The size of the pot depends on the type of pepper and the stage of its growth. Use small pots for seeds and seedlings that are less than 4 to 6 inches tall. A small 3-inch diameter seedling pot works well for a single plant, or plant multiple plants in a six-pack divided cell style planter. Once the seedlings reach 6 inches tall, transplant them into a 12-inch diameter, 1 gallon container. Use pots with bottom drainage holes and a drip tray beneath to catch any water that drains out during irrigation.
Container-grown peppers require a well-drained, lightweight potting soil. A soilless mixture that contains peat, compost and vermiculite or perlite works well. Potting mixes that contain fertilizer are fine for seedlings and mature plants, though the peppers will need more fertilization once they begin to produce. Use mixes that don't contain additional fertilizer for starting pepper seeds.
Most indoor locations don't provide enough light to grow peppers successfully. The plants require six to eight hours of direct sunlight a day to grow well and produce fruit. Use fluorescent grow lights indoors to provide the requisite light. Leave the fluorescent lights on for 12 to 14 hours daily. Purchase an adjustable light stand so you can raise the lights as the peppers grow, keeping the light bulbs 4 inches above the top of the plants at all times.
Pepper seeds require temperatures above 75 degrees Fahrenheit to germinate and continue to grow best at warm temperatures between 75 and 85 degrees. Although keeping the plants in a warm room helps elevate temperatures, the soil may remain cooler than the surrounding air. A germination heat mat, made to warm the soil for seed starting, works well for sprouting pepper seeds. You can continue to use the heat mat after germination to maintain the proper soil temperature for optimal pepper growth.
Use a soluble fertilizer for the potted peppers. A general-purpose 20-20-20 or 15-30-15 provides sufficient nutrition for the plants to grow well indoors in the confines of their pots. Soluble fertilizer is combined with the irrigation once weekly so the nutrients reach the roots quickly. Newly germinated peppers don't require fertilization. Begin regular fertilization once the plants are two weeks old. Always refer to the label recommendations of the fertilizer before application to ensure you apply the right amount for the pepper's age and size.