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When to start seeds indoors

By: Sherri Ribbey
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.

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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
Plectranthus spp. 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

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Published: Oct. 17, 2019
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