What succession of sizes of plug trays, flats and pots do you use?

For those with an organised system of standardised pot sizes for successive potting on of young plants (not those who use any old pot).

What succession of pot sizes (cm) do you use for potting on?

My store of pots is an mess again, higgledy-piggledy, trashed pots, gastropod Centraal and more-importantly space-hogging and time-sapping. Hardly a dozen pots the same, apart from the neatly-stacked 8cm rounds which were presumably bought as bulk packs, and pots and planters 19cm diameter and above because I bought every one up in the supermarkets when they were practically giving tem away.
So I'm putting together a bulk pot order of durable, reusable potting-on pots that'll last many years. Weighing up the ranges of teku v desch

What do you use for seed starting?

I'm using a mix of Danish, Euro, Standard and domestic sized flats and plug trays but will be standardising, probably on the Danish, because there is the largest range of plug shapes and sizes, I'm basing my staging racks on Danish trolley dimensions, and if I buy in, most supply chains use Danish (Dutch) rather than Euro.
The flats (designed for automated lines) are much easier to store as they are flat top and bottom so no need to nest them. They are, however, better-suited to COTS pelleted media mix or homemade bound media than a freeflowing media.
I usually start off smaller seeds in 32mm round (conic down to 16mm) flats then onto pots, but use 50mm square cheapos for larger seeds which fall apart too easily so I'll finish them up and get proper ones to reduce waste.

 

I sow into 1/4 size seed trays - sometimes 2 or 3 varieties per tray, but they always go at different speeds and need pricking out at different times, so where I only have 5 seeds or so then I use a 9cm square pot instead (actually, more often with small seed volumes I use a small zip-lock bag and a couple of teaspoon fulls of just-damp Vermiculite - particularly if the seed needs stratification.

I have been pricking out to 1" modular cells, but I hate them. The cheap ones are impossible to get the plants out of, for potting-up, without major root disturbance, and the good quality ones I have (with a decent hole in the bottom that you can push-up through with the blunt end of a pencil) are too big - I never have that many plants of a single variety, so I wind up having potted-up 50% of the tray, and then having to find bench-space for the whole tray, wasting large areas.

I've had the discussion here before about using short lengths of 1" pipe instead of cells, but folk were not encouraging, but I really really need to try that, if only to fail, as it would suit me much better. Unlimited expansion from 1-plant to nnn-plants. They can sit on the capillary matting happily, perhaps with an elastic band around a batch of half a dozen or so, and I can have longer (i.e. deeper) ones for those seedlings that head straight down. I think they will be easier to pot-up too ... but ... the pipe will be straight sided and I don't know if that will make it difficult to eject the plugs??

Anyways, from there I go to 9cm round pots. I used to use 3" but they were too small if the plants needed "holding" a bit before planting out, and I find that 9cm gives me just a bit more wiggle-room. Plants that go straight out from there (bedding plants in spring) I plant with a bulb planter (the sort that looks like a Pogo stick that I can jump on with both feed, and saves my arthritic wrists compared to trying to use a trowel).

If potting-on I go from 9cm to 1L, then usually 2L, 5L but occasionally from 1L to 3L if I can then go outside from there.

Rooted cuttings are potted up to 9cm.

I have tray-pot-holders so I can easily carry 4x5 x 9cm (20-off) and 3x4 x 1L (from memory) and 2x4 or maybe 2x5 x 2L which I got from a nursery clearance. Makes a huge difference, for example, when hardening off and a load of plants need moving in & out each day/night.

 

I always sow into half size seed trays sitting in full size trays and some times divide these between 2 different seeds with 2 labels in the middle. As half trays get pricked out, the remaining half trays get consolidated into a lesser number of full size trays. I also use 15x and 24x cellular tray inserts sitting in full or half size trays with different seeds in each module which either have a separate label in each cell and for seeds with different germination times/growth rates I cut the cells into strips so they can be pricked out separately. Cells take much less expensive seed compost to fill than standard pots.

For larger seeds such as runner beans (15x deep trays), peans, french beans (24x trays) I will sow in cell trays and grow on until they're big enough to plant out, the same with any other seeds (individual and multiples for clumps) that will not be pricked out and will be grown on to transplanting size in the cells. Marrows, pumpkins, cougettes, squashes and cucumbers get sown in 70mm (60mm at soil fill level) pots (square ones for most efficient use of heated propagator/growlight space)

If seeds are being pricked out to be put under expensive growlight space I transplant the seedlings into either 40x /24x cell trays (depending on size of seedling/rate of growth) or 60mm Flexipots (AKA breeder pots) which are flexible polythene pots that can be squeezed together to get lots in half or full size trays, and these being deeper than cell trays allow the likes of tomatoes to be buried deeper.

Other than those grown to planting out size in cell trays, most plants for planting out in open ground get potted up into 80mm diameter (at soil fill level, so might be 90mm 'nominal') pots (in 18x pot trays) as they will be ideal for dropping into holes formed using a bulb planter, the only exceptions I can think of are pumpkins and marrows which will be potted up so they're in decent size pots by the time the danger of frost has past.

Stuff like tomatoes for planting in polytunnels will be potted on into larger pots as these are sown earlier than those for growing in open ground and would be far too big for 80mm pots. Parsnips are sown in soil filled toilet rolls tubes, kept in a polytunnel and the whole tube planted out as soon as the leaves show (any later and the root will be out the bottom and the parsnip will fork).

My sources of pots, etc. are 80mm (at soil fill level) round pots and 18x pot trays I can get by the thousands from a gardener who works at a place where they have mass bedding displays, and from Wilkos when reduced, such as several weeks ago when I got loads of packs of pots, seed trays, etc. at 1p per pack, and yesterday when I got packs of three 24x cell trays at 20p per pack (0.28p per cell).

EDIT: A bit late for pics/details of seed sowing, pricking out, potting up, etc. through to planting out, but I'll save the link add some stuff starting early next year, as it might be interesting to compare how other people sow, etc.

 

Interesting @Scrungee

I re-use my seed sowing compost year-after-year. It needs no nutrients, so I just moisten it and microwave for 10 minutes, mixing well after 5 mins (for the largest bowl that comfortable fits in the microwave)

Ah, forgot about them! Runners and Climbing French I grow 2 plants per 9cm pot and plant out as-a-pair, with a single cane. I also sow-a-seed when I plant out for a follow-on plant & crop a month or so later.

I am convinced that is "debatable". I think I get more round ones in by using on a triangulated-diamond pattern. Personally I find round pots much easier (as in quicker) to pot on, and of course they fit my circular bulb planter better than square ones would

Same here, except I make pots by rolling a sheet of newspaper around an aerosol can - that allows me to to make pots that are a lot taller than loo-rolls, which gives me some extra time before planting out - I harden off the moment the seed leaves appear and it is about 3 weeks before the first true leaf appears, which seems to also be the time that the tap root comes out of the bottom, so I aim to plant out 2 weeks after true leaf appears, or as soon as hardened off if that is sooner. But its basically just the same method

 

I seem to have enough trouble with mould growing on the surface of seed compost when sown under propagator covers (especially with saved seed debris), without added 'cooked' root remnants, partially/un-germinated seeds, etc.

Square pots have got to be more efficient as there's no wasted space between them.

Standard bulb planters only create holes suitable for 70/75mm diameter pots. Long handled ones are a right PITA for using to plant through membranes as the soil (unless sufficiently moist/compact to work with them, otherwise it will fall out all over the membrane surface as you can't grip it on retraction like you can do with a standard spring loaded planter). And even then it's another PITA having to lift up and physically poke out the plug of soil in a long handled planter when a standard hand operated one will release the soil with a squeeze of the handle.

 

More soil-per-plant, sure. A 9cm diameter is going to take up no more bench space than a 9cm square and nestled I think I get more on the bench than square pots - however, this only works over a large area, if putting the pots in seed trays, or similar, there is not enough leg-room to gain from offset-layouts (and, indeed, choosing a pot size that have a multiple that exactly fits the tray would be the best policy).

That said, I used to grow in 3" and moved up to 9cm because I though that 3" was too small. Maybe 3" square would do me ... and save space (I'll assume 3" square has the same volume of compost as 9cm round).

The push-button release hand-bulb-planter that I owned (a nice quality one) buckled when confronted with my hard soil :( and its still uncomfortable for my arthritic wrists, but I agree about the long handled ones and making holes / planting through membrane. My clay soil clumps together, so no chance of the plug dropping out of the planter! but I have to fiddle about emptying it.

I was successful last year making all the holes first, laying the membrane, and then planting through it. I use a measuring stick (2" x 1" batton with 4" saw marks on one side, and 6" on the other) and although a bit sceptical that they would line up I found in practice that the holes were spot-on. I did take trouble cutting the Mypex accurately in the first place (and you could cut the planting holes with, say, 10% slack and intentionally bunch up the mypex a bit, along the row, to gather up any slack. Making the holes first means that I can just let the cores eject onto the bed.

My view is that, with Membrane, I am happy with some extra-faff at planting time for the benefit of season long weed-free and reduced irrigation

 

I've checked my pot sizes and the square ones sold as 70mm square are 60 x 60mm at soil fill level, and those I thought were something like 70 or 75mm diameter are 80mm dia. at soil fill level (so probably 90mm 'nominal' size), which explains how I manage to pot up from the square to round ones, and why my square pots (70 x 70mm over rim) take up less space than the round pots (90mm over rim). The size of free round pots I get has obviously increased slightly.



Post above edited to change sizes.

 

There must be a European directive governing measurements of pot sizes then, eh?!!

 

By my calculation a 9cm round pot would have the same compost volume as a 8cm square one. Which begs the quetsion whether I can get more 8cm square pots on the bench than 9cm round ones in a staggered formation ... also assuming that a plant will grow just as well in the same volume of MPC regardless of the shape of the pot ...

Assuming 4cm tall (works for other sizes I have tried)

9cm Round : pi x (4.5cm x 4.5cm) x 4cm = 254ml
8cm Square : 8cm x 8cm x 4cm = 256ml

 

It's probably all the fault of the EU that I can't get the 3" pots any more that were a perfect fit for dropping into the 3" holes made by my bulb planters.

Why doesn't anybody produce a 'bulb planter' type device that makes holes for square pots?

Anyway, I always shift plants from the smaller square to larger round pots so there's more room for more roots, a greater area for the plant above ground to grow and because done at the time of year when densely grown stuff from heated greenhouse/under lights is shifted into more spacious polytunnels as the temperatures increase.

 

You could use round pots you know

I'll get my coat ...

 

I have put plants grown in square pots into round holes made with a bulb planter (but who manages to create a square hole using a trowel?), and backfilled with some of the soil removed by the planter, but it's a lot of faff and messy if planting through Mypex.

Something even worse than pot sizes, is claims for holes made by bulb planters! The calibrations on this one shows it will create a 4" hole if pushed full depth, but it's only max. 3" external diameter so that's a load of nonsense.

 

I put a "drizzling" of Vermiculite over my seeds (instead of compost). That seems to solve the algae-muck growing problem - I think Vermiculite is slightly antiseptic or something like that. Its very light (weight) so seeds have no problem pushing through it, and with my "save, microwave, reuse" policy then over time I get more moisture retention from the accumulated / incorporated vermiculite.

But that calibration is for depth, no? For planting bulbs mate , not strictly intended for putting square pots in round holes But IWKYM

 

I always wondered why they were called bulb planters.

 

I thought it was because it is easier to say than "I'll get my pot-planter-outer from the shed"