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When your tomato plant is 3 to 4 inches (7.6 to 10.2cm) tall, begin acclimating it to the outdoors. Over the course of 10 days, take your tomato plant to a sheltered area in your garden and let it sit. Start with a few hours on day one and add a bit more time each day. This process is known as hardening off your plant. When choosing a spot, look for an area where your plant will receive filtered sunlight, such as through tree branches, and is protected from wind and debris. In the spot you plan on planting your tomatoes, use a digging fork to loosen your soil to about 8 inches (20cm) deep. Spread about 2 inches (5.1cm) of organic compost over the soil, followed by a similar amount of balanced all-purpose fertilizer. Make sure the compost and fertilizer are evenly spread and mixed into the soil. Let the ground sit for a few days before planting. Use a ruler or tape measure to find the height of your plant from the bottom of its container to the top of its stalk. Use this number to create a hole in the middle of the area you will transplant your tomatoes to. The hole should be a few inches deeper than the plant itself. Carefully remove the seedling from its pot, being extra gentle when loosening the roots. Place the plant in the hole with only the top leaves sticking above ground. Fill the hole with soil, press it down with your hands, and water it. To help it grow, make sure to water your tomato plant immediately after relocating it. Sprinkle water over the ground until the soil is moist.
Harden off your tomato plant when it is 3 to 4 inches (7.6 to 10.2cm) tall. Mix your soil with compost and fertilizer. Dig a hole a few inches deeper than your plant. Transplant your tomato plant. Water your tomatoes after transplanting.