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

Count backward from your last spring frost. In the Las Vegas valley, that math puts onions and leeks in pots from September 24 to October 26, and tomatoes from November 26 to December 28. Those dates belong to the warm desert floor, though. Reno, Carson City and anywhere with elevation get their last frost much later, so every window slides later with it. Below: the weeks each crop needs, a calendar built from Las Vegas figures, and how to shift it for your own ground.

The date everything counts back from

Every indoor sowing date is a subtraction problem. Take the last spring frost, subtract the weeks a crop needs to grow into a transplant, and the answer is the day to fill the trays. A wrong starting number throws off everything after it by the same amount.

The one verified frost figure here comes from NOAA’s NCEI U.S. Climate Normals for 1991-2020, which give the probability of a 32°F freeze by date. At the Las Vegas airport station, the 30-70% probability band for the last spring freeze runs from January 7 to February 1. That is a range, and it should be read as one. Before the early end, a freeze is still plausible. By the late end, most years are done with it. No single day in between is the frost date.

Keep in mind what that station is. Las Vegas airport sits in a dense urban heat island, which makes it an extreme at the warm end of the state. Reno, Carson City and any garden at elevation see their last spring frost months later than this. Treat the January 7 to February 1 range as the anchor for the Las Vegas valley and nothing more. Everywhere else, pull your local range from First and Last Frost Dates in Nevada, or call your county extension office, which tracks frost for your specific valley or slope.

Nevada’s hardiness zones won’t settle this either. The USDA Plant Hardiness Zone Map (2023 edition, based on 1991-2020 normals) runs from 4a to 10a across the state. The system rests on a single variable, the average annual extreme minimum temperature. That tells you which perennials survive a winter. It says nothing about the week the last frost lets go.

Why does the range matter so much? Sow to the early end and seedlings may sit in pots for weeks with nowhere to go, stretching, yellowing and crowding their roots. Sow to the late end and you lose weeks of growth, which hurts most for slow crops like peppers and onions that need every day of a short season. Write down your own last-frost range first, then subtract each crop’s weeks from both ends to get its sowing window.

The calendar, crop by crop

The weeks below come from University of Minnesota Extension’s table on starting seeds indoors, which lists how long each crop usually stays indoors before planting out. Treat them as standard extension guidance rather than a law. A warm, bright setup can shave a little, and a cool one adds a little. The sowing windows are those weeks counted back from the Las Vegas airport frost range of January 7 to February 1. Minnesota’s own calendar months don’t apply here, so they are left out entirely.

Read the table from top to bottom and the calendar tells a story. The slowest crops go first, in early fall, and tomatoes come near the end of the year. Onions and leeks need a head start of roughly three and a half months, which surprises people used to buying tomato plants in spring and assuming everything works that way. Sweet potatoes bring up the rear, started only a few weeks ahead of planting out.

The colder the garden, the later every window opens and closes. A Reno or Carson City grower uses the same weeks but a later frost range, so the dates in the right-hand column all move later. Take your own range from the frost dates, subtract the weeks in the middle column, and you have your calendar. The Nevada Planting Calendar shows what goes in the ground afterward.

Head lettuce sits in the 10-11 week row, which is longer than most people expect for a salad crop. Many gardeners skip indoor starts for loose-leaf types and sow them outdoors, since they grow fast and tolerate cool weather. If you do want a head start, the notes in Starting Lettuce cover the details. Tomatoes get a closer look in Growing Tomato Seedlings Indoors, because 5-6 weeks is short enough that sowing too early is the most common mistake with them.

Crops that should stay out of the seed tray

Root crops such as carrots, beets, radishes and turnips resent transplanting. Disturb the taproot and you get forked, stunted roots, so sow them where they will grow. Beans and squash are the other usual exceptions. They sprout fast in warm soil, grow quickly, and sulk when their roots are cramped in a pot, so in most cases they do better sown directly after frost danger has passed. Start tomatoes indoors in the Las Vegas valley from November 26 to December 28, and push that window later in colder parts of Nevada.

Light, warmth and hardening off

A sunny windowsill looks like a perfectly good nursery, and it is where most leggy seedlings come from. Light through glass arrives from one side, and winter days are short. Seedlings stretch toward the source, grow tall and pale, and flop over. The sowing windows above fall between late September and early January, which includes the shortest days of the year, so a window alone rarely carries a crop for 9 or more weeks. A grow light hung just above the seedlings, raised as they grow, gives even light from overhead and keeps stems short and thick. Stems can be pinched and fixed only so much once they have stretched, so prevention is the real answer.

Warmth is the second piece. Germination wants steady warmth at the soil level, which is not the same as a warm room. A tray on a cold windowsill or a drafty garage floor can sit for days without sprouting while the seed rots. A heat mat under the tray evens out the temperature, and the crops differ in how much they need. Peppers, eggplant, okra and tomatoes want a warm start, and cool-season crops like broccoli, cabbage and head lettuce sprout in cooler conditions and can suffer if cooked. Once seedlings are up, move them off the mat and into good light.

Hardening off is the step people skip when spring turns warm and the transplants look ready. Indoor seedlings have soft leaves that have never seen direct sun, wind or a cold night. Nevada makes that harder than most places: intense sun, dry wind and a big swing between daytime highs and nighttime lows, especially in the high desert. University of Minnesota Extension advises hardening off all plants over the last 1-2 weeks before planting out. Start with a few hours in a sheltered, shady spot, then add more sun and more time each day, and ease off on watering a little near the end. Harden off every transplant over the final 1-2 weeks before it goes in the ground.

What goes wrong

Starting too early is the most common failure, and it looks the same every time. Seedlings outgrow their cells, roots circle the bottom of the pot, leaves yellow, and stems get long and weak. A tomato that spent 10 weeks in a tray when it needed 5-6 will establish slower than a younger, sturdier plant. The fix is to trust the calendar, use the later end of each window if your light is limited, and pot up if a delay is unavoidable.

Damping off is the other classic. A fungal problem in cool, wet, stagnant conditions, it shows up as seedlings that look fine one day and are pinched at the soil line and collapsed the next. Once it starts, it rarely stops, so prevention does the work: clean containers, fresh seed-starting mix instead of garden soil, watering from below and letting the surface dry, and a little air movement from a small fan.

The last mistake comes at transplant time. The average last frost is the middle of the odds, not a guarantee. In the NOAA band, the late end of January 7 to February 1 is when most years are clear, and in colder parts of Nevada the same logic applies to a much later date. Tomatoes, peppers and eggplant planted the week after the average date can still meet a frost, and even without one, cold soil stalls them. Plants sit, purple and stunted, for weeks. Plant tender crops out after the late end of your frost range, and keep frost cloth handy.

Common questions

Can I use the Las Vegas dates in Reno or Carson City?

No. Those windows are counted from the Las Vegas airport frost range of January 7 to February 1, a warm desert extreme. Reno, Carson City and higher ground reach their last spring frost months later, so every sowing date moves later too. Keep the weeks from the table, find your own frost range, and count back.

When should I start tomato seeds indoors in Nevada?

Tomatoes usually need 5-6 weeks indoors before planting out. Counted from the Las Vegas frost range, that gives a window of November 26 to December 28. Colder parts of Nevada sow later. Subtract 5-6 weeks from your own last-frost range.

Do I really need a grow light?

For short crops like tomatoes, a bright south window may do. For anything that spends 9 weeks or more in the tray, such as peppers, eggplant, onions and brassicas, window light usually produces leggy seedlings. A light hung close overhead is the dependable fix.

Which crops should I skip starting indoors?

Root crops, beans and in most cases squash do better sown directly in the garden, since they resent root disturbance and grow fast once the soil warms. More Nevada guides cover what to sow outdoors and when. Fall-planted garlic and onion sets are also common choices in many parts of the state.