Is a 5-gallon grow bag big enough for a tomato?

It is big enough for a determinate, patio or dwarf variety — Roma, Bush Early Girl, Tiny Tim, Patio Princess — and too small for an indeterminate one. A 5-gallon bag holds roughly 0.67 cubic feet of mix and about 12 inches of depth, which supports a plant that stops at 3 or 4 feet and sets its fruit over a few weeks. Put an indeterminate beefsteak in it and you will be watering twice a day by July and still seeing blossom-end rot.

How many gallons does a tomato plant need?

Ten gallons per indeterminate plant is the practical floor, 15 is the sweet spot, and 20 buys mainly watering slack rather than more fruit. Determinate and bush types are fine in 5 to 7 gallons. The number matters less than what it represents: root volume and, more importantly, water buffer. Doubling bag size roughly halves how often you need to water in hot weather, which is the difference between a plant that cruises through a heat wave and one that stalls.

Can you plant two tomatoes in one grow bag?

Only in a 20-gallon bag or larger, and even then a single plant in a 15-gallon bag usually out-yields two crowded into a 20. Two indeterminate plants sharing a bag compete for water and nitrogen, shade each other, and dry the mix out so fast that midsummer watering becomes twice-daily. If you want two plants, use two 10 to 15-gallon bags — it costs a couple of dollars more and yields considerably better.

Do fabric grow bags dry out faster than pots?

Yes, noticeably. The porous fabric loses moisture through every surface, not just the top, which is exactly what produces the air-pruned, fibrous root system fabric bags are valued for — and also what makes a 10-gallon fabric bag need water more often than a 10-gallon plastic pot. Compensate with size rather than with a plastic liner: go up one bag size, mulch the surface with 2 inches of straw or bark, and group bags together so they shade each other.

What depth do tomato roots need in a bag?

Twelve inches is workable and 14 to 16 is better. Tomato roots can reach 3 feet in open ground but concentrate their feeder roots in the top 12 inches, so a bag that gives them a foot of good mix performs respectably. Depth matters more if you bury the stem at planting, which tomatoes reward — they root along any buried stem section, so a taller bag lets you set a leggy transplant several inches deeper and build a larger root system from the start.

What Size Grow Bag for Tomatoes? 10 Gallons Minimum, 15

Written & researched by Elena Marsh Gardening & Landscaping Editor

Updated August 2026

Three-quarter view of a person's hands pressing seedlings into dark soil in a timber raised bed, in bright midday sun

Affiliate Disclosure

Some links on this page are affiliate links. As an Amazon Associate, we earn from qualifying purchases — at no extra cost to you. We do not buy, test, or physically handle the products we cover; our rankings come from aggregated owner reviews, ratings and expert consensus. Commissions never change our verdicts. How we rank · full disclosure.

Use a 10-gallon grow bag as the minimum for one indeterminate tomato and a 15-gallon bag if you want the plant to cruise rather than struggle. Determinate, bush and patio varieties do fine in 5 to 7 gallons. Cherry tomatoes sit in between: a 7-gallon bag works, 10 is better. The number is really a proxy for water buffer — a 15-gallon bag in a July heat wave needs watering roughly once a day, while the same plant in a 5-gallon bag needs it twice and still shows the calcium-uptake stress that causes blossom-end rot.

What size for each type of tomato?

Tomato varieties are labeled determinate (bush types that grow to a set height and fruit in a concentrated window) or indeterminate (vines that keep growing and fruiting until frost). That single label drives the size decision more than fruit size does.

Tomato type	Minimum bag	Recommended	Plants per bag
Micro-dwarf (Tiny Tim, Micro Tom)	2 gal	3 gal	1
Patio / dwarf (Patio Princess, Bush Goliath)	5 gal	7 gal	1
Determinate (Roma, Celebrity, Bush Early Girl)	5 gal	7–10 gal	1
Cherry / grape (Sungold, Sweet 100)	7 gal	10 gal	1
Indeterminate slicer (Better Boy, Big Beef)	10 gal	15 gal	1
Indeterminate heirloom / beefsteak (Brandywine, Cherokee Purple)	10 gal	15–20 gal	1

Bag diameters follow predictably: a 5-gallon fabric bag is typically 12 inches across and 12 deep, a 10-gallon is about 16 by 12, and a 15-gallon runs roughly 18 by 14. Check the listed dimensions rather than trusting the gallon label alone — manufacturers round generously, and two bags sold as 10-gallon can differ by 20 percent in actual volume.

Wide view of a person's hands pressing seedlings into dark soil in a timber raised bed, in soft early-morning light

Why does a bigger bag really help?

Not because tomato roots need the extra space in any absolute sense — they need consistent moisture. Blossom-end rot, the sunken leathery patch on the base of the fruit, is a calcium-transport problem, and university extension horticulturists are consistent that it is driven far more often by fluctuating soil moisture than by a genuine calcium deficiency in the soil. A small container swings from saturated to bone-dry within a single hot day, and each swing interrupts calcium delivery to the developing fruit. A 15-gallon bag holds roughly three times the water buffer of a 5-gallon one, which flattens the swing.

The same logic explains why growers in Phoenix or Dallas often go to 20 gallons while gardeners in Maine do fine with 10. Match the size to your summer, not just to the plant.

Close-up detail of the material being worked in a raised beds & planters project, in warm late-afternoon light

Does fabric versus plastic change the size?

Effectively, yes. Fabric bags breathe through every surface, which air-prunes roots into a dense fibrous mass and prevents the circling that plagues plastic pots — but it also evaporates moisture from the sides as well as the top. A fabric bag behaves like a plastic pot one size smaller in terms of watering frequency. If you are choosing fabric, which most container tomato growers now do, treat 10 gallons as the floor rather than a comfortable middle. Mulching the surface with 2 inches of straw and grouping bags shoulder-to-shoulder both measurably cut the loss.

Three-quarter view of a person's hands pressing seedlings into dark soil in a timber raised bed, in warm late-afternoon light

What goes in the bag?

A 10-gallon bag takes about 1.3 cubic feet of mix, and a 15-gallon takes roughly 2 cubic feet — buy by the cubic foot, not the bag, because potting mix is sold that way. Use a soilless container mix, not garden soil or topsoil, which compacts into an airless block inside a bag. Blend in a controlled-release vegetable fertilizer at planting and side-dress once fruit sets. Full details are in what to fill grow bags with.

The bottom line

Buy 15-gallon bags for indeterminate tomatoes if you have the space and the budget, 10 if you do not, and 5 to 7 for bush and patio types. One plant per bag, always, unless the bag is 20 gallons or more. For the head-to-head with rigid containers see grow bags vs plastic pots, and for how many plants a bag can genuinely carry see how many tomato plants in a grow bag. Our best grow bags roundup ranks fabric weight, handle strength and owner-reported seasons of service.

We never buy, test or physically handle the products we rank. Recommendations come from aggregated owner reviews, star ratings, review volume and expert consensus — see how we rank.

More from this hub: Raised Beds & Planters · Best grow bags · What to fill grow bags with · How long fabric grow bags last · How we rank

What Size Grow Bag for Tomatoes?