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Best Soil Temperatures For Sowing Flower & Herb Seeds

Published on September 27, 2021 ♛ By Melissa J. Will

This post contains affiliate links.
Read full disclosure statement here.

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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 temperatures for starting vegetable seeds.

Flowers from seeds started at optimum germination temperatures.

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.

Seedling heat mat with thermometer.

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 also 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.

Flower & Herb Seed Starting Temperature 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 but different varieties may have slightly different preferences. Just do what you can to be as close to mid-range as possible and the seeds will do the rest.

Recommended Tool

I use a simple kitchen thermometer with a probe to check soil temperatures.

Digital meat thermometer.

Digital thermometer with probe | Amazon

PlantsSoil TemperatureDays 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 spring10-20
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

For an indoor seed starting plan, see 30 Flower Seeds To Start Indoors.

This has more on direct sowing outdoors before last frost.

I hope this helps improve your seed starting efforts. If you enjoy tips like this, be sure to sign up for the free Empress of Dirt Newsletter (every two weeks).

~Melissa the Empress of Dirt ♛

Seed Starting For Beginners ebook cover.

Seed Starting for Beginners
Sow Inside Grow Outside

by Melissa J. Will

NEW EDITION | Everything you need to get started with indoor seed starting for indoor and outdoor plants. Grow what you want—any time of year!

About This Ebook

This ebook is a digital file (PDF format) you save to your device. It is not a physical product.

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Flowers from seeds started at optimum germination temperatures.
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Melissa J. Will - Empress of DirtWelcome!
I’m Melissa J. Will a.k.a. the Empress of Dirt (Ontario, Canada).
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