Set the tomato plants in their jiffy cubes outside during the day time for at least a week before you plant them. This hardens the plant to weather conditions. Keep the plants in the shade during the first few days of the hardening process to keep them from getting sunburned.
Prepare the garden by digging and turning at least 12 inches of soil. Work in aged manure or other composted material for your tomato plants two to three weeks before you plant the tomatoes.
Dig holes deep enough for the transplant tomatoes, using a garden hoe. Pour about a quart of water into each hole. This not only waters the roots, but it hastens the release of natural fertilizers in the jiffy cubes.
Set the plants along with their cubes in the individual holes. Place the plant so that the lowest set of leaves is at ground level. Fill in the hole with dirt. Gently tamp the ground around the stem with your fingers to help hold the tomato plant upright.