Tomato Grow Bag Size: Gallons, Litres & Plant Types

For one full-size indeterminate tomato, a 10 US gallon fabric grow bag—about 38 litres—is a practical starting choice. A 5 US gallon bag holds about 19 litres, but should not be treated as the best size for every tomato. Compact and dwarf varieties may suit smaller containers; check the variety’s growing instructions before buying.

This tomato grow bag size guide is research-based, using University of Maryland Extension and Royal Horticultural Society guidance. We have not run a hands-on bag comparison. Recommendations depend on the plant, usable compost volume and your growing conditions.

Quick size guide for one tomato plant

Plant or container	Starting point	What to check
Full-size indeterminate tomato in a fabric bag	10 US gallons / approximately 38 L	One plant, a stable support and room for the filled bag
Dwarf or compact patio variety	Follow the variety’s container recommendation	Do not assume that all small-fruited tomatoes are dwarf plants
A 5 US gallon bag	Approximately 19 L	A commonly stated minimum, with less room than the 10-gallon option
UK pre-filled growing bag	RHS guidance allows two plants in a standard growing bag	This is a different format from a single upright fabric bag; check pack instructions

Maryland Grows’ 2026 container gardening guidance favours ten gallons over five for an indeterminate tomato. The table uses that advice as a starting point, rather than promising a particular yield.

Identify the tomato before choosing the bag

Read the seed packet or plant label for its growth habit. Indeterminate tomatoes, also called cordon tomatoes in UK guidance, keep producing long stems and need support. Determinate or bush tomatoes have a more contained growth habit. A named dwarf or patio variety gives you more useful information than the word “cherry”: cherry describes the fruit, not necessarily the plant’s final size.

If the label is unclear, look up the named variety with its breeder or supplier. Write down its recommended container size and support requirements. This avoids buying a small bag for a plant selected only because its fruit looks small.

US gallons, litres and UK growing bags

Check which gallon the retailer means. One US liquid gallon is approximately 3.79 litres; an Imperial gallon is approximately 4.55 litres. Five US gallons are about 19 L, ten are about 38 L and fifteen are about 57 L. A UK listing in gallons may therefore describe a different capacity. Use the stated litres when comparing products across markets.

Also check whether “grow bag” means an empty fabric container or a pre-filled bag of growing medium. The RHS tomato growing guide recommends one tomato in a 30–45 cm pot, or two in a standard growing bag. That does not mean every 10-gallon fabric bag should hold two plants. A diameter alone cannot tell you capacity without the container’s height and shape.

Check the space before ordering

1. Measure the filled footprint. Use the product’s filled width and height, rather than dimensions of a folded bag.
2. Plan the support. Decide where the cage, stake or cord will be secured before planting. Avoid relying on a narrow bag to hold a tall plant steady by itself.
3. Plan access. Leave space to reach the compost, water the plant and inspect its stems. A bag that fits tightly into a corner may be awkward to maintain.
4. Estimate the compost needed. Check the manufacturer’s filling directions and compare usable volume. A large number printed on a bag is not a substitute for those details.

For the wider setup, use our container vegetable gardening guide. If you are still assessing your space, begin with Start Here.

Bag size does not replace watering checks

Keep moisture reasonably consistent. The RHS explains that sharp moisture changes can contribute to split fruit and blossom-end rot, and that containers can need daily watering in hot conditions. Treat that as a reason to check the growing medium, not as a year-round daily watering rule.

Record how your own container behaves through the season. If it repeatedly dries between the times you can attend to it, reconsider the container and watering arrangement together. Our guide to watering container plants helps you assess moisture before buying extra equipment.

Common questions

Is a 5-gallon grow bag enough for tomatoes?

It is not a universal recommendation. For a full-size indeterminate plant, the Maryland source favours ten gallons. For a dwarf variety, use its specific instructions and check that the stated capacity uses US gallons if you are comparing it with this guide.

Can I put two tomatoes in a 10-gallon bag?

This guide’s 10-gallon starting point is for one full-size plant. Do not transfer a recommendation for a UK pre-filled growing bag to an upright fabric bag without checking the product and variety instructions.

Should I automatically buy a 15-gallon bag?

First check the available footprint, filled weight, compost cost and support arrangement. A larger option may fit your setup, but the evidence used here does not establish 15 gallons as a requirement for every tomato.