What Seeds to Plant Early in Spring (and What to Wait On)

Written by Kathy Keeler, A Wandering Botanist, for Park Seed

Seeds to Plant Early/ Seeds to Plant Late

Knowing which seeds to plant early in spring, and which ones to hold back, is the single decision that separates a strong start from a frustrating one. The split comes down to temperature: some seeds are built for cold soil, and some will stall or die in it. Once you know which camp a plant falls into, timing becomes straightforward (see the "July Rule" in the FAQs).

When to plant first and what to plant? Good weather in early spring gets us out into the garden, eager to get started. Of course you can prepare the ground, cleaning off dead stems. But then what?

Plant seeds.

But not all seeds, or the plants that grow from them, are the same. Some plants thrive at cool air and soil temperatures. Others cannot. The former are often called “cool season crops.” Their seeds can be planted “as soon as the soil can be worked,” which is to say, when it has thoroughly thawed. Cool season vegetables include peas, lettuce and radishes (detailed list below). These are plants from chilly climates that shrug a light frost and wilt in hot dry summers.

Cool Season Seeds: What Frost Won't Stop

Although they thrive in the cooler temperatures of spring (and fall) it is possible to plant cool season plants too early. If the seedlings are just coming up and you get a severe winter storm, burying them in snow and then cold snowmelt for a week or more, the little plants may not survive. In that case you will have to plant new seeds. If you shrug and say, “rats, bad luck, storms happen,” then get ahead and plant early. If you are annoyed— “all that work wasted!”—then wait two weeks or more until it is warmer to plant. “Four to six” or “two to three” weeks before the last frost date is the usual advice on the seed packets. That’s true, but years vary, sometimes a lot, so you’ll still have to decide. Do get the seeds in six weeks or more before your climate turns summer-hot though, because most cool season plants do not grow well when it is over 80^oF.

Cool Season Vegetables You Can Plant Before Last Frost

Artichoke, arugula, asparagus, beets, bok choi, broccoli, Brussels sprouts, cabbage, carrots, cauliflower, celery, chard (Swiss chard), chickpeas (garbanzo beans), Chinese cabbage, chives, collard greens, fennel, garlic, kohlrabi, leeks, lettuce, mustards (for green or for seeds), onions, parsnips, peas, radishes, spinach, turnips, and wasabi are common cool season vegetables.

Crop	Min Soil °F	Opt Range °F	Days to Maturity
Artichoke	50	65–85	85–100 (from transplant)
Arugula	40	45–65	30–40
Asparagus	50	75–85	2–3 years (from seed)
Beets	40	65–85	50–70
Pak Choi	40	60–75	45–60
Broccoli	40	60–85	60–90
Brussels Sprouts	40	60–85	80–100
Cabbage	40	60–85	70–120
Carrots	40	65–85	70–80
Cauliflower	40	65–85	55–100
Celery	40	60–70*	100–120
Chard (Swiss)	40	65–85	50–60
Chickpeas	40	65–85	90–100
Chinese Cabbage	40	60–75	50–80
Chives	40	60–75	60–90
Collard Greens	40	60–85	60–80
Fennel	40	60–75	65–90
Garlic	32	65–85	90–150
Kohlrabi	40	60–85	45–60
Leeks	32	65–85	100–120
Lettuce	32	60–75	45–75
Mustard Greens	40	60–75	30–40
Onions	32	65–85	100–120
Parsnips	32	65–75	100–120
Peas	40	65–75	60–70
Radishes	40	65–85	22–30
Spinach	32	65–75	40–50
Turnips	40	60–95	45–60
Wasabi	45	50–65	18–24 months
* Celery needs 10–15°F temperature drop at night for good germination; optimal is 85°F day / 70°F night.  Soil temperature data sourced from UC Cooperative Extension GN154 (Harrington, UC Davis). Days to maturity are representative ranges; specific variety performance will vary.

Cool Season Flowers to Direct Sow in Early Spring

Buttercups, calendulas (but not marigolds (Tagetes)),  columbine, johnny-jump-ups, pansies, poppies, snapdragons, sweet alyssum, sweet peas, violets, (Viola species) are cool season flowers. Plant them early.

Flower	Min Soil °F	Opt Germ Range °F	Seed to First Bloom
Buttercups (Ranunculus)	40	50–65	90–120 days
Calendula	40	55–70	45–60 days
Columbine	32	65–70	90–120 days*
Johnny-Jump-Ups (Viola)	35	65–70	60–80 days
Pansies	35	65–75	70–90 days
Poppies	32	50–65	60–90 days
Snapdragons	40	65–75	90–120 days
Sweet Alyssum	40	55–70	45–60 days
Sweet Peas	40	50–65	60–90 days
Violets (Viola spp.)	35	65–70	60–80 days
* Columbine performs best direct-sown in fall or early spring; cold stratification improves germination. Seed-to-bloom times assume direct sowing at the start of cool season. Starting indoors 8–10 weeks earlier is recommended for snapdragons and pansies.

Warm Season Seeds: Wait Until the Soil Is Ready

Seeds not to plant early include all the “warm season plants.” These are seriously stunted or killed by freezing temperatures, so should be planted “when all chance of frost has passed” and the soil is quite warm. (If you aren’t willing to sit on the ground while weeding because the ground is too cold, it’s too cold for warm season seeds.) Many warm season garden plants are from tropical regions and are killed by even light frosts. Frost kills because water expands when it freezes, tearing up cells. Plants from places that freeze frequently have defenses against the damage from expanding water. Other warm season plants, though, grow fine in regions with cold winters, but they avoid the frost; their seeds sprout after the last frost and the plants have gone to seed or died back to the roots by the first fall cold snap. Lots of important garden plants are warm season, from tomatoes to pumpkins to marigolds and dahlias.

Warm season plants include the plants that flower and fruit abundantly in hot, hot weather.

Warm Season Vegetables That Need Frost-Free Soil

Beans, cantaloupe, chilis, corn, dill, eggplant, endive, gourds, okra, parsley, peppers, pumpkins, soy beans, squash, tomatoes, watermelon, and zucchini are the most popular warm season plants.

Crop	Min Soil °F	Opt Range °F	Days to Maturity
Beans (snap / bush)	60	75–85	50–60 days
Cantaloupe	60	75–85	70–90 days
Chilis / Hot Peppers	60	65–75	70–100 days
Corn (sweet)	50	65–95	60–90 days
Dill †	40	60–70	40–60 days to harvest
Eggplant	60	75–85	70–85 days
Endive / Escarole †	40	60–75	85–100 days
Gourds	60	85–95	90–120 days
Okra	60	85–95	50–65 days
Parsley	40	65–85	70–90 days to harvest
Peppers (sweet)	60	65–75	65–80 days
Pumpkins	60	85–95	90–120 days
Soybeans / Edamame	60	75–85	75–95 days
Squash (summer)	60	85–95	45–60 days
Squash (winter)	60	85–95	80–110 days
Tomatoes	50	65–85	60–90 days
Watermelon	60	75–95	70–90 days
Zucchini	60	85–95	45–55 days
Soil temperature minimums sourced from UC Cooperative Extension GN154 (Harrington, UC Davis). Days to maturity are representative ranges across common varieties; specific performance varies by cultivar and climate. † Dill germinates in cooler soil but is listed here as she placed it in the warm season list — harvest timing is warmth-dependent. † Endive straddles seasons; it handles light frost but bolts in heat, making it best timed as a warm-start/cool-finish crop.

Warm Season Flowers: Plant After Last Frost, Not Before

African daisy, amaranths, asters, bachelor buttons, black-eyed Susans, cleome, coleus, coreopsis, cosmos, dahlias, Echinacea, four O’clocks, impatiens, lobelias, marigolds, petunias, strawflowers, sunflowers, and zinnias are all warm season garden flowers.

Flower	Min Soil °F	Opt Germ Range °F	Seed to First Bloom
African Daisy (Osteospermum)	50	60–70	60–80 days
Amaranth	60	70–80	50–75 days
Asters (China aster)	60	65–75	90–120 days
Bachelor Buttons (Cornflower) †	40	60–70	60–90 days
Black-Eyed Susan (Rudbeckia)	60	70–75	60–90 days
Cleome (Spider Flower)	60	70–80	60–75 days
Coleus	65	70–85	60–90 days
Coreopsis	60	65–75	60–90 days
Cosmos	60	65–75	50–70 days
Dahlias	60	70–80	90–120 days
Echinacea (Coneflower) †	60	65–75	120–180 days*
Four O'Clocks	60	68–86	60–75 days
Impatiens	65	70–80	70–90 days
Lobelia †	55	65–75	70–90 days
Marigolds	60	70–75	45–75 days
Petunias	60	65–75	70–90 days
Strawflowers (Helichrysum)	60	68–75	55–70 days
Sunflowers	60	70–85	60–90 days
Zinnias	60	70–75	45–70 days
Seed-to-bloom times assume direct sowing after last frost at optimal soil temperature. Starting indoors 6–8 weeks earlier is recommended for asters, coleus, dahlias, echinacea, impatiens, and petunias to ensure a full bloom window. † Bachelor buttons are technically cool-tolerant (will germinate in 40°F soil) and can be sown before last frost; they are listed here as she placed them in the warm season list. † Lobelia tolerates cooler soils than most warm-season flowers and benefits from indoor starting 10–12 weeks before last frost. * Echinacea from seed often blooms in its second year; some varieties bloom the first year with early indoor starting.

 

This post is “Seeds to Plant Early” so the list of warm season plants is not intended as covering all plants, but is a heads up about those that can’t take cold.

There are other methods beyond planting seeds into the soil. You can get bigger plants with more flowers sooner if you germinate the seeds indoors and transplant small plants outdoors (carefully, since outdoors is cooler and more variable than indoors.) However, tap-rooted plants often transplant poorly, so read about transplanting the particular plant before starting lots of its seeds indoors. Plants like tulips and calla lilies are usually propagated from bulbs or rhizomes, so are not covered here.

As winter ends, stock up on cool season seeds, prepare the ground and “as soon as the ground can be worked” PLANT!

Frequently Asked Questions

How do I know if a seed is cool season or warm season?

Use the July Rule. Ask what the plant does in July. In general, cool season plants fade, bolt, or go bitter when summer heat arrives. Warm season plants hit their stride. If a plant peaks in August, it needs warm soil to get started. If it's already struggling by August, its seeds can go in while the ground is still cold.

What seeds can I plant in early spring before the last frost?

Peas, spinach, lettuce, radishes, and kale can all go in before the last frost, they're built for cold soil and will shrug off a light freeze. Most gardeners plant these four to six weeks before their average last frost date, as soon as the ground has thawed enough to work. Arugula, bak choi, and chard are also reliable early starters.

How do I know if my soil is warm enough to plant seeds?

A simple test: kneel down and press your palm flat on the bare soil for ten seconds. If it feels uncomfortably cold, the kind of cold you'd complain about if you were weeding, it's too cold for warm season seeds. Cool season seeds tolerate that. Tomatoes, beans, and squash need soil that actually feels mild, not just thawed.

Why do warm season seeds fail when planted too early?

Frost kills by freezing the water inside plant cells. When water freezes, it expands and tears the cell walls. Plants from tropical regions never evolved a defense against this, so even a light frost that a pea shrugs off can kill a bean seedling overnight. Cold soil also prevents germination: warm season seeds like corn, squash, and tomatoes will simply sit dormant rather than sprout.

Can you plant cool season vegetables too early?

Yes. A severe late-winter storm with heavy snow followed by days of cold snowmelt can kill seedlings that were just emerging. Whether that risk is acceptable depends on your temperament. If replanting is just annoying, plant early. If it feels like a real loss, wait two or three more weeks. The plants don't care which you choose; the risk is yours to weigh.

What's the difference between cool season and warm season flowers?

Cool season flowers like pansies, sweet peas, poppies, and  snapdragons, handle frost and fade in summer heat. Warm season flowers like zinnias, sunflowers, marigolds, and cosmos, germinate in warm soil and bloom hard through heat and humidity. Plant the cool ones early. Plant the warm ones after your last frost date, when the soil has lost its chill.

Should I start seeds indoors or direct sow in the ground?

It depends on the plant. Starting indoors gives you a head start and lets you get big plants into the ground with blooms or fruit sooner. But tap-rooted plants like carrots, beets, poppies, and most beans, transplant poorly. Direct sowing is simpler and works well for nearly all cool season crops. Check the specific plant before you commit to starting a flat of something that would have done better in the ground.