Plant tomato plants as early as possible to grow very large tomatoes; a few weeks to a month before your last expected freeze date, advises Gordon Graham, the Guinness World Records title holder for the largest tomato. Organic Magazine recommends starting with indeterminate (varieties that produce throughout the season) tomatoes known to produce large fruits, such as Giant Belgium, Hillbilly, or Big Zac.
Till your garden, in an area with full sun, to an 8-inch depth. Use a rake or rototiller to break up the soil with its tines.
Sort through the soil by hand, removing rocks and weeds and any other debris. Dispose of these items in an outside trash container or trash bag.
Shovel a 1- to 2-inch layer of compost on top of the soil. Re-till the area to mix the compost into the soil. Again, work down to a depth of 8 inches.
Dig a hole with a shovel for each plant. Dig holes deep and wide enough for the roots of the plant and up to its base. Space holes according to the directions provided with your tomato plants.
Set each plant in its hole. Spread out the roots of the plant in the hole. Pack the soil on top of the roots and up to the first set of leaves on the plant.
Place a strong, tall, steel tomato cage around the perimeter of the plant. Choose a cage at least 6 feet tall as many of the larger tomato plants grow to be over this height.
Place a protective cover, like a cloche, over the plant. When planting early, tomato plants need protection from nighttime freezing temperatures. Remove the protective cover once all chance of frost has passed and when nighttime temperatures average over 50 degrees F.
Water plants daily, unless the soil appears moist. Skip watering on days it rains.
Fertilize the plants every two weeks with a fish emulsion fertilizer, available at nurseries or garden centers. Follow the directions provided with the fertilizer to determine how much fertilizer to use.
Pinch off suckers, the flowers in the "Y" between the main stem and the branches, as soon as they develop. Leave only one stem on the plant to form fruit.