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The short answer: plant basil outdoors when nighttime temperatures stay reliably above 50°F, usually 2 to 3 weeks after your last spring frost, and once soil has warmed to at least 60°F. Start seeds indoors about 6 weeks before that date for a head start. For most US gardeners the outdoor window runs from April in the South to early June in the North. Basil is one of the most cold-sensitive herbs you can grow — a single night in the 40s stunts it and cold below freezing kills it — so patience with timing pays off more than with almost any other crop.
Basil is fast, generous, and easy once it is warm, but it has zero tolerance for cold. Gardeners who rush it out with their hardy greens end up with blackened, stalled plants. Get the timing right and a few plants will supply pesto all summer. This guide gives the windows by zone, the temperatures that matter, and how succession sowing keeps tender leaves coming.
Why basil timing is all about warmth
Basil is a tropical annual, and it shows. Unlike lettuce, kale, or peas that shrug off a light frost, basil is damaged at temperatures well above freezing. Below 50°F, leaves develop dark cold spots, growth stalls, and the plant sulks; at 32°F, frost blackens and kills it in a single night. A cold snap early in the season can set a plant back for weeks even if it survives.
The practical rule: do not anchor basil to your last frost date alone — anchor it to a run of nights in the 50s or warmer. Waiting an extra week for genuine warmth produces a plant that grows away vigorously, while an early-planted one struggles and often gets passed by a later planting.
Planting windows by USDA zone
| USDA zone | Start seeds indoors | Plant outdoors |
|---|---|---|
| 3–4 | Mid to late April | Late May to early June |
| 5 | Early to mid-April | Mid to late May |
| 6 | Late March to early April | Mid-May |
| 7 | Mid-March | Late April to early May |
| 8 | Late February | April |
| 9–10 | January to February | March (grow through spring/fall) |
In hot zones 9 and warmer, basil grows through spring and fall but can struggle in the peak of summer heat, when it bolts (flowers) quickly; a little afternoon shade and steady water help. In cool zones, wait for settled warmth and consider growing basil in pots you can move indoors on cold nights.
Soil temperature matters too
Air temperature gets the attention, but soil temperature decides whether basil seeds germinate and transplants take off. Basil seed germinates best at 70°F soil and barely at all below 60°F, and transplants set into cold soil stall. Check soil with a thermometer 2 inches down mid-morning, and if your spring is cool, warm the bed under black plastic for a week or two before planting. In pots, this is easy — the mix warms fast in the sun.
Starting basil seeds indoors
Starting indoors about 6 weeks before your last frost gives you sturdy transplants ready to go the moment it warms — a real advantage in short seasons.
- Sow shallowly, about 1/4 inch deep, in a moist seed-starting mix; basil needs warmth (70°F+) and a little light to germinate.
- Give strong light immediately on sprouting — 14 to 16 hours under a grow light — or seedlings stretch tall and weak.
- Thin or pot up to give each plant room once true leaves appear.
- Harden off over about a week before transplanting, and only once nights are above 50°F.
For the full indoor routine see how to start seeds indoors, and if seedlings get tall and floppy, the leggy seedlings fix explains why. A good starting setup is compared in the best seed starting kit roundup.
Direct-sowing outdoors
Once frost is past and soil is 60 to 70°F, basil is easy to direct-sow. Scatter or space seeds 1/4 inch deep, keep the surface moist, and expect germination in 5 to 10 days in warm soil. Thin seedlings to 8 to 12 inches apart once they have a couple of true leaves. Direct-sowing skips transplant shock and, in warm ground, basil grows so fast it quickly catches up to indoor-started plants. See direct sow vs transplant for how to choose.
Succession sow for a full season
Basil is an annual that eventually bolts and turns bitter, so the trick to a continuous supply is succession sowing: start a small new batch every 3 to 4 weeks through early summer. As the first planting begins to flower and lose flavor, the next is coming into its prime. Regular pinching of the growing tips also delays bolting and keeps plants bushy and productive. See the succession planting schedule for how to stagger sowings across the garden.
Signs it is warm enough to plant
Rather than trusting the calendar alone, read these signals that conditions are genuinely basil-ready:
- Nights consistently above 50°F for a week or more, with no frost in the 10-day forecast. This is the single most important cue.
- Soil at 60°F or warmer at 2 inches deep, mid-morning — check with a soil thermometer.
- Tomatoes and peppers are already out and growing, since basil shares their warmth needs but is a touch more tender.
- Warm-season weeds like crabgrass and purslane are germinating, a natural indicator the soil has warmed.
If a late cold snap threatens after you plant, cover basil overnight with a cloche, bucket, or row cover, or move pots indoors — a single cold night can undo weeks of growth. When in doubt, wait a week; basil grows so fast in warm soil that a later start rarely costs you much and often outperforms a chilled early planting.
Timing basil grown in pots and indoors
Container growing gives you more freedom with timing. Because potting mix warms faster than garden soil and pots are portable, you can plant basil in a pot a week or two earlier than in the ground, moving it into a garage or indoors on cold nights. This is the safest way to get an early start in a cool spring.
Basil can also be grown indoors year-round on a sunny windowsill or under a grow light, sidestepping outdoor timing entirely — useful for a winter supply in cold zones. Indoor basil needs 6 or more hours of bright light (or 12 to 16 under a grow light), warmth above 50°F, and a well-draining pot. Sow a fresh indoor pot every couple of months for a continuous kitchen supply through the off-season.
Timing basil with tomatoes and peppers
Basil is a classic companion for tomatoes and peppers — in the kitchen and, many gardeners find, in the bed. It shares their warm-season timing almost exactly, but because basil is a touch more cold-sensitive, plant it at the same time as or just after those crops, never before. Interplanting basil among tomatoes saves space and the two enjoy identical sun and water. See when to plant tomatoes to line up the schedule.
Once basil is in and growing, the main ongoing job is watering it correctly — see how often to water basil and why is my basil turning yellow. Browse the full seeds and vegetable growing hub. Our product picks come from aggregated owner reviews and expert consensus, never first-hand testing — see how we rank.