When to Start Seeds Indoors in Mississippi: A Crop-by-Crop Calendar

Onions and leeks go in first, sown indoors between November 21 and December 14. Sweet potato slips go in last, between February 6 and March 1. Every Mississippi sowing date counts back from the last spring frost, which falls between March 6 and March 22 in NOAA’s 1991-2020 normals for the Jackson airport weather station. Gardens in colder north Mississippi start later than these dates, and gardens in the milder south start earlier. The calendar below gives the window for each crop.

The date everything counts back from

Knowing when to start seeds indoors in Mississippi begins with one date: the last 32°F freeze of spring. NOAA’s 1991-2020 Climate Normals for the airport weather station put it between March 6 and March 22, using the band where the probability of a 32°F freeze sits between 30 and 70 percent (NOAA NCEI data). Inside that band a freeze is neither rare nor certain, which is why a range works better than a single day.

Each crop then gets a number of weeks indoors before it goes outside. University of Minnesota Extension publishes a widely used table of those weeks, from 14-15 weeks for onions down to 3-4 weeks for sweet potatoes. You subtract them from the frost date. The calendar months in that table belong to Minnesota, so only the week counts carry over to Mississippi.

The width of the frost range changes what happens in your garden. Count back from March 6 in a yard that stays cold into late March, and your tomato seedlings sit in their pots for extra weeks. They stretch toward the window, run out of root room and arrive in the garden tired. Count back from March 22 in a yard that warms early, and you plant out later than the weather allowed. That costs weeks of growth in a state where spring turns hot fast, and it shortens the harvest of crops like peppers and eggplant that need a long season.

The airport station is not your backyard. Gardens away from the airport can see their last spring frost later than the airport does, especially in low-lying spots and at higher elevation. Colder northern Mississippi sows later than the dates in this article, and the milder southern part sows earlier. Count back from a last frost of March 6 to March 22, then move every date later if your garden runs colder than the airport. The county extension office can tell you how your area compares, and the page on First and Last Frost Dates in Mississippi covers the spring and fall dates in more detail.

Hardiness zones will not settle the question. The USDA Plant Hardiness Zone Map (2023 edition) places Mississippi in zones 7b-9a. That system rests on a single variable, the average annual extreme minimum temperature. It tells you which perennials survive winter and says nothing about when the last freeze of spring arrives, so use the frost date for sowing.

The calendar, crop by crop

The table pairs the usual extension guidance on weeks indoors with the sowing window that results when those weeks are counted back from the March 6 to March 22 frost range. Treat the weeks as standard horticultural practice, a good default rather than a law. A warm, bright setup can shorten them a little, and a cool, dim one can stretch them.

How do you read the sowing windows?

The early end of each window pairs the longer week count with the early frost date. The late end pairs the shorter count with the late frost date. A gardener in the warmer south can lean toward the early end of every window. One in the colder north should lean toward the late end, or go past it. Tomatoes, for example, go into trays from January 23 to February 15, and no earlier, because five to six weeks is all a tomato seedling needs before it is ready for the garden. The details are in Growing Tomato Seedlings Indoors.

Peppers, eggplant and okra deserve a second look. They are heat lovers, and they stall in cool soil even after the last freeze has passed. Plant them out once nights stay mild, not on the first day the frost risk drops. Okra also grows well sown straight into warm ground, so an indoor start is optional for it.

Onions and leeks take the longest, and their window opens in late November, well before most people think about gardening. The seedlings look like blades of grass for a long time, and that is normal. Head lettuce also appears in the table. Its window is December 19 to January 11, but leaf types are often simpler to sow outdoors, and Starting Lettuce explains when each approach makes sense.

Which seeds should you not start indoors?

Root crops such as carrots, beets, radishes and turnips belong in the ground from the start. Their taproots dislike being moved, and a disturbed root grows forked or stunted. Beans resent transplanting for similar reasons and sprout fast in warm soil, so there is little to gain from an indoor head start. Squash, cucumbers and melons can be started indoors, but in most cases direct sowing works as well. Their seedlings grow quickly and sulk when their roots are crowded.

The weeks above cover the indoor part of the job. For outdoor sowing dates, including those direct-sown crops, check the Mississippi Planting Calendar.

Light, warmth and hardening off

Dates only matter if the seedlings stay healthy while they wait. Three things keep them that way: strong light, steady warmth for germination, and a gradual move outdoors at the end.

Why do seedlings get leggy on a windowsill?

Winter days in the Deep South are short, and the sun sits low. A south-facing window delivers far less light than it appears to, and it comes from one side only. Seedlings respond by stretching toward the glass, producing a long, pale, floppy stem with small leaves. Once a seedling has stretched, it stays weak even if you add light later.

The fix is a fluorescent or LED grow light hung close above the seedlings and kept there as they grow. Leave it on for most of the day, since seedlings need a dark period too. A small fan on low also strengthens stems, because the gentle movement mimics wind. Long-season crops such as onions and brassicas, which spend two or three months indoors, depend on this setup more than tomatoes do.

How warm should the soil be for germination?

Seeds germinate best in steady warmth, and peppers, eggplant and okra are among the most demanding. A cool garage or a drafty windowsill produces slow, uneven sprouting. A seedling heat mat under the tray warms the mix evenly, and a plastic dome keeps moisture in until the first sprouts show. Take the dome off as soon as seedlings emerge and move the tray under the light.

Cool-season crops like cabbage, broccoli and lettuce germinate fine at room temperature, and they grow stockier if the room stays on the cool side once they are up. Peppers and eggplant like the warmth to continue.

How do you harden off seedlings?

Plants grown under lights have never felt wind, direct sun or a cold night. University of Minnesota Extension advises hardening off all plants over the last 1-2 weeks before planting out, and that time is already counted in the weeks indoors in the table above. Begin hardening off 1-2 weeks before your planting-out date.

Start with an hour or two in a shaded, sheltered spot, such as the north side of the house. Add more time and more sun each day. Mississippi spring sun is strong enough to scorch leaves that have only seen a grow light, and spring storms can shred a tray left in the open wind. Bring the trays inside whenever a frost is forecast, and water a little less during the process to toughen the plants.

What goes wrong

Most failures with indoor seeds fall into three patterns. All three are avoidable, and all three are easy to recognize when you know what to look for.

What happens when you start seeds too early?

Seedlings that outgrow their pots show it clearly. The stems are long and thin, the lower leaves yellow, and roots circle the container. Tomatoes started far ahead of schedule may even flower in the tray and then slow down once planted. The weeks indoors in the table exist to prevent exactly this, so sow inside the window for each crop. If seedlings do get ahead, move them to a larger pot, bury leggy tomato stems deeper, and keep the light close.

What is damping off?

Damping off is a group of soil fungi and water molds that rot seedlings at the base. A healthy-looking seedling suddenly folds over, with a thin, pinched, water-soaked stem at the soil line. It spreads quickly through a crowded tray. Prevent it with clean containers, fresh seed-starting mix instead of garden soil, moist but never soggy conditions, and air moving over the tray. Water from the bottom when you can. A seedling that has collapsed will not recover, so remove it and the soil around it right away.

Is it safe to plant out the week after the average last frost?

Not reliably. The March 6 to March 22 range sits in the band where a 32°F freeze is neither rare nor certain, so a freeze can still arrive after the average date. Cold soil is the second problem, and peppers and eggplant respond to it with a stalled, purplish look. Plant tender crops only after your local last-frost range has passed and nights are mild, and cover or bring in anything already outside when a freeze appears in the forecast. Other Mississippi guides cover the regional differences that shift these dates.

Common questions

Can I start tomato seeds in December?

You can, but the seedlings will wait about two months too long. Tomatoes need only 5-6 weeks indoors, which puts the sowing window at January 23 to February 15. Seeds started in December mean big, leggy plants well before the garden is ready for them.

Do I start seeds earlier in south Mississippi than in north Mississippi?

Yes. The milder south reaches its last spring frost earlier, so its windows sit toward the early end of each range. The colder north and higher ground have a later last frost, so sowing dates shift later there. Your county extension office can give you a local last-frost range to count back from.

Do I need a grow light?

For short crops like tomatoes, a very bright south window can work. For long crops like onions, leeks, celery and the brassicas, which spend 10 to 15 weeks indoors, a light is close to necessary. Window light in winter is too weak and too one-sided, and the seedlings stretch.

Which crops should I sow directly in the garden instead?

Root crops such as carrots, beets and radishes, along with beans, go straight into the ground. Squash, cucumbers and melons usually do too. Okra sprouts well in warm soil outdoors, even though it has an indoor window in the table for gardeners who want an early start.