Square vs. Round pots

I had a google, top 10 or more hits were from the Cannabis forums (nothing like a high-value crop to strive for an ounce more efficiency!)

My thoughts:

Square will fit neatly on the bench. One advantage of this is that no light gets to the bench, which can be an advantage if you have cappiliary matting or similar as the lack of light stops muck growing there. But I think it also keeps the air between the pots cooler if they fit tightly.

For a "given size" you can fit more round pots into a given space (using staggered rows). This only works for a decent area, for narrow benches the offset system will probably be crying out for "half a pot" at the end of each row!

"decent size" means diameter for round and edge length for square.

A round pot has less volume to compost for its diameter size than a square pot's edge length.

Once the plants get to a decent size they pots will need to be moved further apart then "touching", so its only really an issue when the plants are small - particularly when first pricked out. That is also a critical time when most of us have excessive numbers of plants / pots and limited space!

Square pots provide more area for seed sowing, so they have merit there. Personally I prefer seed trays (including the 1/2 and 1/4 size ones) that are very shallow - less seed compost required, and the seedlings are only in them for a few weeks before being pricked out.

I personally think that potting-on is easier with round pots that square ones - and particularly that potting on a square into a round is a faff. I tend to use a spare pot as a template, within the new larger pot, and fill compost around it and then knock the plant out and drop it into the ready made hole. Square ones tend to snag, and there are more air gaps around where the various intrusions in the base of the original pot were etc.

For long term the Cannabis growers thought that square was better - more compost for the plant, in the long term.

However, there is an argument that roots go straight down when they hit the edge of a square pot, and circle in a round pot. For situations where that critical Air Pots are probably the better way forward.

Nurseries have a mix. Small plants are often sold in square pots, larger plants in round. They seem to be predominantly Black in colour, keeping light away from the roots, but can get hot if in direct sun. Black probably has better UV tolerance and longer life? Or its an easier colour to make from recycled plastic perhaps? Orange pots must just exist from the throw-back to Terracotta pots? I seem to have more and more black pots now, as I haven't bought Sankey originals for years favouring whatever I can buy cheaply on eBay ...

Any definitive scientific comparison that anyone has seen pls?

 

I've seen that often said, can someone explain to me what it means?

9cm rounds will squeeze more in per unit area than 9cm squares, surely?

9cm squares hold more compost volume than 9cm rounds, but I have never thought that was of concern to me? Maybe it should be?!!

Yup, I have done that too. I just find it slower, when I have lots to do, than:

Fill a spare pot (same size as original) to the brim (as a template)
Put small amount of compost in new sized pot
Stand "template" in new pot, on that compost base
fill around the template to the brim
Firm very slightly (I don't like to firm my transplants in at all, I find they develop faster without, but obviously there must be no wind or moving stuff around that would cause them to rock about before they are well rooted)
Remove template
Knock plant out of original pot and drop into hole left by template
Done!

 

Example to illustrate what I meant:



Round needs half-a-pot more width (which obviously favours wider rows, rather than short ones)

Round gains one row ever 6 (if my drawing is accurate!) which is about 17% more pots - assuming the half-pot per row is not an issue.

 

http://en.wikipedia.org/wiki/Bin_packing_problem
Packing efficiency is quite a hefty science as companies try to maximise their storage and reduce packing . But that aside I usually have my pricked out plants stored in gravel trays , and at a squash you can get 12 x 9cm squares into one. 7cm round ( vending cups ) I can get 18 in a tray. I prefer square pots and 6 cell trays they seem more space efficient and stable.

 

For round objects of identical shape I think it just needs a bit of Trigonometry?

The centres of the pots are 1 unit apart, so an equilateral triangle (red) of angle 60 degrees.

So the row spacing (green) is 30 degrees, and thus 0.87 units - which is 15.5% more rows, which seems reasonable given my 17% guestimate earlier.



Still "wastes" half a unit per row, so only worthwhile with longer rows. A square 2' gravel tray is probably not wide enough to have any gain, unless by serendipity staggered rows just happen to allow exactly one extra row to be contained, as otherwise some space would be blank

So for gravel trays picking a pot size where the rows exactly fit would be ideal - square or round . I do have that issue (I use gravel trays after pricking out), but then when the pots move to greenhouse benches they are on capillary matting, and out of the gravel trays, so to get the maximum number onto the bench, and given that I then have long row-length, I reckon? that round pots win.

 

With you on that, particularly as the plants grow and bush up as it then becomes harder to see where the pots actually are - much easier if I am watering where I know a row of pots should be, rather than if the pots were arranged haphazardly.

 

The pots I use are 75mm (at soil level) internal diameter TEKU round pots that I get for free and another make of square pot that's supposedly 70mm square, but that's the outside dimension and it's only 60 x 60mm internally and that I buy.

I'll only use the square pots in propagators or under lights (including those which are getting 'top ups' under lights) to maximise use of expensive space. Everything then gets potted up into round pots because:

1) I don't have a source of free square pots.

2) I can get thousands of used 75mm diameter pots for free.

3) Square pots are a PITA to space apart when the plant needs more space than the surface area of the pot.

4) I can get hundreds of used/free 300 x 525mm TEKU trays that take 18 x 75mm diameter free pots, which makes spacing/rotating/transporting a doddle. (and I know the pot layout under the plants)

5) I plant out using a bulb planter and plants in round pots simply drop into the hole.

6) If plants get sold they're in a free round pot, not something that has cost me 5p.

 

Interesting point. Can you explain why Square are more trouble in that regard pls? I use round so hadn't considered the difference, but my guess would have been that square would be more stable once spaced out [larger footprint]?

Forgotten that benefit. You are SO right. A 3" or even 9cm round pot exactly fits my leap-up-and-down-and-stamp-on bulb planter, and I can drill holes and plant out loads in a short time.

A good point, but I think relevance restricted to having multiple plants (particularly seeds) in a pot? If you have one plant per pot is it relevant whether round or square if either will get you, say, "10 pots per square metre" ? (Apologies for splitting hairs, but I'm looking for the devil in the detail )

 

When there's hundreds of plants I find it more convenient/cheaper to use/pick up/shift trays (obtained free) of 18 round pots rather than laying out grids of bought square pots in bought gravel trays and experiencing pots moving about or breaking leaves checking where the pots are.

As for pots in propagators/under lights I find keeping everything square/rectangular enables me to cram the most stuff in, as I cut up cellular tray inserts into smaller blocks/strips that fill every gap between the square pots.

 

Yes, I use pot-carriers too. Makes a huge difference with the amount that I grow compared to using gravel trays and the like. But once they get onto the capillary matting benches I need to maximise the population so I take them out of the carriers and arrange them as snug as I can to get maximum density.

I use gravel trays for newspaper pots (Sweet peas, Parsnips and Sweet corn only) and anything in odd shaped pots Bought another 1,000 9cm pots this year to avoid any odd-shaped-pots; odd shaped pots will be used for anything I am growing to give away - in the hope that the odd shaped pots don't come back again for another season! but I can never bare to throw away pots that come with pants that I buy-in, and that bulks up my odd shaped pots collection ...

 

The majority of my pots are based on what other people throw away, so as to which ones are best, square or round is a bit immaterial.
But I would guess when cramming pots close together square ones allow more compost per plant for the given area.

 

Hmmm ... so if I changed from, say, a 9cm round to an 8cm square, I would get more pots in, but each plant would have the same compost pot volume (volume of 9cm round is pretty much the same as 8cm square).

9cm round would give me 13 x 15 (per sq.m.) in a staggered arrangement
8cm square would give me 15 x 15

Plants only 8cm apart though, so a bit less growing room.

I think I've split the hair too much at this point!

 

OK so why are pots so tapered, if the pot was only very slightly tapered you could get more compost in it, but it would still take up the same space.