Weather does most of the eating. A Missouri pepper plant loses its crop to days above 90 F, to nights below 55 F, to strong sun on bare fruit and to uneven watering, and the calendar decides which one arrives first. Kansas City logs 32.7 days a year at 90 F or hotter. This page reads “what eats” as what eats into your harvest, so insect pests are not covered here. For the whole growing picture, start with Growing Peppers in Missouri.
The short answer
The hot end
NOAA’s NCEI climate normals put the mean at 32.7 days a year reaching 90 F or more at the Kansas City reference station. That is roughly one day in eleven, and the days arrive in summer rather than spread evenly across the calendar. Because they cluster, a pepper plant does not meet them as a quiet average. It meets them as a run of scorching afternoons right when it is trying to flower.
The number measures heat load, not how warm summer feels on average. A summer can have a pleasant mean temperature and still stack up many 90-degree afternoons, and those afternoons are what drive water demand and heat stress. Utah State University Extension is blunt about the consequence: pepper fruit set fails when days climb above 90 F. Flowers open, then drop instead of turning into peppers. The plant looks healthy, green and bushy, and produces almost nothing for a stretch.
A reference station is one point, and it is Kansas City. Your own garden may run hotter on a south-facing wall or a bit cooler out in the country. Treat 32.7 as a scale for how much hot weather to plan around, not as a forecast for your yard.
The cool end
Heat is only half the story, and it is the half people remember. The same Utah State University Extension guidance says fruit set also fails when nights drop below 55 F. A plant can sail through a hot week and then stall because a clear, cool night passed through.
This site does not carry summer night minima for Missouri, so there is no number here to hold up against that 55 F line. The sensible move is to watch your own nights. A cheap min/max thermometer set near the bed and checked each morning will tell you more than any regional guess. Do not estimate your nights from how far north you live or from how cold last January was. Neither one says anything reliable about a June or September night in your particular yard.
The cool end is most likely to matter just after transplanting and again as the season winds down, though only your own readings can say whether your garden actually crosses 55 F. If it does, blossoms that open that week are the ones that fail.
Choosing varieties suited to a Missouri season helps with timing, and Pepper Varieties That Ripen in a Missouri Season covers that. No variety changes the two limits above. They apply to the plant, whatever is printed on the seed packet.
When to start seed here
Peppers need a long head start indoors: Utah State University Extension puts it at 8 to 10 weeks. You work backward from the day the plants go outside, not forward from a date on a packet. Here is the arithmetic, so you can redo it for your own county.
- Find your frost window. NOAA NCEI’s normals give April 6 to April 20 for the last spring freeze, taken from the 30 to 70 percent probability band at the Kansas City International Airport station. That station sits well north of the city. The downtown station runs about five days earlier in spring, and southern Missouri is milder still. Look up the station nearest you, or ask your county Extension office, rather than borrowing this range.
- Add the soil test. Transplants go out after frost and once the soil reaches 60 F. Push a soil thermometer into the bed in the morning. Your transplant date is whichever of the two conditions arrives later.
- Convert weeks to days. Eight weeks is 56 days. Ten weeks is 70 days. That is the window you subtract.
- Count back from the transplant date. As a made-up example, say your soil reaches 60 F on May 10. Subtract 56 days and you land on March 15. Subtract 70 days and you land on March 1. Sow somewhere between March 1 and March 15.
- Test the extreme. Suppose a mild spring let you transplant on April 20, the late edge of that frost window, with warm soil to match. Seed would have gone in between February 9 and February 23. Few gardens will meet both conditions that early, and that is the point: the soil thermometer, not the frost table alone, usually sets your schedule.
- Look forward to harvest. Clemson Cooperative Extension says peppers should be ready for harvest about 70 to 85 days after transplanting. From a May 10 transplant, that points to roughly July 19 through August 3. Notice what that does: your first fruit ripens in the same weeks that summer’s 90 F days are most likely to show up.
Adjusting for your county
If your county runs a week behind the example, shift everything by a week. Start too early and seedlings turn leggy and root-bound waiting for warm soil. Start too late and you shorten the season at the end, where cool nights are waiting. The soil reading is the check that keeps the whole sum honest.
What goes wrong here
Most pepper disappointments in Missouri trace back to three failures, each with a cause you can usually identify and a remedy you can usually apply. For a deeper look at flowers that never turn into fruit, see Why Peppers Fail to Set Fruit in Missouri.
- Blossom drop. Flowers fall off and no pepper follows. The cause is a hot spell, with days above 90 F, or a cool night, with lows under 55 F. Keep a thermometer reading so you know which one you are fighting. For heat, a light shade cloth over the hottest afternoon hours can take the edge off, and steady watering keeps the plant from adding drought stress. For cool nights, a row cover draped at dusk and removed in the morning can help. Then wait. Plants usually set fruit again once the weather comes back inside the limits.
- Sunscald. Fruit develops pale, papery, sunken patches on the side facing the sun. It happens where sun is strong and the plant has too little leaf cover to shade its own peppers. Do not prune away a lot of foliage, and be careful with any heavy pest or disease cleanup that strips leaves. A thin layer of shade cloth over exposed plants can protect fruit during the hottest part of the season. Harvest scalded peppers early. The damaged spot invites rot.
- Blossom-end rot. A dark, leathery, sunken patch appears at the bottom of the fruit, opposite the stem. It is tied to uneven water and to calcium that the plant cannot move into the fruit when moisture swings between soaked and dry. Water deeply and consistently, and mulch to hold moisture in the soil. A soil test will show whether calcium is really short before you add anything. Remove affected fruit so the plant puts energy into the next ones.
The three overlap more than they seem to. A heat wave increases water demand, uneven watering follows, and sunscald hits plants that lost leaves to stress. If one failure shows up, check the other two.
Common questions
How many days above 90 F does Missouri get?
At the Kansas City reference station, NOAA NCEI’s climate normals show a mean of 32.7 days a year at 90 F or higher. Other parts of the state will differ, so treat it as a benchmark and not a promise for your garden.
When is the last spring frost?
NOAA NCEI’s normals for the Kansas City International Airport station give April 6 to April 20, based on 32 F freeze probabilities in the 30 to 70 percent band. That station sits well north of the city, so downtown runs about five days earlier, and southern Missouri is milder still. Pepper transplants also need 60 F soil, so frost is not the only gate.
Do cool nights matter for Missouri peppers?
Yes. Fruit set can fail when nights fall below 55 F, according to Utah State University Extension. This site does not carry summer night minima for Missouri, so you need to watch your own nights with a thermometer instead of assuming.
Can I keep harvested peppers in the refrigerator?
The fridge is too cold for them, and it is the mistake nearly everyone makes. Clemson Cooperative Extension lists the best storage conditions as 45 to 50 F with 80 to 90 percent relative humidity, which is warmer than a household refrigerator. Below about 45 F, peppers pit and soften from chilling injury. Under those ideal conditions they keep two to three weeks, and that is a maximum, not a guarantee.