While we have some general information on seed starting indoors, we receive a lot of customer requests for additional tips and tricks on sowing and growing the best peppers!
When to start peppers
Most of the U.S. has a limited growing season for peppers, and should start peppers indoors 8 to 10 weeks before average last spring frost, and transplant them out when daytime temperatures are at least 70°F, and nighttime temperatures are at least 55°F. In mild climates, though, peppers can be sown directly into a greenhouse or garden soil 2 to 4 weeks after any danger of frost.
Use shallow, sterile containers with drainage (4- or 6-pack at a garden center). A deeper container can hold too much moisture.
Seed Starting Mix
Use a lightweight seed starting mix/media, and sow seeds at a shallow, 1/4" depth. Seed starting mix is sterile (unlike garden soil) and lighter than potting mix, allowing for the ideal air-to-moisture ratio.
Temperature is crucial for starting peppers. Pepper seeds germinate much faster if the soil/media is kept at 70°–90°F. At cooler temperatures, they can either fail to sprout, or sprouting may take a month. The longer seeds take to emerge, the more susceptible they are to rotting in the wet conditions or being attacked by fungus in the media. Seedling heat mats are especially helpful in maintaining warm soil for peppers. Once germinated, peppers can be grown at air temperatures of 60°F at night and 70°F during the day.
Fertilize if your seed-starting media does not contain fertilizer. No fertilization is needed until seedlings develop the second set of leaves, known as “true” leaves. (The first leaves are called “cotyledons”; they arise from the seed already formed, while the following leaves are formed using new cell growth.) Use a balanced, diluted, liquid fertilizer for seedlings. Balanced fertilizers have equal parts nitrogen, phosphorous, and potassium represented as numbers; for example, 10-10-10. Regularly applied, your seedlings will have sturdy stems, flowering will be delayed until after transplanting and when plants are larger, which is best. Large plants have more fruit-producing potential and more leaves, providing shade for the fruit, preventing sunscald. Pepper plants do not require much fertilizer, but continuing with a light application of balanced fertilizer until plants are transplanted and flower buds form is a safe bet. Once buds form, switch to a light application of a phosphorous-rich or flowering formula (higher middle number) to produce more blooms and larger fruit. A soil test is always recommended, so fertilizers can be chosen to complement existing nutrients in the garden.
Transplant seedlings into moderately sized (2”–4”) pots once they approach getting too big for their container. This may be about the time they develop 1 to 2 sets of true leaves. Transplant when roots are able to hold most of the potting soil when removed, but before roots are thick and encircling the potting media (“root-bound”). If plants become root-bound, be sure to massage some of the encircling roots apart, so they do not continue the potentially strangling pattern.
Peppers are very frost sensitive, so wait to harden off until outdoors temperatures are frost-free and settled. Soil should be over 55°F when peppers are transplanted. If your spring warm-up is lagging, use plastic mulch or season extension products like hot caps or walls of water to warm the soil.
Peppers do not set fruit in periods of extended cool temperature (below 55°F) or hot (over 90°F daytime and over 75°F nighttime) temperatures. Fertilizing with kelp or seaweed can help plants with stress from heat, drought, or transplanting.
Established peppers do best when watered deeply but infrequently, allowing soil to dry out (not to the point of wilting) between waterings.
Most peppers start out one color, often green, and ripen to another color over time. As peppers ripen to their second color, the flavor sweetens and the nutrients increase. When a plant creates fruit (which contains seeds), biologically it has “done its job”, and flowering and fruiting might then slow down. By picking some fruit early or at its first color stage, you send a signal that the plant should create more seeds, continuing the process of flower, fruit, and seed maturity.
Hot, hotter, and…
A class of compounds called capsaicin (derived from peppers’ genus name) gives chile peppers their spiciness. Capsaicin occurs mostly in the light-colored ribs (also called pith) inside the pepper. The seeds contain very little or no capsaicin, but are often hot because they come in contact with the capsaicin from the ribs. Capsaicin may have several health benefits. Some of the possibilities being studied are increased metabolism, appetite suppression, decreased heart disease, reduced pain perception, and heartburn (believe it or not!). Like your peppers hot? The more mature the pepper fruit, the hotter the pepper will be. Stress, such as drought, will also make peppers hotter. You can cause stress to the plant by cutting back on watering after fruits have started to develop so the soil stays dry, but be careful not to let the plant wilt! However, drought stress may reduce yields.
The Scoville Scale was created by Wilbur Scoville as a way to rate the spiciness of peppers in Scoville heat units (SHU) based on the amount of capsaicin in the variety. Guinness World Records regularly ranks the world’s hottest peppers, some ranking at over 2,000,000 Scoville units!
Familiar chile peppers, and their Scoville Heat Units:
Anaheim NuMex Joe E. Parker: 500–2,500 SHU
Ancho/Poblano: 1,000–2,000 SHU
Cayenne Blend: 30,000–50,000 SHU
Ghost, Bhut Jolokia: Over 1,000,000 SHU
Habanero Organic: 100,000–350,000 SHU
Hungarian Yellow Wax: 4,500–5,000 SHU
Early Jalapeño: 2,500–5,000 SHU
Jalapeño Jalafuego: 4,000–6,000 SHU
Padrón: 500–2,500 SHU
Pasilla Bajio: 1,000–2,000 SHU
Santaka Hot Asian: 40,000–50,000 SHU
Scotch Bonnet: 100,000–325,000 SHU
Serrano Tampiqueño: 6,000–23,000 SHU
Thai Hot: 50,000–100,000 SHU