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

For Houston, the answer runs from late October to early February, depending on the crop. Onions go into pots first, between October 22 and November 23. Tomatoes wait until December 24 to January 25. Every date comes from counting back from the last spring frost, which NOAA puts between February 4 and March 1 at Houston’s Bush Intercontinental Airport. Texas is far bigger than Houston, so treat these as a worked example. The farther north or higher you garden, the later each window opens.

The date everything counts back from

Seed packets love to say “start indoors six to eight weeks before last frost.” The sentence is useless until you know your last frost. For the Houston area, the figure comes from the NOAA NCEI 1991-2020 Climate Normals, using the Bush Intercontinental station (IAH) and its 32°F freeze probabilities in the 30 to 70 percent band. That band runs from February 4 to March 1. Write that range down, because every sowing date below is measured backward from it.

Why a range, not a single day

A last-frost “date” is a probability, not a promise. In some winters the final freeze comes in early February. In others a cold snap shows up in the last days of the range. So the sowing window has two ends, and each end carries its own risk.

Sow to the early end and you are betting on an early spring. If the weather holds you cannot plant out, and seedlings sit in their pots stretching, running out of root room and turning pale. Sow to the late end and you are betting on a late one. If spring arrives on time, your plants reach the garden weeks behind where they could have been, and in Texas that matters. Warm weather arrives fast, and a tomato that sets fruit before the heat of summer is a different crop from one that flowers into it.

A reasonable middle path for a first-time seed starter is to sow in the middle of each window, then adjust the next year based on what the seedlings did.

Texas is bigger than Houston

Houston sits at the mild Gulf end of the state. The USDA Plant Hardiness Zone Map 2023 (built on 1991-2020 normals) places Texas anywhere from zone 6a to zone 10a. That system rests on a single variable, the average annual extreme minimum temperature. It tells you which perennials survive the winter. It does not tell you when the last freeze falls, so use it for shrubs and fruit trees, not for sowing dates.

The Panhandle freezes much later in spring than Houston does, and North Texas and the Hill Country each have calendars of their own. Even within Houston there is a gap. Hobby airport runs about two weeks milder than IAH. The direction is simple: in a colder part of the state, the last frost comes later, so each sowing date below moves later too. Find your local range on the First and Last Frost Dates in Texas page and subtract the weeks yourself. More statewide planning help lives in the Texas guides.

The calendar, crop by crop

The weeks-indoors figures here come from University of Minnesota Extension’s table on when to plant seeds and how long to keep them indoors. They are the usual guidance in extension horticulture, not a law, and a few days either way will not ruin a crop. The Minnesota table also lists calendar months, but those belong to Minnesota. The windows below were computed by counting the weeks back from Houston’s February 4 to March 1 range.

Reading the table

The pattern is a staggered start. Onions and leeks go into flats before Halloween is long gone, and tomatoes wait until after Christmas. Gardeners new to seed starting tend to flip this order. Tomatoes feel like the headline crop, so they get sown first, and by February they are leggy and root-bound while the onions are nowhere in sight. Onions are slow, fine-leaved seedlings that need the long runway. Tomatoes grow fast and need only five to six weeks. For a deeper look at that crop, see Growing Tomato Seedlings Indoors.

Peppers and eggplant, at nine weeks, sit in the middle. They are slow to germinate and slow to size up, and they sulk in cool conditions, so the December window is worth respecting. Okra uses the same nine weeks in the table, though many gardeners direct-sow it once the soil has warmed.

The broccoli, cabbage and head lettuce row deserves a footnote. The weeks are counted back to the last frost for simplicity, but these cool-season crops tolerate chilly weather and are commonly planted out earlier. If you plant them out earlier, sow them earlier by the same amount. Leaf lettuces run on a different rhythm than the head types in the table, and the notes in Starting Lettuce cover them.

What should stay out of the pots

Not everything benefits from an indoor head start. Root crops such as carrots, beets and radishes resent being disturbed, and a transplanted taproot tends to fork or stall. Beans grow so fast outdoors that a pot only delays them. Squash, cucumbers and melons can be started indoors, but in most home gardens the seedlings sulk at transplanting and gain little on seed sown directly after the soil warms. For these, sow straight into the garden and skip the indoor calendar. The Texas Planting Calendar covers the outdoor timing.

Light, warmth and hardening off

A seedling that stretches is chasing light. A sunny window looks bright to us, but to a seedling it is dim and comes from one side. The stems elongate, lean toward the glass and fall over. Texas adds a twist, because a south-facing sill in December can run warm at midday and cold against the glass overnight. The temperature swing is as hard on young plants as the weak light.

Light that stays close

The cure is a light source directly above the plants, kept close to the leaves and raised as they grow. A basic fluorescent or LED shop light on a chain does the job. Seedlings under overhead light grow short, stocky and dark green, the shape you want in the garden. Windowsill seedlings, even the lucky ones, grow lean and pale. If you must use a window, rotate the trays daily and expect to compromise on sturdiness.

Warmth, then hardening off

Germination wants steady warmth at the soil level, more than air warmth. Cold, damp mix is where seeds rot and slow-starters like peppers and eggplant stall. A heat mat under the tray evens out the swings, and once seedlings emerge you can remove it and let the plants grow in ordinary room conditions. A cool garage in January is the wrong place for a pepper tray, however convenient.

Hardening off is the bridge between indoors and outdoors. University of Minnesota Extension advises hardening off all plants over the last 1 to 2 weeks before planting out. Start by setting the trays outside in a sheltered, shaded spot for a short time, then lengthen the outdoor hours and move them into more sun and wind each day. Skipping the step is a common reason healthy seedlings arrive in the garden and promptly scorch or fold. Block out the final one to two weeks before your planting-out date for hardening off, and bring trays in on any night the forecast dips toward freezing.

What goes wrong

Most seed-starting failures trace back to timing and moisture rather than to the seed itself. Three problems account for the bulk of them, and each one is easy to recognize once you have seen it.

Starting too early

The symptoms are tall, thin, pale seedlings, roots circling the pot, and plants that flower or bloom in the tray. They are stressed before they reach the garden and slow to recover afterward. The fix is to trust the table. If you are unsure of your last frost, sow nearer the late end of the window. A seedling that is a week short can catch up. A seedling that spent three extra weeks cramped in a cell tray cannot.

Damping off

Seedlings look healthy in the morning and by evening are pinched at the soil line and lying flat. Damping off is a group of soil-borne fungal and water-mold diseases, and it thrives in wet, stagnant, cool conditions. Prevention is mostly about hygiene and restraint. Use clean containers, fresh seed-starting mix rather than garden soil, water from below or lightly from above, and let the surface dry between waterings. Keep air moving with a small fan. Once seedlings fall, the ones next to them are usually next.

Planting out the week after the average last frost

The NOAA range of February 4 to March 1 describes the 30 to 70 percent probability band for a 32°F freeze, so the odds of a late freeze have not dropped to zero even at the late end. Tender crops such as tomatoes, peppers, eggplant and okra suffer from a cold snap and from cold soil, which stalls roots and leaves the leaves purple-tinged. Hold tender transplants until the forecast shows no 32°F nights, even if the calendar says go. Keep a frost cloth or old bedsheet within reach, and delay a week if the weather turns.

Common questions

Can I use these dates in North Texas or the Panhandle?

Not as written. The figures come from Houston’s IAH station, the mild Gulf end of the state. In North Texas, the Hill Country and especially the Panhandle, the last spring frost falls later, so every window shifts later. Take your own local last-frost range and subtract the same weeks from it.

Should I sow at the early or late end of a window?

The early end suits you if you have strong overhead lights and room for seedlings to keep growing. The late end suits a windowsill setup, a small space, or a gardener who wants fewer surprises. Seedlings that arrive slightly small usually catch up. Seedlings that wait too long in pots often do not.

How long do seedlings stay indoors before planting out?

It varies by crop, according to University of Minnesota Extension. Onions and leeks spend 14 to 15 weeks indoors, broccoli, cabbage and head lettuce 10 to 11 weeks, peppers and eggplant 9 weeks, and tomatoes 5 to 6 weeks. The last 1 to 2 weeks are for hardening off.

What about crops I sow directly in the garden?

Direct-sown crops follow the soil and the weather, not an indoor calendar. Beans, squash, carrots and similar crops are timed from outdoor conditions, and the Texas Planting Calendar sets those dates by region.