In Alabama, indoor seed starting runs from early December to mid-March, depending on the crop. Onions and leeks go first, December 4 to December 26. Broccoli, cabbage and head lettuce follow January 1 to January 23, peppers and eggplant January 15 to January 30, and tomatoes February 5 to February 27. Those dates count back from a last spring frost of roughly March 19 to April 3, the range at Huntsville in north Alabama. Gardens on higher ground should sow later, and gardens farther south can sow earlier.
The date everything counts back from
Every indoor sowing date is a countdown. A seedling needs a set number of weeks in a pot before it can go outside, so the sowing date is the planting-out date minus those weeks. For the planting-out date, gardeners use the last spring frost. NOAA’s 1991-2020 Climate Normals put the last spring freeze (32°F) at Huntsville International Airport, in north Alabama, at roughly March 19 to April 3, depending on the probability level you choose. Stations farther south see it earlier.
That is a range, and the two-week spread matters. Sow to the early end of a crop’s window when your garden is colder and your frost comes late, and the seedlings reach transplant size while frost is still possible. They wait in their pots, outgrow the cells and stretch toward the light, and by the time they go out they are tall, floppy and root-bound. Sow to the late end when your frost really came in mid-March, and you lose weeks. The plants reach the bed small, and the head start you were chasing is gone.
The Huntsville reading is the reference point, and your yard probably differs. Suburban and rural gardens can see the last spring frost later than an airport does, especially in low-lying cold pockets and at elevation. Higher ground has a later last frost, so every sowing date shifts later there. Gardens farther south, toward the Gulf Coast, have an earlier last frost and shift earlier. Your county extension office can tell you which end of the range fits your ground, and the page on first and last frost dates in Alabama shows how the dates move across the state.
Hardiness zones will not settle this. The USDA Plant Hardiness Zone Map 2023, built on 1991-2020 normals, places Alabama in roughly zones 7 to 9. That system rests on one variable, the average annual extreme minimum temperature, so it tells you which perennials survive winter. Two gardens in the same zone can still have last frosts that differ by weeks.
For seed starting, the decision to write on the calendar is this: count back from both ends of March 19 to April 3, then pick the end that matches your own frost.
The calendar, crop by crop
The weeks below come from University of Minnesota Extension’s table of how long to keep seeds indoors before planting out. They are the usual guidance among extension services and not a law, and the dates are calculated for Alabama’s frost range. Minnesota’s own calendar months do not apply here.
| Crop | Weeks indoors before planting out (usual guidance) | Sow indoors in Alabama |
|---|---|---|
| Leeks, onions | 14-15 weeks | December 4 to December 26 |
| Celery | 12-13 weeks | December 18 to January 9 |
| Broccoli, Brussels sprouts, cabbage, cauliflower, head lettuce | 10-11 weeks | January 1 to January 23 |
| Eggplant, okra, peppers | 9 weeks | January 15 to January 30 |
| Tomatoes | 5-6 weeks | February 5 to February 27 |
| Sweet potatoes (slips) | 3-4 weeks | February 19 to March 13 |
Read the table from the top and the pattern is clear: the slowest crops go first. Onions and leeks start as thin, grassy seedlings that need the longest runway, which is why they are sown in December while the garden is bare. Celery follows. The cabbage family (broccoli, cabbage, cauliflower, Brussels sprouts) and head lettuce come next, in January, since they like to be planted out while the weather is still cool. The table counts every crop back from the same frost date for simplicity, but these hardy crops can go out earlier than the tender ones. For head lettuce in particular, the page on starting lettuce covers sowing depth and timing.
Peppers, eggplant and okra come later because they hate cold. They are also slow to germinate and slow to size up, so nine weeks is a sensible allowance. Sow them January 15 to January 30. Tomatoes need much less time, and that surprises people who sow them in January and end up with overgrown, spindly plants by March. A tomato tray started February 5 to February 27 is plenty. The growing tomato seedlings indoors page goes deeper on potting up and pacing.
Sweet potatoes are the odd one out. They are grown from slips, the leafy sprouts that grow from a mature root, and three to four weeks is enough to produce them. Slips go out late, once the soil is truly warm.
Tender crops (tomatoes, peppers, eggplant, okra, sweet potatoes) count back from the frost date, yet their real planting-out day is when cold nights are done and the soil has warmed. If your garden sits at the colder end, use the later sowing date and do not rush them outside.
Which crops should not be started indoors?
Anything with a taproot or a sensitive root system does better sown where it will grow. Carrots, beets, radishes and turnips fork, stunt or bolt when transplanted. Beans and peas are fast and sprout reliably in garden soil, so the weeks of work buy nothing. Squash, cucumbers and melons can be started indoors in a short window, but most gardeners get better results sowing them directly, because their roots resent disturbance and they grow fast once the soil is warm. Sweet corn goes in the ground too. If a crop is not in the table above, assume it belongs outdoors, and check the Alabama planting calendar for its direct-sowing window.
Light, warmth and hardening off
Seedlings kept on a windowsill often stretch. Winter days in Alabama are short, and even a bright south-facing window delivers light from one direction. The plant grows toward it, putting its energy into a long, pale stem instead of a thick, dark-green one. Leggy seedlings are weak, fall over after transplanting and take longer to catch up. A shop light or grow light hung just above the leaves fixes this. Keep it close, raise it as the plants grow, and run it on a timer for a long day. Gentle air movement from a small fan also thickens stems.
Warmth matters just as much at germination. Seeds sprout best when the soil holds a steady temperature, and an unheated porch or a drafty room that swings between warm days and cold nights slows everything down. Peppers and eggplant are among the pickiest. A heat mat made for seed trays, set under the cells, keeps them consistently warm. Take the mat away once most seeds have sprouted, since growing seedlings do better a bit cooler.
Cell trays dry out fast under lights, so check them daily. Water from below when you can, and keep the mix damp, not soggy. Once the first true leaves appear, thin to one seedling per cell by snipping the extras at the soil line instead of pulling them, which would tear the roots of the one you are keeping.
The last step before the garden is hardening off. Plants raised indoors have never felt direct sun, wind or a cool night, and moving them straight into the bed scorches leaves and sets them back. University of Minnesota Extension advises that all plants should be hardened off over the last 1 to 2 weeks before planting out. Start with an hour or two in shade, add more sun and more time each day, and finish with nights outdoors if the forecast is mild. Alabama’s spring sun is strong, so keep the first sessions in shade. Bring the trays in on any night that threatens frost.
What goes wrong
What happens when you start seeds too early?
The plants get ahead of the weather. Seedlings that are ready weeks before the garden is safe become tall and thin, circle their roots in the cell and sometimes flower while still tiny, which stunts the plant afterward. The fix is prevention: count back from your own last frost. If you are caught with plants that are ready too soon, pot them up into larger containers, keep them under light and give up the idea of rushing them outside. A pepper that waits two weeks in a bigger pot does better than one planted into a frost.
What is damping off, and how do you prevent it?
Damping off is a fungal disease. A seedling that looked fine yesterday has a thin, water-soaked stem at the soil line and falls over, usually in a whole patch of the tray. It follows wet, cool, stagnant conditions. Use a fresh, sterile seed-starting mix, clean the trays between uses, water only when the surface starts to dry, and keep air moving across the plants. Do not crowd seeds in the cell, and thin early.
What happens if you plant out the week after the average last frost?
The average date is a middle point, so frost after it is not impossible. March in Alabama can produce a run of warm days, and the temptation to move tomatoes and peppers outside is strong. A late frost blackens leaves in a night, and even without frost, cold soil stalls peppers, eggplant and okra for weeks. Gardens at the colder end of the state face this longest. Keep row cover or old bedsheets handy well past April 3, and longer in colder counties and on higher ground, and wait for the soil to warm before putting out the tender crops.
Common questions
When should I start tomato seeds indoors in Alabama?
February 5 to February 27 works for a garden whose last frost falls in the March 19 to April 3 range. Tomatoes need only 5 to 6 weeks indoors, so starting in January produces plants that are too big. In colder parts of the state, choose the later part of the window.
Can I start lettuce seeds indoors?
Head lettuce can, and University of Minnesota Extension gives 10 to 11 weeks indoors, which in Alabama means January 1 to January 23. Loose-leaf lettuce is easier sown directly in a cool bed, and the guide to starting lettuce covers both approaches.
Which vegetables should be sown straight into the garden?
Carrots, beets, radishes, turnips, beans, peas and sweet corn are direct-sown crops. Squash, cucumbers and melons are usually sown directly as well. The Alabama planting calendar lists their outdoor windows.
How do I adjust these dates for my own garden?
Find out when your last frost usually lands. Gardens on higher ground and in cold pockets have a later last frost, so every sowing date moves later. Those farther south move earlier. Your county extension office can give a local date, and more Alabama guides cover the rest of the growing year. The weeks indoors never change, so slide every row of the table by the same amount.
Sources: ncei.noaa.gov | extension.umn.edu