Chiles like long, hot days and warm nights. They need warmth and light for germination and early growth, and they flower and set fruit best when days are 8 to 12 hours long and nighttime temperatures are 60 to 70 degrees. Because they’re sun worshippers that like moist soil, chiles can demand a balancing act when planted, especially in the northern regions of the United States and in Canada.
For some general rules of thumb for growing chiles, it is helpful to divide the country into three regions based on frost-free dates and USDA Hardiness Zones. Of course, there are always exceptions to the rules, but this will give you an overall picture. Dates may vary due to weather conditions.
Growing chiles in the North
The Northern range encompasses Zones 3, 4 and 5. The dates for the last spring frost there have the longest range, from the beginning of May until the end of June. Select chile varieties that mature and fruit quickly, within 75 to 80 days.
Since the growing season is short, you need to ensure that your plants have maximum garden time to mature before warm weather ends. Germinate seed indoors about 40 days before you want to transplant the chiles outdoors; they should be just about ready to flower when it is time to set them out. Alternatively, you can buy plants that are already well established.
About two weeks before planting, cover the beds with clear plastic mulch to warm the soil. Harden off the chiles for two weeks. If necessary, plants can be set out early and protected from frost overnight with plastic milk jugs or bottles; remove them each morning. However, it is better to wait until the garden soil is warm, not cold, so that the plants suffer less stress.
In climates with a short growing season, it is worth considering mulching your peppers with black plastic, black mesh or heavy straw. These help retain moisture, keep down the weeds and reflect heat onto the plant, giving it more heat and light. An additional benefit of black plastic and mesh is that they help warm the earth around the plant, unlike heavy straw.
If cool temperatures come early and all of your chiles have not yet matured, you can protect them at night. Before dusk, cover them with lightweight tarps, or even bed sheets. Remove the nighttime covers in the morning before the sun shines too hot and creates an oven beneath them.
Growing chiles in the mid-range
The more Central range covers Zones 6 and 7. You should have your chile plants ready to set out shortly after the last frost date – early April through mid-May. You can plant them at the same time as you set out basil and tomatoes, when the ground is warming up. If the weather is cold – especially if it’s wet and rainy – wait to transplant chiles; otherwise, you risk damping off.
In areas of the central United States where the soil needs help retaining heat and moisture, it is a good idea to mulch your chile plants. Toward the end of the season, if all of the fruits are not yet mature at harvest time, you may have to cover your chile plants to protect them from an early fall frost (see above).
Growing chiles in the South
The Southern range includes Zones 8, 9 and 10. This part of the United States is where chiles grow best. The last spring frost in this region occurs sometime during early February through the end of March. As the growing season is long, there is no need to rush the plants into the ground until after the soil has warmed up. Even the peppers that take longest to produce fruit have plenty of time to mature in this region.