Count back from the last spring frost. Around Atlanta, NOAA’s 1991-2020 Climate Normals put that frost between March 11 and March 29. Onions and leeks go in first, sown indoors November 26 to December 21. Peppers and eggplant follow from January 7 to January 25, and tomatoes come near the end, January 28 to February 22. Farther north the dates slide later, and nearer the coast they slide earlier. The full crop-by-crop table follows below.
The date everything counts back from
A seed packet gives a number of weeks, and the calendar gives a frost date. The sowing date is the second minus the first. University of Minnesota Extension publishes a widely used table of how many weeks each crop spends indoors before it goes out: 14-15 weeks for leeks and onions, 12-13 weeks for celery, 10-11 weeks for broccoli, cabbage and head lettuce, 9 weeks for peppers, eggplant and okra, and 5-6 weeks for tomatoes. Only those week counts travel south. The calendar months in that table belong to Minnesota and would put a Georgia gardener months off.
What is the last spring frost date in Georgia?
The reference point here is Atlanta, where NOAA’s NCEI 1991-2020 Climate Normals (station USW00013874) give a 32°F last spring freeze between March 11 and March 29. That range comes from the 30 to 70 percent probability band, so no single day is the frost date. In roughly seven years out of ten a freeze still arrives after the early end of the range, and in roughly three years out of ten it arrives after the late end. You can read the underlying data on the NOAA NCEI normals service.
Because the frost date is a range, every sowing date becomes a range too. Take tomatoes at 5-6 weeks indoors. Six weeks back from March 11 lands on January 28, and five weeks back from March 29 lands on February 22. Anywhere in between works. The ends of the window are where trouble lives.
Sow at the early end and the seedlings may spend extra weeks in their pots waiting for the weather to catch up. They stretch, the stems get thin and the roots circle the container. Sow at the late end and you lose weeks of growth. The plants reach the garden small, and cool-season crops like broccoli and cabbage meet warm weather before they have made a good head. Gardeners with a bright, warm growing setup can lean early. Those working from a cool windowsill will do better in the middle of the window.
Atlanta is a useful reference, but it sits on an urban airport and runs warmer than the countryside around it. North Georgia and the mountains have a later last frost, so every sowing date there moves later. The coastal plain runs milder, and its dates move earlier. The USDA Plant Hardiness Zone Map 2023 shows hardiness zones running from the cold north Georgia mountains to the mild coast, but that system rests on a single variable, the average annual extreme minimum temperature. It does not tell you when the last freeze falls. For your own yard, use the local frost range in First and Last Frost Dates in Georgia, ask your county extension office, and see the other Georgia guides for regional detail.
The calendar, crop by crop
This seed starting calendar uses the usual extension guidance on weeks indoors. Those weeks are general horticultural practice, not a law, and a strong grower with good lights can shave a bit off. The sowing windows are counted back from Atlanta’s March 11 to March 29 last-frost range.
| Crop | Weeks indoors before planting out | Sow indoors (Atlanta area) |
|---|---|---|
| Leeks, onions | 14-15 weeks | November 26 to December 21 |
| Celery | 12-13 weeks | December 10 to January 4 |
| Broccoli, Brussels sprouts, cabbage, cauliflower, head lettuce | 10-11 weeks | December 24 to January 18 |
| Eggplant, okra, peppers | 9 weeks | January 7 to January 25 |
| Tomatoes | 5-6 weeks | January 28 to February 22 |
| Sweet potatoes (slips) | 6-8 weeks | January 14 to February 15 |
The order of the table follows a simple logic. Slow, fine-seeded crops like onions and leeks need the longest head start, since the seedlings grow as thin as blades of grass. The cool-season brassicas come next, and head lettuce shares their window. The warm-season fruiting crops start later because they sit in pots for fewer weeks and grow quickly once warm. For peppers and eggplant, plan on January 7 to January 25, just before the tomato window opens.
One adjustment matters. The table counts to the last-frost range, but crops differ in how they handle the cold. Onions, broccoli and cabbage tolerate a light frost and can go outdoors somewhat ahead of that range. Tomatoes, peppers, eggplant, okra and sweet potatoes cannot, so they wait until freezing weather is past. A pepper sown at the early end of its window will be larger at planting-out than one sown at the late end. Our guide to Growing Tomato Seedlings Indoors covers the tomato side in more detail. For lettuce, Starting Lettuce also covers sowing it straight into the ground. Once the seedlings are ready, the Georgia Planting Calendar shows when each crop goes into the garden.
Which crops should not be started indoors?
Root crops are the clearest case. Carrots, beets, radishes, parsnips and turnips form a taproot or storage root that dislikes being disturbed, and a transplanted seedling often grows a forked or stunted root. Sow them where they will grow.
Beans germinate fast in warm soil and gain little from a pot. Seedlings kept indoors get root-bound before the garden is warm enough for them. Squash, pumpkins, cucumbers and melons are similar in most cases. They grow quickly, and their roots resent a move. A short head start in a pot helps only where the growing season runs out early, which is rarely a problem in a state with a long warm season. Sweet corn and peas also go straight into the ground.
Light, warmth and hardening off
A sunny window looks bright to us, but it is weak light for a seedling. January days are short, the sun sits low, and the light comes from one side. The seedlings lean toward it and stretch, making pale, thin stems that flop over. The fix is a light source mounted just above the leaves, such as a shop light with a fluorescent or LED tube. Raise it as the seedlings grow, and keep it close enough that the plants never reach for it. A window is fine for the first few days after sprouting, but it will not carry a seedling through the weeks listed in the table.
How warm should seed trays be kept?
Germination wants steady warmth more than peak warmth. Seeds in a cold room germinate slowly and unevenly, and the damp mix invites rot while they wait. Warm-season crops such as peppers, eggplant, okra and tomatoes are the slowest to sprout in a cool house, and a heat mat under the tray helps them. Cool-season crops like onions, broccoli and lettuce germinate happily in a cooler spot. Once most seeds have sprouted, take the tray off the mat. Seedlings need light more than heat at that point, and too much warmth encourages more stretch.
Hardening off is a step many people skip. Seedlings raised indoors have soft leaves that scorch in direct sun and wind. The usual extension guidance is to harden off all plants over the last 1-2 weeks before planting out. Start with an hour or two in shade, sheltered from wind, then lengthen the time each day and move toward full sun. Bring the plants inside on cold nights. For warm-season crops, hardening off begins while the last-frost range is still running, and the plants stay protected at night until freezing weather is past. After the last day or two of that process, they are ready to go in the ground.
What goes wrong
Three common problems can ruin a seed-starting season. The first is starting too early. The seedlings are tall, pale and floppy, the roots circle the bottom of the pot, and the plants slow down after transplanting. Count back from the frost range and hold off sowing until the window opens. If a crop has already gotten ahead of the weather, pot it up into a larger container and keep it under lights until the garden is ready.
What causes seedlings to collapse at the soil line?
Damping off. The stem pinches thin right at the soil, and the seedling falls over, often overnight. It is caused by soil-borne water molds and fungi that thrive in cold, soggy, crowded conditions. Prevent it with clean trays, fresh seed-starting mix (garden soil carries the organisms), light watering from the bottom, and a small fan for air movement. Thin crowded seedlings early. Once a tray shows the problem, remove the affected seedlings and let the surface dry.
The third problem is planting out too soon. A date in the middle of the frost range is an average, so a freeze after it is routine in some years. Soil that is still cold also slows root growth, so tender plants set out too early may be damaged by a late freeze or simply stop growing. Peppers, eggplant and okra are especially prone to suffer. Watch the 10-day forecast, keep row cover or old sheets handy, and wait until after the late end of the range, March 29 around Atlanta, before setting out tomatoes, peppers and eggplant. In north Georgia and the mountains, wait later still.
Common questions
When should I start tomato seeds indoors in Georgia?
Around Atlanta, sow tomatoes between January 28 and February 22, based on 5-6 weeks indoors counted back from a last spring frost of March 11 to March 29. In north Georgia and the mountains the last frost comes later, so start later. On the coastal plain, where the last frost is earlier, start earlier.
Can I start seeds indoors in December?
Yes, for the slowest crops. Onions and leeks go in November 26 to December 21, celery December 10 to January 4, and broccoli, Brussels sprouts, cabbage, cauliflower and head lettuce from December 24 to January 18. Peppers, tomatoes and other warm-season crops started in December would be oversized before frost danger passes.
Do these dates work for my yard if I live outside Atlanta?
Use them as a starting point and shift in the right direction. Colder places, meaning farther north or higher in elevation, have a later last frost, so sowing moves later. Milder places toward the coast have an earlier last frost, so sowing moves earlier. Your county extension office can give the local last-frost range, and the same week counts apply to it.
Do I need to start everything in the table indoors?
No. Many gardeners buy transplants of tomatoes, peppers and onions instead, and the calendar then tells them when to shop. Growing your own seedlings gives you more varieties to choose from. Sweet potatoes are a special case, since slips are shoots grown from a tuber rather than from seed, and the 6-8 weeks in the table (January 14 to February 15 around Atlanta) covers sprouting the tuber and growing the slips.