Gardeners with limited space have a new option when it comes to container tomato gardening: the grow bag. Made from plastic or polypropylene fabric, grow bags can be breathable or nonbreathable. Knowing which type you have will prevent you from overwatering. Find grow bags at your local garden nursery or order from a retailer online. Do not use garbage bags or other household bags, since there aren't strong enough to support the weight of a mature plant and soil.
Wait until temperatures outdoors have warmed up to 55 F both day and night and frost danger is past for your area. Then fill your grow bag with a potting soil mix. Gardeners.com recommends 60 qt. of mix for one of their grow bags. Incorporate a slow-release tomato fertilizer with the potting mix so that your grow bag tomatoes will receive adequate fertilization.
Poke 1/4-inch deep holes in the soil, following the spacing instructions on the seed packet for your variety of tomatoes. Place one tomato seed in each hole, then cover over the hole with potting mix.
Water the newly planted tomato seed until the soil mix becomes saturated. The seeds should germinate within one week. Place the grow bag in a full-sun location so the seeds can develop properly.
Continue to water the seedlings so that the soil remains moist but not waterlogged.
Thin out the seedlings when they have two or three sets of scalloped-edged leaves. Leave at least 14 inches of space between each tomato plant in the grow bag. You can discard the extra seedlings or plant them in another container.
Continue to water the tomatoes so they are moist but not soaked. Grow bags that aren't breathable are susceptible to becoming waterlogged, which could lead to root rot. Breathable grow bags don't have this problem.
Support certain varieties with a trellis or tomato cage by placing the trellis inside the container or moving the container adjacent to a wall trellis. The seed packet will inform you whether your chosen tomatoes need support.