F (21-24 °C) |
| Petunia (Petunia x atkinsoniana) | 70-80 °F (21-27 °C) |
| Pink, China (Dianthus chinensis) | 60-68 °F (15-20 °C) |
| Polka Dot Plant (Hypoestes phyllostachys) | 70-75 °F (21-24 °C) |
| Portulaca or Moss Rose (Portulaca grandiflora) | 75-85 °F (24-30 °C) |
| Sage, Mealycup (Salvia farinacea) | 70-75 °F (21-24 °C) |
| Sage, Scarlet (Salvia splendens) | 70-75 °F (21-24 °C) |
| Snapdragon (Antirrhinum majus) | 60-70 °F (15-21 °C) |
| Statice, Annual (Limonium sinuatum) | 68-75 °F (20-24 °C) |
| Stock, Brompton (Matthiola incana) | 60-65 °F (15-18 °C) |
| Strawflower, everlasting (Xerochrysum bracteatum, syn. Helichrysum bracteatum) | 70-75 °F (21-24 °C) |
| Sunflower (Helianthus annuus) | 70-85 °F (21-30 °C) |
| Sweet William (Dianthus barbatus) | 60-68 °F (15-20 °C) |
| Tobacco, Flowering (Nicotiana alata) | 70-75 °F (21-24 °C) |
| Verbena, Hybrid (Verbena × hybrida) | 70-75 °F (21-24 °C) |
| Wishbone Flower (Torenia fournieri) | 70-75 °F (21-24 °C) |
| Zinnia (Zinnia elegans) | 70-80 °F (21-27 °C) |
| Zinnia, Creeping (Sanvitalia procumbens) | 70 °F (21 °C) |
Thanks for this; There are plenty of charts for vegetable optimum germination temperatures but little for flower seeds. I have struggled with germinating begonia seeds for example despite having a temp controlled propagator.
Rgds,
Mike
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