Growing Tomatoes In Grow Bags – Full Guide From Seed

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Last Updated: April 7, 2023

Grow bags are an affordable alternative to plastic, ceramic, or clay pots. They are lightweight and easy to move around the garden.

No matter what you grow, you can probably grow it in a fabric grow bag. In this article, I’ll share everything you need to know about growing tomatoes in grow bags. Let’s get started!

Clone of tomato sucker shoot in new potting soil
Young tomato plant in a 5 gallon grow bag.

Choosing The Right Grow Bags

If you are set on using grow bags, you should make sure you are using the best possible type for your tomato plants. There are two main factors to consider when buying grow bags:

  1. Get a large size. Tomatoes are large plants that can make use of a large amount of soil. For best results, I recommend using 5 gallon or larger grow bags.
  2. Use non-woven bags. Most grow bags are non-woven, but it helps to check that yours are as well. This simply means that the fabric is not woven or knitted together. Non-woven materials, such as felt, are harder for plant roots to grow through.

I recommend Bootstrap Farmer’s grow bags, as they come in a variety of sizes and colors. Their 7 gallon grow bags are much more stable than the smaller 5 gallon size, so they are my top choice for tomatoes.

Other supplies for growing tomatoes in grow bags:

If you plan to start your tomatoes from store-bought plants, you can skip the seed-starting and move right to transplanting (skip ahead now).

Planting Tomato Seeds

Once you have your supplies in hand, you can get started growing your tomatoes! I like to start my plants from seed, as there are so many more options to choose from.

Tomato seeds should be sown indoors 4-6 weeks before your last spring frost date. This helps extend the growing season for larger harvests later in the year. If you live in a warmer climate, you might be able to get away with direct sowing (but not here in New England!).

Labeling tomato seedling trays
Freshly planted tomato seeds.

Plant the seeds between ⅛” and ¼” deep, misting the surface of the soil the make sure the seeds are damp. Keep them warm and moist until they sprout, ideally around 70-80°F. In ideal conditions, tomato seeds should sprout within 4-7 days, though it can take longer.

After sprouting, place your tomato seedings under grow lights, or in the sunniest window you have. If you’re using a window, rotate the plants every day or two to avoid curved plants.

After a few weeks of growth, transplant into larger pots to allow the plants to keep growing. I like to use 3.5″ square nursery pots to encourage a deep root system before moving into the grow bags.

After a few more weeks indoors, your tomatoes will be itching to move outside. Once they outgrow their nursery pots, they are ready to move into your grow bags!

Growing Tomatoes In Grow Bags

With your tomato seedlings outgrowing their nursery pots, it’s time to move them into their final home – fabric grow bags. Again, I prefer at least 5 gallons, though 7+ gallons is recommended for better stability in windy conditions.

Fill the grow bags with pre-moistened potting soil to within 2″ of the top. Then, dig out a hole wide enough for your plant’s root ball, and a few inches deeper.

Gently remove the tomato plant from its nursery pot, teasing apart the roots if they are severely root bound. If they are not entangled, don’t bother pulling on the roots.

Tomato plant in grow bag

Set the plant into the pre-dug hole in the soil, backfilling in around the roots and the base of the stem. Tamp down the soil gently and water the plant slowly to moisten the rootball thoroughly.

Tip: I always recommend planting tomatoes deeply. This encourages additional root development along the lower stem and helps prevent wind damage on tall, lanky plants.

Tips for Growing Tomatoes in Grow Bags

  • Place grow bags on a non-organic surface. Always place your grow bags on a hard surface, such as a patio, driveway, or plant holder. This will discourage the plant roots from growing through the bottom of your grow bags.
  • Place a brick at the bottom of the grow bag. If you live in an area with strong winds, you can place a brick into the bottom of your grow bags before filling them with soil. This helps keep the center of gravity low, preventing the plants from falling over.
  • Use a tomato cage for support. Tomatoes can grow to be large, top-heavy plants. Without support, they will topple over and sprawl along the ground rather than grow upright. To avoid this, place a tomato cage into the fabric pots at the time of transplanting. Alternatively, grow varieties with a smaller growth habit.
  • Plant in full-sun. Tomato plants are sun-hungry, so choose a sunny spot to place your grow bags. Always harden off young plants to avoid sun scald.

Fertilizing and Watering

As your tomatoes grow, they will use up both nutrients and water. Depending on how large the plants become, they may need more or less feeding throughout the season.

To keep it simple, I recommend you water only when the soil is dry about 2 inches below the surface. This ensures that the soil remains evenly moist without drowning the root system.

However, don’t wait for the plant to droop and wilt from dehydration! Watering inconsistently in this way is a common cause of blossom end rot and other issues.

As for fertilizer, I recommend using a nutrient-rich soil to start (such as Fox Farm or similar). Later in the season, you can add fertilizer, after the plant has used up the original nutrients in the soil.

Best fertilizer for tomato plants
Various fertilizers and amendments for tomatoes.

Tip: If you have seen blossom end rot, consider adding some bone meal to your potting soil. Mix it in thoroughly before transplanting to ensure your tomatoes have plenty of calcium. Otherwise, make sure your soil or fertilizer has calcium added.

Try to avoid over-feeding your plants. It is always best to start slow and gradually increase the concentration of fertilizer. This will prevent the plants from burning and will likely provide all the nutrients your tomatoes need.

However, potted tomatoes will likely use up the available nutrients within the first 1-2 months of growth. This means they will require additional feeding, especially later on when fruits begin to form.

Harvesting Tomatoes

After your grow bag tomatoes have been outdoors for several weeks, you should begin to see flowers forming. This is a great sign! Each flower has the potential to form a fruit.

With enough pollinators (and some help from the wind), your tomato flowers will be fertilized and turn into plump tomatoes.

But when is the perfect time to harvest?

Pick your tomatoes just as they reach their final ripe color. Most tomatoes turn from green to red, so harvest them when they turn bright red.

Large cluster of supersweet 100 tomatoes
Cherry tomatoes are a great variety to grow in fabric pots.

If you wait too long, the tomatoes become vulnerable to chipmunks and other animals, along with diseases. By harvesting the tomatoes promptly, you also encourage the plant to produce more fruits for you!

I hope this article helps you learn to grow tomatoes in grow bags. Tomato plants are incredibly resilient and strong, making them an easy choice for growing in pots. You can even clone an existing plant into multiple and expand your garden quickly!

Cherry tomato trusses from Super Sweet 100


Hi, I’m Calvin, creator of Tomato Geek. I have over a decade of gardening experience and I love helping others grow healthy plants!

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