Can you put a small plant in a big pot? Do you need to always "pot on"? Jason's answer!

Fire · February 2022

We have discussed the question "potting on" many times on the forum in the last few years. Gardeners usually start a small plant / cutting / seedling in a small pot and then pot on into a slightly bigger pot and then slightly larger and so on to its adult size. I was wondering what the reasoning is behind this thinking.

So I have been asking various gardeners why they 'pot on'. I asked Jason of Fraser Valley Rose Farm in the comments of his last video. He has kindly made a new video addressing the question.

I take his answer below to mean that it's sometimes fine to use just one large pot instead of potting on. He flags two main questions with using a large pot from the off: one is compaction of the growing medium over time (losing air in the soil). C-Fibre is very good for keeping stable aeration over years. The second is a potential to overwater a larger pot re the needs of a small plant. I would say that with annuals like petunias or tomatoes, it's very unlikely that you would get problem compaction over a few months while they grow through the spring while the grow towards maturity. Second, if you have a nicely draining compost and drainage holes in your pot, I don't think drowning would be a problem. (Roses or walnut trees would be growing on in a very different medium from annual sunflowers or lobelia). I personally find that often growing a small plant in a bigger pot often leads to a much bigger rootball forming than on in a smaller pot when the plants are the same age.

I can see how these would the problems Jason flags would be hard for growing roses or trees (as Jason does), regarding their medium and wanting to grow optimal shrubs or trees in multiple greenhouses for sale, but I would argue that a few tomatoes or comsos for the garden a one pot solution might be fine.

It would be very interesting to run some trials and see what happens at home. We wouldn't need conjecture for home growing.

https://www.youtube.com/watch?v=9-KFZg53h70

fidgetbones · February 2022

It depends on whether they are growing in a greenhouse or not, or available space. Most of mine goes in smaller pots to save space, then bigger when they fill those pots.

Fire · February 2022

So it's just a space question for you? I find potting on a faddle so would happily grow six cosmos in six big pots outside on the deck in from May. I've done it from seed that way and it seems to be fine - similar to planting directly into a bed. Some people on the forum were arguing that you couldn't start a tomato in a big pot because it would somehow harm the plant.

fidgetbones · February 2022

I'm always desperate for space. We get frosts until June , so dahlias compete with tomatoes , cucumbers and bedding plants.

Plantminded · February 2022

I'd agree with @fidgetbones, space is the main problem for the home gardener. For the supplier, the plants need to be a portable size to sell on to the retailer - their customers often base their decision on which plant size to buy on cost, hence the availability of seeds, plugs, trays, 9cm pots, 1 litre, 2 litre and upwards. What the customer can afford to pay and is willing to pay must be key considerations.

I don't have space to grow from seed and often buy trays or plug plants of annuals, putting one plant per large pot to grow on, causing no root disturbance or transplant shock, as Jason pointed out in the video.

Blue Onion · February 2022

Thanks for that Fire, so interesting! I've noticed the same myself, with the transplant shock slowing down growth. I've switched to far more direct sowing because the plants I start in March indoors and carefully nurture, pot on, and eventually carefully harden off.. are soon passed up within a month of being planted out by the direct sown that I put in when I planted out. So much for successional sowing.

I've taken to sowing some things direct into their final sized indoor pot, like tomatoes and watermelons, to be hardened off in that container then planted out. As I am not sowing a ton of things anymore, I have space for larger pots to sit for the full duration. I use a mix of general all purpose compost and soil from my raised beds, and they do fine for the six weeks or so prior to getting hardened off.

Jenny_Aster · February 2022

Thanks @Fire for the vid, I watched Jason Frazer's vid of his tour of a composting farm, that was really interesting.

What Jason hasn't considered in his vid are growbags, the sort made of non-woven membrane. Using one of these growbags the roots I understand will be aerated, and it would also counteract his theory that the roots of a tiny plant not being so wet like they would in a much bigger pot.

Nanny Beach · February 2022

Seeds don't need much room, surely you wouldn't put a tomato seed in its final pot

I start off with quarter trays in the kitchen window. Swore blind I won't buy many plug plants this year, because of the late frost last year,they were in the conservatory on every window sill plus the dining table. 3 green houses we had were full of overwintering plants,so we bought another green house.

Fire · February 2022

Jenny_Aster said:

What Jason hasn't considered in his vid are growbags.

To be fair, Jason is a kind, curious rosarian and tree grower for the trade, so his videos are focused on those areas. He's not pondering tomatoes.

I seized on a comment that a soil expert made in a previous video:

"[C-Fibre] is so stable that you can put a tiny plant in a large pot rather than potting it up and up and up. So if you have space, you can take a small plant and put it in a larger pot and then just wait - and you eliminate the labour of transplant."

If you are growing 10,000 maples, this is a huge saving. However if you are growing a few cosmos seedlings at home over a few months, soil aeration and stability for root growth, really shouldn't be a problem.

I keep my small cosmos, phlox, sunflowers in pots to start with because slugs would snaffle them all otherwise. They have to be about two foot tall before they can survive in the ground. I don't personally have much space or a greenhouse or window sills so I don't grow a large amount of plants from seed.

Fairygirl · February 2022

I certainly couldn't @Nanny Beach. They [tomatoes] can't even go in the greenhouse till at least May here, so if I was only sowing seed at that stage, there wouldn't be any tomatoes at all until about September. It would be pretty pointless!

As usual, location and circumstances, and the type of plant aren't being taken into consideration here. You can't compare annuals, [seed] with a shrub cutting. Sowing an annual direct isn't the same process as taking a cutting of a woody shrub and growing it on.

Fire · February 2022

There is a really interesting discussion in the video comments section that may be worth exploring. A viewer comments:

I have heard that plant roots grow to seek the edge of the pot first, and then they grow fine feeder roots based on the size of the pot they “sense”. So if you place them in incrementally larger pots, they will grow more roots vs. placing them in a large pot immediately, as you are “tricking” them into thinking that they must grow all their feeder roots densely, before up-potting them. If so, then that is the only reason I see for me to do incremental up-potting as a home gardener.

Jason replies:

The science is clear that a larger pot allows for more photosynthesis and growth right away - the plant quickly "measures" the size of the pot, and regulates its growth to some degree accordingly... In practice, I've seen excellent and dense root development even when smaller plants have established in oversized pots. I have to say, the bigger concern might be with the up-potting method is the chance that the tree or shrub could develop encircled roots or become root bound at one stage or another.

Can you put a small plant in a big pot? Do you need to always "pot on"? Jason's answer!

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