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Once your chilli plant seedlings have reached about 2 inches (5 cm) and have 5-6 leaves, transfer them to a larger area so their roots don't get constricted. Gently lift them from the tray. Make sure to disturb the roots as little as possible. Water the seedlings before removing them to ensure that the compost doesn't fall apart during the transfer. Find a pot that is approximately 2.75 inches (7 cm) in diameter and fill it with compost. Water the compost lightly and make a well in the center of it. Gently place a seedling in the empty space and fill around it with compost.  If you live in a cooler climate, plant chilli plants in pots and keep them indoors. Set them under grow lights in a warm room. Chilli plants can be transferred from pots to a garden whenever the weather and the soil are warm enough. As your chilli plant grows, transfer it to bigger pots. Prepare a larger pot by filling it with with compost, then make a well in the center. Gently dig out the plant, leaving a large clump of compost around its roots to protect them, and place it in the larger pot.  If you wish to keep your chilli plant small, keep it in a small pot to thwart further growth. The standard progression of pot sizes goes from a diameter of 2.75 inches (7 cm) to 6 inches (approximately 15 cm), then finally to 8 inches (approximately 20 cm). Place your potted chilli plant near a window, or outside to get sunlight, making sure to bring it back inside if the temperature drops. The amount of light the plant receives will directly affect the speed and size of its growth. If you keep the plant indoors in a home that doesn't get much natural sunlight, purchase a mini greenhouse or artificial light (available online or in gardening centers).

Summary:
Remove the seedlings from the tray. Plant an individual seedling into a pot. Upgrade the size of pot you use, as needed. Make sure your plant gets warmth and light.