Use this guide to start your seeds indoors at the right time and with the right temperatures to get them off to a strong start.
Starting your seeds indoors at the right time and in the right temperature range ensures that the plants get off to a good start. Planted too early or too late, seeds can rot and young plants may struggle to get established. The charts below provide the temperatures and timing you need to know to start seed for 24 common flowers and vegetables. Though germination temperature needs vary, once they’ve sprouted, most seedlings do just fine in a room that’s 60 to 70 degrees F.
Seed-starting jargon
Before getting started here's a quick guide to some of the technical terms used in the chart.
Stratification
Seeds that need a period of cold and moisture to break down a heavy seed coat in order to germinate. Gardener's can mimic this natural process by placing seeds in a container of moist sand or vermiculite and storing it in the refrigerator at 41 degrees F for at least 4 weeks. Perennials seeds often need stratification.
Scarification
Tough seed coats of sweet peas, nasturtiums and others need to nicked, cracked or softened so water can penetrate and encourage the seed to grow. Use a file or sandpaper to make a shallow nick or cut in the coating. You can also soak the seeds in water overnight but no longer or they may rot.
Needs light to germinate
Light is an important element that helps some seeds germinate. There's no need to make a hole when you're planting seeds like this. Just sprinkle them on the surface of the seed starting mix or soil.
Seedlings that can go outside early
These young plants thrive in cooler weather and can go outdoors in spring when it's 40 to 50 degrees F during the day.
| Plant name Botanical name | Germination temperatures | Days to germination | Weeks to planting outdoors | Comments |
|---|---|---|---|---|
|
Broccoli Brassica oleracea italica |
70 to 75°F | 7 to 10 | 5 to 7 | Set outside up to 2 weeks before last frost |
|
Cabbage Brassica oleracea capitata |
70 to 75°F | 5 to 10 | 5 to 7 | Can take a light frost |
|
Cauliflower Brassica oleracea botrytis |
75 to 80°F | 5 to 10 | 5 to 7 | Prefers cool temps or won’t produce head |
|
Pansy Viola x wittrockiana |
65 to 75°F | 7 to 15 | 8 to 12 | Benefits from stratification; can take frost; foliage freezes at 10°F |
|
Sweet pea Lathyrus odorata |
55 to 65°F | 14 to 21 | 4 to 6 | Benefits from scarification; can also be direct-sown outdoors; can take a light frost |
Seedlings that can go out after average last frost date
When temperatures are starting to warm up and the last average frost date for your area has gone by you can put these young plants out in the garden.
| Plant name Botanical name | Germination temperatures | Days to germination | Weeks to planting outdoors | Comments |
|---|---|---|---|---|
|
Artichoke Cynara scolymus |
70 to 80°F | 18 to 21 | 6 to 8 | Benefits from stratification; takes 5 to 7 months from sowing to crop |
|
Bells of Ireland Moluccella laevis |
65 to 68°F | 12 to 21 | 6 to 8 | Needs light to germinate; benefits from stratification; doesn’t like roots disturbed — use peat pots |
|
Butterfly weed Asclepias tuberosa |
70 to 75°F | 21 to 28 | 6 to 8 | Doesn’t like roots disturbed — use peat pots |
|
Celery Apium graveolens |
70 to 75°F | 20 to 25 | 10 to 12 | Seedlings need constant moisture to develop |
|
Foxglove Digitalis purpurea |
65 to 70°F | 15 to 20 | 10 to 12 | Needs light to germinate; biennial so may not bloom first year |
|
Hyacinth bean Lablab purpureus |
65 to 70°F | 5 to 12 | 6 to 8 | Benefits from stratification; can take up to 80 days to get beans |
|
Sage Salvia officinalis |
60 to 70°F | 7 to 21 | 6 to 8 | Needs light to germinate; let dry out between watering to avoid rot |
|
Statice Limonium sinuatum |
68 to 75°F | 12 to 20 | 8 to 10 | Needs light to germinate; plant seedlings outdoors 12 in. apart |
|
Sweet alyssum Lobularia maritima |
65 to 70°F | 8 to 10 | 4 to 5 | Plant seedlings outdoors 6 to 8 in. apart |
Seedlings you should wait to put outside until danger of frost has past
These warm-weather lovers are the last seedlings to go outdoors. They do best after all danger of frost has gone by and soil temperatures have warmed — usually when daytime temperatures are around 70 degrees F and the nights are in the 50s.
| Plant name Botanical name | Germination temperatures | Days to germination | Weeks to planting outdoors | Comments |
|---|---|---|---|---|
|
Celosia Celosia spp. and hybrids |
70 to 80°F | 8 to 14 | 4 to 6 | Pinch tip when 8 to 12 in. tall for branching |
|
Coleus Plectranthusspp. and hybrids |
70 to 75°F | 10 to 14 | 6 to 8 | Needs light to germinate; pinch tip when plants have four to six sets of leaves |
|
Cucumber Cucumis sativus |
68 to 72°F | 7 to 10 | 4 to 6 | Don’t disturb roots when transplanting |
|
Cup & saucer vine Cobaea scandens |
70 to 75°F | 10 to 30 | 6 to 8 | Benefits from scarification; vigorous grower, plant near a strong trellis |
|
Eggplant Solanum melongena |
80 to 90°F | 10 to 14 | 8 to 10 | Don’t set out too early, cool temps stunt growth |
|
Floss flower Ageratum houstonianum |
78 to 82°F | 5 to 10 | 6 to 8 | Needs light to germinate; plant seedlings outdoors 9 to 12 in. apart |
|
Joseph's coat Amaranthus tricolor |
70 to 75°F | 10 to 15 | 3 to 4 | Let dry out between watering to avoid rot |
|
Nasturtium Tropaeolum majus |
60 to 65°F | 7 to 14 | 4 to 6 | Benefits from scarification; can also be direct-sown outdoors; no need to fertilize after planting outside |
|
Pepper Capsicum annuum |
80 to 90°F | 7 to 10 | 6 to 8 | Don’t set out too early; cool temps stunt growth |
|
Tomato Solanum lycopersicum |
80 to 90°F | 7 to 14 | 5 to 6 | Plant leggy seedlings deep and they’ll form roots all along the stem for added support |
By Sherry Ribbey | October 17, 2019
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