Best Fabric Pot Size for Growing Cannabis – Indoor VS Outdoor

The container size you use is one of the most common decisions you need to make when growing cannabis.  Container sizes are specified in gallons or liters and specifies how much growing medium they can hold.  Common consensus is that bigger containers allow you to grow bigger plants.  While this is true, there are other factors you should be considering when choosing a container size.  These factors will influence:

  • Plant Choice and Desired Size
  • Medium Moisture Retention

Let us figure out what you are trying to grow, where you are trying to grow and how much you are trying to grow then we can choose a container size.

Before we continue, just know that larger containers let a plant grow larger because:

  • The plants root system has an opportunity to potentially fill into more space (larger container)
  • More roots mean more nutrition can be absorbed
  • More nutrition absorbed mean bigger plants

The other factor that ties into container selection is the type of plant you are growing:

  • Autoflower
  • Photoperiod

Autoflowers will usually always be smaller than photoperiod plants grown in the same sized container.

Autoflowering cannabis (also referred to as auto’s) will grow vegetatively for only 30-45 days and then automatically begin to flower.

Photoperiod cannabis will continue to grow vegetatively until the plant notices that the hours of light received are beginning to shorten:

  • Outdoors this occurs naturally at the end of the season as the days naturally shorten
  • Indoors this occurs when the grower manually shortens the amount of light given to the plant

So, saying that auto’s will usually be smaller than a photoperiod version of cannabis is true because the auto’s have less time to grow and will NEVER fully grow into larger pots.

Photoperiods on the other hand will continue to grow and roots will have more time and opportunity to grow and fill in larger containers.

Plant Choice and Desired Size

Traditionally container sizes are chosen based on:

  • How big is your growing area?
  • How large do you want your plants to grow?

Both concerns are basically used to figure out how many plants you can fit in to a certain sized space and how large the plants will be able to grow.

If you are growing indoors and your grow space is 3 feet (long) X 3 feet (wide) by 6 foot (high) then you can only fit in a few different container sizes (Assuming we are using soil or coco as the grow medium – growing in fabric pots).  The following are common fabric container sizes:

  • 1-gallon fabric pot
  • 3-gallon fabric pot
  • 5-gallon fabric pot
  • 7-gallon fabric pot
  • 15- gallon fabric pot

Plant choice and desired plant size start to affect our choices now because in this space example, certain plant types (photoperiod and auto) are inappropriate for the certain container sizes.  Let us create a table to review this situation:

Growing Indoor - Fabric Pot Sizing (3ft x 3ft Area)
Container Size in GallonsMaximum Containers That Fit in SpaceRecommended
Number of Containers for Space
Auto Appropriate?Photoperiod Appropriate?Potential Plant Height
153 – 5 YesNo22 - 30 inches
342 – 4 YesNo25 - 35 inches
521 – 2 NoYes35 - 60 inches
720NoYes45 - 72 inches
1510NoYes45 - 72 inches

How I pick the right sized containers for auto’s in my space:

  • I grow auto’s indoors in 1-gallon fabric containers and know that (5) 1-gallon containers fit in a 3ft X 3ft space and grow between 22-30 inches high
  • If I moved up to a larger sized container, I would not be able to grow as many auto’s in the same sized space
  • If I grew auto’s in 5-gallon, 7-gallon or 15-gallon containers this would be very wasteful for me, I would not receive any benefit.  I like to grow more strains for variety.  Growing a larger number of auto’s makes most sense for me

How you should pick the right sized containers for auto’s in space described above:

  • If you want more variety then choose 1-gallon containers so you can grow smaller plants.  Do not pick larger sized containers
  • If you want less variety then grow 1-2 plants using 3-gallon or 5-gallon containers.  You will be fine with 3-gallon containers  
  • Growing 1 auto in this space is acceptable too.  Less plants are easier to manage and since the space will be less crowded your plant can grow larger

For sake of simplicity with a photoperiod plant example; instead of running thorough a breakdown of appropriate indoor container size options for a photoperiod grow using the same space limits as we did with the auto’s, grow 1 -2 photoperiods in 5-gallon fabric pots.

Growing Outdoor - Fabric Pot Sizing
Container Size in GallonsAuto Appropriate?Photoperiod Appropriate?Max Plants Per ContainerPlant Height
5MaybeMaybe135 – 60 inches
7MaybeMaybe145 – 72 inches
15YesMaybe160 -- 72 inches
30YesYes1> 72 Inches
100YesYes3> 72 Inches

When growing outdoors my biggest concern ismoisture retention in the growing medium.

Dry soil is bad for the plants and soil.  For a good part of the growing season, it can get very hot outside and if you are growing in smaller containers your plants will need frequent watering, especially if you use smaller containers!

Smaller containers dry out more quickly than larger containers.

One of my goals for outdoor growing is low maintenance.  If my plants are in smaller containers I need to water daily.  If I need to water daily, then I cannot go away for more than 1 day a t a time.  This is a lot of work and a big restriction!  So, when I pick a container size for outdoor growing. Larger is better.

  • 1-gallon and 3-gallon containers are too small outdoors as they dry out daily during peak summer heat
  • 5-gallon and 7-gallon containers outdoors can dry out daily too, so I avoid them
  • 15-gallon containers are the minimum size I use outdoors for auto’s
  • 30-gallon containers are the minimum size I use outdoors for photoperiods

I used to grow both photoperiods and auto’s in 5-gallon plastic buckets but it was too much work.  Heat dries out your plants quickly but so does flowering \ fruiting plants.  When plants are flowering, they are very hungry and thirsty. You will need to pay extra attention to plants grown in 5-gallon containers.  There are too many risks for me in choosing a container size that can potentially dry out in 1-2 days, so I avoid smaller container sizes now.

The only benefit of growing in 5-gallon containers is that you get to push the plants hard when the plant is flowering and demanding a lot of food and water. 

If you work from home or are home fulltime then maybe 5-gallon containers outdoors will work OK, they just require more checking and watering.

The cycle of letting your plant’s growing medium get on the dry side is this stresses the plants in a good way, signaling them to perform better because of the stress. 

Stress in a plant will cause its survival instincts to kick in and perform better because it feels threatened. Strategic stress is good for a plant.  Excessive stress on the other hand can cause a plant to underperform and possibly become sickly.

To be clear, you are not trying to deprive your plants of water or dehydrate them, instead you are making them appreciate their food and water 😊.

If your plants begin to wilt and the soil is extremely dry then you are NOT watering enough.

Regardless of the container size you eventually choose, pay attention to the weight of the container after you water.  Each day that goes by, pick up the container and pay attention to the weight compared to the day you watered.  Less water in the soil will feel noticeably lighter.  You will eventually get to a point where the container feels substantially lighter.   Paying attention to this is very helpful when figuring out when it is time to water again.

When I grow outdoors, I am not trying to “push” plants to their absolute maximum.  Instead, I am trying to grow healthy, quality, maintenance free plants. I do not want to water daily.  The minimum containers size I use is 15-gallon.

I also use grass clippings as a mulch for the surface of the soil.  3 inches of grass is used to protect the soil from the direct sunlight.  This further helps the soil retain water.  This keeps the soil cool and prevents water evaporation from the soil.

I only need to water 1-2 times weekly outdoors in containers 15-gallons and larger!

If I have the option, I will also grow plants direct in the ground.  This may be off topic as we are discussing container sizes but growing in the ground has the benefits of cool soil and water retention too.

Here is an overview of fabric pot dimensions for a popular quality brand VIVOSUN:

:- VIVOSUN Fabric Containers -:
*The following table shows the container size in gallons, dimensions in Inches and centimeters, how many containers can be purchased in a set and the cost.

**The containers are actually cylinder shaped BUT are listed below in length, width and height to make it easier for you to measure your space to see what fits best in your area
Container Size in GallonsItem Dimensions in Inches L x W x HItem Dimensions in Centimeters L x W x HHow Many Containers sold Per SetAverage Cost
On Amazon
16.3 x 6.3 x 8.07 16 x 16 x 20.55$9
29.06 x 9.06 x7.87 23 x 23 x 205$11
39.65 x 9.65 x 9.84 24.5 x 24.5 x 255$16
512.6 x 12.6 x 9.84 32 x 32 x 255$17
713.98 x 13.98 x 10.2435.5 x 35.5 x 265$18
1016.14 x 16.14 x 11.8141 x 41 x 305$21
1519.69 x 19.69 x 12.2 50 x 50 x 315$22
2019.69 x 19.69 x 15.7550 x 50 x 405$23
2522.44 x 22.44 x 15.7557 x 57 x 405$25
3023.62 x 23.62 x 15.7560 x 60 x 405$27
4526.8 x 26.8 x 18.568 x 68 x 471$14
5028 x 28 x 1971 x 71 x 481$15
10039 x 39 x 2099 x 99 x 50.5 1$17


Container Size in GallonsCubic Inches of Soil Per Individual ContainerCubic Centimeters of Soil Per Individual ContainerHow Many Containers Sold Per SetTotal Cubic inches of Soil to Fill Entire Set of Containers Total Cubic Centimeters of Soil to Fill Entire Set of ContainersTotal Cubic Feet of Soil to Fill Entire Set of Containers

:- VIVOSUN Fabric Containers -:
The following table shows the container size in gallons, Total cubic feet of soil needed to fill entire set of containers, Number of containers sold in a set, Amount of 2.0 cubic feet soil bags required to fill entire set, Amount of 3.8 cubic feet soil bags required to fill entire set
Container Size in GallonsHow Many Containers Sold Per SetTotal Cubic Feet of Soil to Fill Entire Set of ContainersNumber of 2.0 (cubic foot) Soil Bags Required to Fill Entire Set of ContainersNumber of 3.8 (cubic foot) Soil Bags Required to Fill Entire Set of Containers

  • The first chart gives you an overview of Vivosun fabric pot dimensions and pricing
  • The second chart gives you an overview of how much soil volume will fill individual fabric pots and the entire set of pots if purchased in a 5 pack (Please note that the larger container sizes are sold individually)
  • The third chart gives an overview of how much soil you need to purchase to fill the entire set of pots if purchased in a 5 pack using the 2 most popular soil package sizes (2.0 cubic feet and 3.8 cubic feet).  pack (Please note that the larger container sizes are sold individually)

For example, if you were interested in using (Quantity 5) 30-gallon fabric containers, you need 19.97 cubic feet of soil.  You would need to purchase soil in either of the following quantities:

  • 10 bags of soil sold in 2 cubic feet bags
  • 5 bags of soil sold in 3.8 cubic feet bags

Hopefully this article has revealed some useful strategies for choosing proper container sizes when planning your grow.   If you have any feedback, please submit it using the form below.

Thanks for reading.

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