Pepper seed germinates fastest at 85°F soil temperature, and the plant that grows out of it wants 70 to 85°F days with nights above 60°F until the last pod colors up. Those two numbers carry most of the season. The rest of this page covers where each species departs from them, and C. pubescens departs the furthest.

What temperature do pepper seeds need to germinate?

J.F. Harrington at UC Davis measured it directly, and his table still sets the standard. Pepper seed will not move below 60°F. It germinates across 65 to 95°F, peaks at 85°F, and stops again at 95°F. The speed penalty for running cool is brutal.

Soil temperature.Days to emergence.
50°F and below.Little or no germination.
59°F.25 days.
68°F.12 days.
77°F.8 days.
86°F.8 days.
95°F.9 days.
104°F.Little or no germination.

Soil temperature is the figure that counts, not air temperature. A propagation shelf reading 75°F on the wall thermometer can hold a 65°F root zone, because a dense starting mix in a plastic tray wicks heat away. Put the probe in the medium. A heat mat with a thermostat and a soil probe solves most germination complaints before they start, and the germination chart lists the species spread in detail.

Targets by species and stage

Figures for the five domesticated species come from the Harrington table and from The Chile Pepper Almanac. The wild rows come from the Almanac's native-habitat tables, compiled from grower trials rather than from replicated studies, so treat them as starting points and watch the plant.

Species.Germination.Day, seedling to vegetative.Night minimum.Fruit set range.Winter floor.
C. annuum, cultivated.80 to 85°F.70 to 85°F.55°F.65 to 85°F.50°F.
C. annuum var. glabriusculum (tepin).85 to 90°F.70 to 90°F.55°F.65 to 90°F.50°F.
C. chinense.82 to 90°F.75 to 90°F.60°F.70 to 90°F.50°F.
C. chinense, superhot selections.85 to 95°F.80 to 90°F.65°F.75 to 95°F.50°F.
C. baccatum.78 to 86°F.65 to 85°F.50°F.60 to 85°F.50°F.
C. frutescens.78 to 86°F.75 to 85°F.60°F.70 to 90°F.50°F.
C. pubescens.65 to 78°F.60 to 75°F.40°F.50 to 75°F.40°F, hardy near 35°F.
C. chacoense.86 to 90°F.75 to 95°F.55°F.No published figure.50°F.
C. eximium.84 to 88°F.60 to 75°F.45°F.No published figure.Light frost reported.
C. cardenasii.84 to 88°F.60 to 75°F.40°F.No published figure.Near freezing reported.
C. galapagoense.75 to 85°F.75 to 90°F.60°F.No published figure.50°F.
C. tovarii.75 to 85°F.55 to 70°F.45°F.No published figure.Fails in heat.

Why rocoto breaks every rule

The old version of this chart put C. pubescens germination at 65 to 75°F and left it there as a curiosity. The more useful framing: heat kills it. Rocoto seed germinates from roughly 65 to 78°F, and the same bottom heat that rescues a stubborn C. chinense tray will cook a rocoto tray. The plant carries that preference through its life. It stalls above 80°F, needs cool nights to set fruit, and lives 15 years or more where summers stay mild. Growers in Andean highland climates and cool maritime summers get better rocotos than anyone in Texas. See the Rocoto record for the species profile.

Seedlings and vegetative growth

Once the cotyledons open, drop the temperature. Holding germination heat produces stretched, leggy seedlings that fall over. Days of 75 to 80°F with nights near 65°F give short internodes and thick stems. A 10 to 15°F day-night swing helps, which is one reason plants under a single fixed thermostat often look softer than plants on a windowsill.

Through vegetative growth, C. annuum handles 70 to 85°F without complaint and slows below 50°F. C. baccatum is the most cold-forgiving of the group and keeps growing where annuum sulks. C. frutescens and chinense want warmth and humidity together, and both drop leaves after a week of nights in the low 50s.

What night temperature causes blossom drop?

Below roughly 55°F, fertilization fails even when the pollen looks fine, because cold slows pollen tube growth. Above the other end, the pollen itself goes. Pollen viability falls off sharply past 90°F and collapses near 95°F. Erickson and Markhart exposed bell pepper to 33°C, about 91°F, and found reduced fruit set in flowers that reached anthesis during the exposure, with 48 hours enough to do it. Buds under 2.5 mm long at the time of exposure produced less viable pollen later.

That gives you a working window: days 70 to 85°F, nights 60 to 70°F. Peppers tolerate excursions. What they will not tolerate is several consecutive days outside the range during flowering, which is how a plant covered in blooms ends up holding four pods. Shade cloth at 30 to 50 percent buys back several degrees in a hot spell, and growing peppers in extreme heat covers the rest.

Ripening and overwintering

Fruit fills and colors fastest between 75 and 85°F. Below 60°F, development stalls and maturity stretches out by three to four weeks. Above 95°F, pods sunscald and color bleaches. Hot, dry conditions during fruiting also push capsaicinoid content up, which is why the same variety tests hotter in a drought year.

For overwintering, the target is survival rather than growth. Keep the root zone above 50°F, cut water back hard, stop fertilizing, and give enough light to hold some leaves. C. pubescens tolerates a colder shelf than the rest. The overwintering guide covers pruning and the spring restart, and germination timing by species sets the calendar for starting again.

Sources & Further Reading