This chart lists the optimum soil temperatures for starting flower and herb seeds. We’re often told seeds need warmth to sprout but you can overdo it. Find out what your seeds need to achieve the best germination rates.
Growing vegetables? This lists the recommended soil temperatures for starting vegetable seeds.
Why Soil Temperature Matters
No matter what type of flower or herb you are starting from seed, the basic needs are the same.
Water, air, and warmth.
When a seed is introduced to these things in the right way, the embryo inside the seed breaks dormancy and starts to grow.
The warmth part, or, more specifically, the temperature of the soil (potting mix, seedling mix) when germinating the seeds, can make a big difference.
Too low and the seed may not grow or will grow much slower than anticipated.
Too warm and the seed may sprout but die off.
In the sweet spot—the recommended soil temperature range—along with adequate water and air, the seed grows into a seedling as quickly and efficiently as possible.
The twist in all of this is each plant species has its own preferred soil temperature range.
As you’ll see from the chart below, some seeds need cooler conditions than others.
While it is completely unrealistic to cater to all of these different needs, you can give your seed- starting a boost by grouping seeds with similar needs together.
And, if you have ever struggled with any one particular type of seed, maybe that’s the one that does get special treatment.
Starting indoors, this could mean using a seed starting heat mat with a thermostat, ensuring that the potting mix stays in the best temperature range for the duration of germination.
You can use a standard digital kitchen thermometer to check soil temperatures. There are more tips here for how and when to use a heat mat.
Then, with your seeds sprouted, lower the temperature by about 5-degrees. Seeds need warmer temperatures to sprout than they do to grow.
Recommended Tool
I use a simple kitchen thermometer with a probe to check soil temperatures.
Digital thermometer with probe | Amazon
To know it’s time to sow outdoors, take several soil temperature readings per day over the period of several days. Place the probe about 3-inches deep. When your readings are averaging within the desired range, it’s sow time.
Flower & Herb Soil Temperature Sowing Chart
This chart lists recommended soil temperatures only. Check your seed packet for any recommended pre-treatments like scarification, stratification, or pre-soaking prior to sowing.
Before adding any plants to your garden, be sure they are non-invasive and suited to your growing region.
I’ve done my best to find reliable sources for this information using available studies and tips from growers. It’s not the same as testing in our own growing conditions but it’s the best we have.
See the Resources section to save this information to your device.
| Plants | Soil Temperature | Days to Germinate |
|---|---|---|
| Agastache (Agastache foeniculum, A. Anethiodora) | 55°F (12°C) | 14-21 |
| Sweet Alyssum (Lobularia maritima) | 55-70°F (13-21°C) | 8-10 |
| Amaranthus (Amaranthus spp.) | 65-75°F (18-24°C) | 7-10 |
| Aster & Symphyotricum (various) | 60-70°F (15-21°C) | 10-14 |
| Aurinia (Aurinia saxatilis) | 50-55°F (10-12°C) | 5-14 |
| Basil (Ocimum basilicum) | 68-70°F (20-21°C) | 7-10 |
| Bee Balm (Monarda spp.) | 60-70°F (15-21°C) | 14-30 |
| Bellflower (Campanula) | 70-75°F (21-23°C) | 14-21 |
| Black-Eyed Susan (Rudbeckia spp.) | 68-72°F (20-22°C) | 5-21 |
| Borage (Borago officinalis) | 65-85°F (18-29°C) | 7-14 |
| Butterfly Flowers (Tithonia rotundifolia) | 70°F (21°C) | 7-14 |
| Calendula (Calendula officinalis) | 70°F (21°C) | 7-21 |
| Chive (Allium schoenoprasum, Allium tuberosum) | 68-75°F (20-25°C) | 10-21 |
| Chervil (Anthriscus cerefolium) | 60-70°F (15-21°C) | 14-28 |
| Chamomile (Chamaemelum nobile, Matricaria recutita) | 70°F (21°C) | 14-21 |
| Cilantro | Coriander (Coriandrum sativuvm) | 55-68°F (13-20°C) | 14-21 |
| Cleome (Cleome hassleriana) | 70-80°F (21-27°C) | 7-14 |
| Columbine (Aquilegia spp.) | 65-75°F (18-25°C) | 21-28 |
| Coneflower (Echinacea spp.) | 65-70°F (18-21°C) | 20-30 |
| Coreopsis (Coreopsis lanceolata) Calliopsis, Tickseed | 55-70°F (12-21°C) | 5-25 |
| Cornflower / Bachelor’s Button (Centaurea cyanus) | 60-70°F (15-21°C) | 7-14 |
| Cosmos (Cosmos bipinnatus and C. sulfureus) | 70-75°F (21-25°C) | 7-10 |
| Cynoglossum (Cynoglossum amabile) | 65-75°F (18-25°C) | 5-10 |
| Dahlia (Dahlia spp.) | 70-75°F (21-25°C) | 14-20 |
| Daisy (Leucanthemum spp.) | 65-75°F (18-25°C) | 14-21 |
| Delphinium (Delphinium spp.) | 60-68°F (15-20°C) | 14-21 |
| Dianthus (Dianthus spp.) | 60-70°F (16-21°C) | 14-21 |
| Digitalis (Digitalis spp.) Foxglove | 60-65°F (15-18°C) | 14-21 |
| Dill (Anethum graveolens) | 60-70°F (16-21°C) | 7-21 |
| Eriophyllum (Eriophyllum lanatum) Common Wooly Sunflowers | 50°F (10°C) | 15-30 |
| Eryngium (Eryngium foetidum) Culantro, Shado beni, Mexican coriander | 80°F (26°C) | 14-28 |
| California Poppy (Eschscholzia californica) | 55°F (12°C) | 14-21 |
| Fennel (foeniculum vulgare) | 50-75°F (10-24°C) | 7-14 |
| Blanket Flower (Gaillardia spp.) | 70-75°F (21-25°C) | 14-21 |
| Flax (Linum usitatissimum) | 50-80°F (10-27°C) | 21 |
| Gaura (Gaura lindheimeri) | 65-75°F (18-25°C) | 14-30 |
| Geranium (Pelargonium) | 70-75°F (21-25°C) | 7-14 |
| Gypsophilia (Gypsophilia elegans) Baby’s Breath | direct sow before last frost in spring | 10-20 |
| Helenium (Helenium autumnale) | 70°F (21°C) | 7-10 |
| Hollyhock (Alcea rosea) | 60-70°F (15-21°C) | 10-14 |
| Iberis (Iberis umbellata) | 70-85°F (21-30°C) | 10-20 |
| Morning Glory (Ipomoea purpurea) | 70-85°F (21-30°C) | 5-21 |
| Lavender (Lavandula spp.) | 70-80°F (21-27°C) | 14-21 |
| Lavatera (Lavatera trimestris) Mallow, Annual Tree Mallow | 70°F (21°C) | 15-20 |
| Lemon Balm (Melissa officinalis) | 68-70°F (20-21°C) | 10-14 |
| Lemongrass (Cymbopogon citratus) | 70-85°F (21-29°C) | 5-21 |
| Lobelia (Lobelia erinus) | 65-75°F (18-25°C) | 15-21 |
| Lupin (Lupinus polyphyllus) | 55-65°F (12-18°C) | 14-60 |
| Marigold (Tagetes sp.) | 70-75°F (21-25°C) | 4-12 |
| Milkweed (Asclepias spp.) | 70-75°F (21-25°C) | 14-21 |
| Moonflower, Morning Glory (Ipomoea spp.) | 70-75°F (21-25°C) | 21-28 |
| Nasturtium (Tropaeolum majus) | 55-65°F (12-18°C) | 7-10 |
| Nepeta Catmint (Nepeta subsessilis) | 70-80°F (21-27°C) | 10-20 |
| Nigella (Nigella damascene) Love in a Mist | 65-70°F (18-21°C) | 10-15 |
| Oenothera (Oenothera pallida) | 65-70°F (18-21°C) | 5-30 |
| Oregano, Majoram (Origanum vulgare, Origanum marorana) | 68-70°F (20-21°C) | 14-21 |
| Parsley (Petroselinum crispum) | 50-75°F (10-24°C) | 14-30 |
| Phacelia (Phacelia tanacetifolia) | 68°F (20°C) | 15-30 |
| Phlox (Phlox drummondii) | 60°-65°F (16°-18°C) | 5-10 |
| Poppy (Papaver spp.) | P:68-70°F(20-21°C) A:60°F(16°C) | 14-28 |
| Ratibida (Ratibida pinnata) Yellow Coneflower | 68-75°F(20-25°C) | 7-42 |
| Roselle (Hibiscus sabdariffa) | 75-85°F (24-29°C) | 7-14 |
| Rosemary (Salvia rosmarinus, formerly Rosmarinus officinalis) | 80°-90°F (27°-32°C) | 14-21 |
| Black-Eyed Susan (Rudbeckia spp.) | 70-75°F (21-25°C) | 5-21 |
| Sage, Salvia (Salvia officinalis, S. elegans) | 75-78°F (24-26°C) | 7-21 |
| Saponaria (Saponaria ocymoides) Rock Soapwort | 70°F (21°C) | 10-21 |
| Savory (Satureja hortensis, Satureja montana) | 65-70°F (18-21°C) | 10-15 |
| Scabiosa (Scabiosa atropurpurea) Pincushion flower | 70-75°F (21-25°C) | 10-21 |
| Snapdragon (Antirrhinum majus) | 65-70°F (18-21°C) | 8-14 |
| St. John’s Wort (Hypericum perforatum) | 60-75°F (16-25°C) | 10-14 |
| Strawflower (Xerochrysum bracteatum) | 65-70°F (18-21°C) | 5-20 |
| Stevia (Stevia rebaudiana) | 68-75°F (20-25°C) | 7-21 |
| Sunflower (Helianthus spp.) | 70-75°F (21-25°C) | 14 |
| Sweet Pea (Lathyrus odoratus) | 55-65°F (12-18°C) | 28 |
| Thyme (Thymus vulgaris) | 60-70°F (16-21°C) | 14-21 |
| Mexican Sunflower (Tithonia rotundifolia) | 70-75°F (21-25°C) | 5-14 |
| Veronica (Veronica spicata) Speedwell | 65°F (18°C) | 14-21 |
| Yarrow (Achillea millefoliu) | 65-75°F (18-25°C) | 10-14 |
| Zinnia (Zinnia elegans) | 80-85°F (27-29°C) | 5-24 days |
Frequently Asked Questions
The ideal soil temperature for flower seed germination varies greatly depending on the species and variety. Sunflowers, for example, like a soil temperature from 70-75°F (21-25°C) while sweet peas prefer 55-65°F (12-18°C). Soil temperatures between 65°F-70°F (18-21°C) tend to suit many types of flower seeds.
Most flower seeds can germinate at room temperature around 70°F (21°C) if other conditions including moisture levels are suitable.
The best soil temperature for germinating herb seeds varies by species and variety but in general a temperature around 70°F (21°C) is suitable.
Not all flower seeds benefit from heat for germination. The best temperature for sprouting seeds depends on the species and variety. Check your seed packet for specific sowing instructions including whether added heat is recommended.
Heating mats can be used indoors to increase the temperature of potting mix or seed starting mix. Be sure to get one with a thermostat to avoid overheating. To increase outdoor soil temperatures when the planting time is right, cover the planting area with plastic mulch over several sunny days.
Resources
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Best Soil Temperatures For Sowing Flowers & Herbs
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Vegetables
This has a soil temperature chart for sowing vegetable seeds.
Like flower and herb seeds, these plants also have preferred soil temperature ranges for germination.
Sowing Tips
For an indoor seed starting plan, see 30 Flower Seeds To Start Indoors.
This has more on direct sowing outdoors before last frost.
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