Gardening

Temperature Chart for Germinating Annuals

20180308A growingfamily.co.uk.jpg
There is an ideal temperature for each type of seed. Source: growingfamily.co.uk

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)

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

2 comments on “Temperature Chart for Germinating Annuals

  1. 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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