Planting giant tomato plants requires you to choose varieties that traditionally bear large fruit to begin with. Choose heirloom varieties with proven reputations for record-setting sizes. Your giant tomato plants will also need a lot of care and attention. Tomatoes are generally heavy feeders, and plants you expect to grow giant tomatoes require even more from you as a gardener. Tomatoes of this type are usually indeterminate, meaning they will continue to grow and fruit all season. This means that you will need to continually prune and harvest them in order to keep them producing.
Start your giant tomato seeds indoors, about eight weeks prior to the last frost date for your area. Use a seed starter mix in a flat or small pots and keep moist. Set in a sunny window and water regularly. Continue the watering regimen when you transplant the tomatoes as well. They should receive about an inch of water a day in order to become giants.
Prepare the soil where you will plant your tomato plants. Dig a hole that is twice as deep and wide as the root ball of the tomato plant. Dig in compost in a 1:1 ratio to the soil and mix thoroughly.
Transplant your tomato plant seedlings carefully to the prepared holes in your garden. Squeeze the sides of the flat cells or pot (unless it is a solid pot) gently to loosen the root ball. If it is a solid pot, run a garden trowel around the outside edge of the soil to loosen the root ball. Cover the root ball completely with soil and compost when it is in the ground.
Place tomato cages, stakes or a trellis at the time you transplant the tomatoes. This way, as your tomato plants grow, you can easily train them upward onto the restraining device you have chosen. Use pieces of used pantyhose to tie up your tomato plants, as these are strong but will not harm your tomato plants' vines.
Fertilize your tomato plants according to the fertilizer's instructions. After the ground has become warm and nighttime temperatures are consistently above 60 degrees Fahrenheit, mulch around the tomatoes with black plastic mulch. Mulch helps to retain moisture and heat, and black plastic mulch retains more heat than other types.
Prune your tomato plant regularly. Choose only the strongest vines with nice clusters of flowers, and bend the suckers (smaller vines) off of the larger vines with your forefinger and thumb. Do not use pruning shears, as these leave bigger wounds in the plant and can invite diseases.