How to Use Grow Bags for Tomatoes | The Container Method

Growing tomatoes in grow bags succeeds when you choose a full-sun spot, use quality potting mix, water often, and install support at planting time.

For the full breakdown, see our best Grow Bag For Tomatoes guide.

Grow bags let you grow tomatoes on a patio, deck, or anywhere the ground isn’t an option. The fabric walls give roots air and drainage, which tomatoes love — but the mix dries out fast. Steps that matter most happen in the first ten minutes: location, soil, planting depth, and support. Get those right, and the rest is consistent watering and weekly feeding.

Picking the Right Spot and Bag Size

Tomatoes need six to eight hours of direct sunlight daily. Put the grow bag where it gets that much sun from the start — it’s heavy to move once filled. Most sources recommend at least ten to fifteen gallons (about 35 to 60 liters) for a single plant, with larger determinate varieties needing the bigger end. Two plants can go in a 60-liter bag; three in a 75-liter bag. Err on the large side — more root space means more room for water and nutrients.

Setting Up the Grow Bag for Planting

Start with an empty bag in its final sunny spot. Loosen compressed mix by shaking and kneading. Confirm or cut drainage slits — most commercial bags have them, but add more if the bottom looks sparse. Keep the bag off wet ground; in damp spots, set it on a pallet, bricks, or a bench so the bottom drains freely. Fill with quality potting mix — never garden soil, which compacts in a container. Blend in compost and a slow-release tomato fertilizer for steady food through the first month.

Planting Tomatoes Deep and Supporting Them Early

Remove the seedling from its pot. Gently tease apart circling roots. Pinch off the lowest leaves so the stem you bury is bare. Dig a hole deep enough to bury the stem up to the next set of leaves — that buried section will grow extra roots, making a stronger plant. Firm the mix around the stem, then water thoroughly. Mulch the surface with straw or shredded bark to slow evaporation and stabilize soil temperature.

Install support the same day you plant — a tomato cage, bamboo canes, or small trellis. If using a wire cage, push it into the mix rather than piercing the bag fabric from the outside; punctures can tear and weaken the bag. Tie the main stem loosely with garden twine and keep adding ties as the plant grows. Adding support later risks damaging roots and bag material.

Keeping Tomatoes Watered and Fed

Grow bags dry out faster than any other container. In midsummer heat, you may need to water every day, sometimes twice. Water early in the morning so foliage dries before night — wet leaves invite blight and fungal issues. Check moisture by pushing a finger an inch into the mix; if dry, water. Aim for even moisture, not a soaking-dry cycle. A drip system or self-watering tray under the bag cuts the daily chore. Start a liquid tomato fertilizer weekly once the first flowers appear, following the rate on the bottle.

Common mistakes: letting the bag sit in a saucer of water (roots rot), using garden soil that hardens, and skipping support until the plant flops. A little attention to setup and watering, and grow bags produce tomatoes as good as any in-ground plant.