Plant tomatoes in Missouri after the last spring frost, which falls between mid-April and mid-May depending on where you live in the state

Missouri's last frost date is not the same everywhere. The state spans two growing zones, and your location matters. In northern Missouri, the last frost typically arrives around mid-May (around May 15). In central Missouri, it comes closer to mid-April (around April 15). Southern Missouri can see frost as late as mid-May as well, though some southern counties frost earlier. Check your specific county's frost date before you plant—the National Weather Service and your local extension office both publish these dates.

Tomatoes cannot survive frost. A single night below 32°F will kill seedlings and young plants. Even temperatures in the 40s slow their growth and can damage them. Planting too early is the most common mistake Missouri gardeners make. It feels like spring, the soil is workable, but frost can still come. Wait until after your last frost date to move seedlings outdoors or direct-seed into the garden.

Key Takeaways

  • Northern Missouri's last frost date is around May 15; central Missouri is around April 15; check your county's exact date with your local extension office or the National Weather Service.
  • Tomato seedlings started indoors should be 6 to 8 weeks old when you transplant them outside, so count backward from your frost date to know when to start seeds indoors.
  • Soil temperature matters as much as air temperature—tomatoes grow poorly in soil below 60°F and will not set fruit if soil stays below 55°F.
  • If you plant too early and frost threatens, you can cover plants with blankets, sheets, or row covers the night before the freeze.

Starting seeds indoors on the right schedule

If you start tomato seeds indoors, count backward from your last frost date. Tomato seedlings need 6 to 8 weeks of indoor growth before they are ready to move outside. In northern Missouri (frost around May 15), start seeds indoors around late March or early April. In central Missouri (frost around April 15), start seeds around early to mid-February. In southern Missouri, start around late February or early March.

Seedlings need bright light—a south-facing window or grow lights work. Keep soil moist but not waterlogged. When seedlings have their first true leaves (the second set to appear), you can move them to larger containers. Harden them off about a week before transplanting: set them outside in a sheltered spot for a few hours each day, gradually increasing time outdoors. This toughens them up for the transition.

Soil temperature and when to actually plant

Air temperature and soil temperature are different things. Tomatoes prefer soil between 65°F and 75°F. In Missouri, soil warms slowly in spring. Even if the air is 70°F in mid-April, the soil may still be 50°F or 55°F. Cold soil slows root growth and can cause disease. Tomatoes planted in cold soil sit and sulk for weeks before they start growing.

You can measure soil temperature with a straightforward soil thermometer from any garden center. Stick it 4 inches into the soil in the morning. If it reads below 60°F, wait another week or two. Once soil hits 60°F consistently, you can plant. In most of Missouri, this happens a week or two after the last frost date, not on the frost date itself. Waiting for warm soil is worth the patience—plants will grow faster and stronger.

Planting outdoors directly versus transplanting seedlings

You have two routes: start seeds indoors and transplant seedlings, or buy seedlings from a nursery and transplant them, or direct-seed outdoors. Most Missouri gardeners transplant seedlings because it gives them a head start on the short growing season. Direct-seeding (planting seeds straight in the garden) takes longer and is riskier in Missouri because the season is not long enough if germination is slow.

When you transplant seedlings, dig a hole slightly deeper than the root ball. Tomatoes can be planted deeper than they were growing in the pot—they will root along the buried stem and develop a stronger root system. Space plants 24 to 36 inches apart depending on the variety. Stake or cage them at planting time so you do not damage roots later. Water well after planting.

What to do if frost threatens after you plant

Sometimes frost comes unexpectedly after you have planted. If the forecast calls for frost within a few days of planting, cover your plants. Use blankets, sheets, row covers, or even cardboard boxes—anything that traps heat. Drape the cover loosely so it does not touch the leaves. Water the soil before covering; moist soil holds heat better than dry soil. Remove covers the next morning once temperatures rise above freezing.

This works for a night or two, but if frost keeps coming, you may need to pull plants and replant later. If you have already invested in large seedlings, the cover method is worth trying. If you have only just planted seeds, it may be easier to wait and replant once the frost risk truly passes.

Variety matters for your frost date

Some tomato varieties mature faster than others. Determinate varieties (bush types that produce all their fruit at once) mature in 50 to 70 days. Indeterminate varieties (vining types that produce all season) take 70 to 85 days or longer. In northern Missouri, where the growing season is shorter, choose faster-maturing varieties so you harvest before the first fall frost (usually around October 10). In central and southern Missouri, you have more time and can grow slower varieties.

Check the days-to-maturity number on the seed packet or seedling label. Count forward from your planting date. If you plant on May 15 in northern Missouri and your variety takes 80 days to mature, you will harvest around early August—plenty of time before fall frost. If you plant a 90-day variety, you might not get ripe fruit before cold weather arrives.

Frequently Asked Questions

Can I plant tomatoes in early April in Missouri?

In central Missouri, early April is close to the frost date, so it is risky. In northern Missouri, it is too early—frost will likely kill your plants. Wait until soil warms to 60°F and your last frost date has passed. A few weeks of patience now prevents losing plants to cold.

What is the latest I can plant tomatoes in Missouri?

Plant by early June at the latest. Tomatoes need time to grow and produce fruit before the first fall frost, which usually arrives in mid-October. Planting too late means you will have green fruit that never ripens. Earlier planting gives you a longer harvest window.

How do I know my exact frost date?

Contact your county's University of Missouri Extension office—they have your specific frost date. You can also search "last frost date [your county], Missouri" online. The National Weather Service and seed companies like Burpee also list frost dates by zip code.

Can I use a frost cloth instead of blankets?

Yes. Frost cloth (also called row cover or frost blanket) is lightweight and designed for this purpose. It lets light and water through while trapping heat. Drape it loosely over plants and anchor the edges with soil, rocks, or stakes so wind does not blow it away.

Do I need to harden off seedlings before planting?

Yes. Seedlings grown indoors are tender and will wilt or die if moved straight outside. Spend 7 to 10 days gradually exposing them to outdoor conditions—start with a few hours in a sheltered spot and increase time each day. This toughens the plants so they survive transplanting.