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Are you completely confused by garden pot sizes? You’re not alone!
In this article, Master Gardener and Permaculturist Eliza Holcombe, will help you make sense of the varying (often conflicting) pot sizes and how to determine a garden pot’s true size & volume.
At least 10,000 of my (Eliza’s) brain cells died during the grueling research that brought you this information, so please honor their brave sacrifice by sharing the article with your other gardening friends (they’re guaranteed to have been confused by pot sizes at some point in their gardening careers)!
Also, 8 out of 9 ducks declare this post to be wonderfully engaging in spite of its non-sexy topic, “choosing the right nursery pot sizes for various plants.”
So, you should keep reading regardless of your short attention span’s vigorous objections. No, really! You’ll be missing out on some fine comedy if you behave like a grumpy goose and just click here to skip to the bullet point summary or click here to skip to our pot sizes decoded table.
Garden Pot Sizes Decoded
One of the most frequent questions expert gardeners are asked is what size pot is right for a certain plant. If you’ve ever tried to look this information up for yourself, you may have discovered that the search can be complete chaos.
First, you’ll certainly encounter differing opinions on the matter since asking 12 “expert gardeners” means you’ll get at least 13 conflicting replies. However, the most confusing part is sussing out what the advice you received actually means when you set out to brave the spiders hiding in your recycled nursery pot tower or peruse the racks of decorative planters at the local garden center.
Perhaps you’re that extra nutty crafty person planning to drill holes in Uncle Clyde’s old tin bedpan so you can situate it (and the comfy plants you tuck into it) next to the cobalt bottle tree that protects you from haints. Hey, we fully support you! Down with haints!
Okay, as an example, if you’re told to use a 10” diameter pot, does that mean a 10” pot that holds approximately 1.3 gallons of soil, a 10” pot that holds 2 gallons, or a 10” pot that holds 3 gallons? All three are common sizes sold at nurseries and vary in volume capacity based on their other dimensions.
What are trade gallons?
Alrighty, perhaps we should go by soil volume instead and recommend a 1 gallon pot. Do you choose the pots labeled “one gallon” in nurseries that really only hold 0.664 gallons of soil, or should you find a pot that you can literally fit a full gallon of soil into?
Yep, if you ever looked at a “one gallon” nursery perennial and thought it couldn’t possibly be the same size as the milk jug from the grocery, your eyes weren’t playing tricks on you. Turns out there are “gallons” and then there are nursery “trade gallons” which are approximately equal to 0.71 of a regular gallon.
Does this mean the factory is cutting corners on those little plastic pellets for the injection mold machine or are they catering to wholesale growers who want customers to think they’re buying a bigger plant while they sneakily save a buck on potting soil?!?!?!?! Watch out, Washington Post and NYT, the next Pulitzer for a major conspiracy exposé belongs to the GrowJourney blog!
Now that we’re onto the trade gallons scheme, it must mean our predicament has been solved since everyone’s container size recommendations should mean “trade gallon” pots. Whew. That would mean if you’re supposed to use a “five gallon” nursery pot, your plant actually only needs the 3.55 regular gallons of soil that a 5 trade gallon pot should hold… wait… no!
An internet search turned up nursery standard “five gallon” pots that hold 3.55 gallons, 3.68 gallons, 4.16 gallons, 4.97 gallons, or 5.03 gallons. Didn’t all the plastic pot molding corporations get the conspiracy memo? Also, now we still have no clue what size pot to actually use.
How about we turn to an old standby and look at bulletins and fact sheets released by land grant university Cooperative Extension services? After reading nearly two dozen of them from all over the country, I learned that… nobody agrees, even slightly, right down to whether it should be listed by pot volumes or pot diameters.
More University Extension services used volume, but one office might say 1 gallon for peppers while others insist 5 gallons is the minimum. For tomatoes, extension offices recommended anywhere from 1-15 gallons.
For the record, we cannot imagine growing a successful full-sized tomato plant in a 1 gallon pot!
How We Came Up With the Figures For Our Gardening Pot Size Chart
I gathered as much data as I could find, dropped the extreme numbers from both end of the scale, and came up with an average based on our personal experience and the frequency with which experts made a recommendation (if the majority of extension offices swore by a 5 gallon minimum pot for peppers, that’s what we used).
We’ve put the end results into a table for you to use as a resource (below). The table is complete with conversions into just about any volume measurement you might encounter from nurseries, garden centers, your kitchen measuring tools, or found containers that weren’t originally intended for gardening (make sure to drill enough drainage holes).
We recommend focusing on the volume of soil the pot should hold and whether or not we recommend a minimum soil depth (such as at least 10” deep for beets). The rest of the dimensions can match whatever size pot you have on hand.
If your container didn’t come with its volume labeled, you can measure it yourself by filling it within 1-3 inches of the brim with water or potting soil and then using your largest kitchen measuring tools to find out how much it holds. Plus, think of how delighted your housemates or spouse will be when they discover you dumping dirt in the Pyrex measuring bowl they use for pancake batter?
Summary Bullet Points
- We include a minimum recommended size for container gardening with all the seeds we send.
- There are no standard pot sizes (it’s chaos), so we have chosen to use: a) volume in pints or gallons (which is how most pots are sold), b) the likely diameter of pots with the correct volume (if you place a ruler across the widest part on top of the pot you get the diameter), and c) the minimum soil depth for plants that are fussy about it (like root veggies).
- If your container has no volume listed, you can figure out the volume by measuring the amount of soil you can put in it using your largest kitchen measuring tools.
- Some pots may have their volume listed in measurements other than US customary units (gallons, etc.) and you can use our easy table or an online converter to figure it out.
- There are many reasons other than aesthetics and saving space to grow in pots. Some examples include mobility (control how much sun your plant gets and keep it away from extreme temperatures), problems with the local soil (salty, polluted, etc.), or being able to grow food out of the reach of critters like deer and rabbits (such as up on a deck or rooftop).
- Plants with top-heavy growth may need to be anchored to keep it from toppling in strong wind.
- “Minimum recommended” size means you should try to use a pot at least that big, so if you can’t find that exact size just get a bigger one. Additionally, it’s possible to grow plants in “too small” pots, but your watering and fertilizing schedule will be much more demanding if you want healthy plants and a great harvest.
- When using pots with large volumes (3+ gallons), it’s a good idea to buy or mix “large container” potting soil which usually contains bulky fillers like composted pine bark or coconut coir. These fillers do not break down quickly, preventing your soil from getting compacted and anaerobic before the season ends. Our favorite pre-made organic potting mix is Black Gold.
- Most commercial “slow release” fertilizers work based on temperature, so in warmer weather it will disappear much faster than the package label claims. We like to use organic liquid fertilizers on a more frequent basis to ensure our containers get what they need. *Note: Growing in pots is different from growing in-ground (your plants’ roots and symbiont microorganisms have limited space from which to source nutrients and water), which is why we don’t recommend using fertilizers for your in-ground plants and instead recommend you focus on building biological soil fertility.
- Oh, and one other important point: you can buy pots, growbags, raised beds, organic fertilizer, and other container gardening necessities on our store here!
GrowJourney’s Garden Pot Size Table
If it’s difficult to read the information in our garden pot size table OR you want a printable version of this chart, please click here to view the original google doc.
We hope this garden pot size guide was helpful!