I did a controlled test this year Two Same Cultivars from same grower, same 1G pot size. I put them in 2G pots this spring In Early-Late August, I put one in a 15G pot The other one I slip potted in a 3G. The one that was put in a 15G pot has a larger round of new leaves easily 2.5X than the latter. I pulled it up just to see. The root system is larger. A few almost to the depth of the 15G pot Same potting medium I never understood how many seem to advise the 1 pot upsize.....but as long as my drainage is okay and the root system can hold the plant in the potting medium (and or a stake and a rock or 2 to hold the plant down till the root system takes a firmer hold in my fairly airy barky medium), the general consensus of 1 pot upsize doesn't make any sense to me, unless one is using it to control the size of the plant.
I've also been dubious about such advice, so it is very interesting to see your findings to the contrary (and that support what I have always considered to be common sense). There are so many "wives tales" that govern our gardening techniques and less science. Mr Maple has a video on YouTube claiming that putting a JM into a pot that is too large will cause unbalanced root growth, which will be "overwhelming" to the plant. Makes no sense to me but they also have vast experience. Or perhaps they're just perpetuating wives tales. Anyhow, I've always just disregarded any advice in this realm since other considerations have always been more important to me, such as aesthetics (a tiny tree looks silly in a massive pot), what pot I have available at the time, what trees I have that I want to pot up, etc.
I will have to find an older thread I started discussing container upsizing and why the universal advise was to up-pot 1 size. I did make the statement that what is the indifference of planting it in the ground where there is not 1-upsize rule. For me, I do have large 10-25G volume containers and making bark mix is pretty easy. JM's are new to me so for areas that are not afternoon shade, but anywhere from full sun to dappled shade, I am putting these in pots to put them in proposed siting conditions to see how they interact with the sun before I plant them final in the ground. Slightly interesting, but planting smaller 1G seems to be less stressful to sun scorch than 7-15G ones that may have been under a hoop house for it's entire life
One possible concern is that potting into a much larger container can cause soft branch and twig growth that does not harden off sufficiently before winter and is killed by frost, causing potential entry points for nasties such as Pseudomonas bacteria. Obviously YMMV depending on local climate and luck.
What is the difference on large container versus for discussion, taking this 1G and putting into earth dirt where it's unlimited *G* in volume....just short of root completion from adjacent plants, lawn, etc. That's primarily my POV in that regardless of the original pot size, as long as the plant is stable in it's position *larger pot may not root as tight to walls and require a stake + and rock* for a season till it roots in, I don't see any gain on upsizing 1 pot up. The post was to question this sage old advice, as almost everything I read from JM container growers is to up pot 1 size up. Even a video from a professional mail order nurserymen. I dunno. I may be experimenting it all wrong. But the -control sample- I did, like for like , cultivar, potting medium, siting is all the same. The larger pot speaks volumes that disagree with the sage old advice...
Not particularly concerning maples, but a concern I was told years ago re: houseplants was that if potted up to a size too much larger, there was more chance of damage from overwatering, as there would not be enough roots yet to take up the excess water. When planted directly in the ground, water would be able to dissipate. On the other hand, I was also told, regarding jade plants, that if you want them to grow rapidly, put them outside for the summer in a much larger pot, and they would grow to fill the pot, which turned out to be the case. So I think the issue is whether there is a likelihood of repotted plants sitting in soggy soil, and weather, temperature, location, attentiveness of the gardener, type of plant and type of pot might all have some play in the effect of the pot size.
Commerical production operations routinely move plants of all kinds up to much larger containers on a routine basis - it is not cost effective for them to repot in small increments. And not necessary - there is no such thing as "overpotting". Same as when container grown plants are placed in the ground, the involved specimens do not fail because there is suddenly a lot more soil around them.
If you have limited time and LOTS of containerised JM like me, and so it’s unlikely that you have the time to pot-on in smaller increments, I’d go oversized and focus on the components of your potting material /compost to ensure it’s as free draining as possible. I do recognise the concept that @wcutler mentions in terms of root mass not being sufficient to draw all of the water from the peripheral area’s, that makes perfect logical sense but, with a very good free draining growing medium, the risk of stale wet areas are minimised. I think it’s a better bet to have some excess growing space with good potting material than end up with a root bound plant.
Accepting that the excess potting material will lose some of its nutrients before the roots get to it ie the nutrients being washed out
Small pot that hugs roots to large pots as being discussed....I approach it just the same since I tend to have fairly well draining medium so everything just leaches out anyhow when I water I just give it some micro-macros in pellet form and every once in awhile I'll give it some liquid fertz. Slightly interesting but whenever I receive it from the growers, the top of the pots are generally caked with Prills. I get it, it helps them to grow bigger faster....
as long as you have a strong back, use the larger pots as you seem to be determined to go that route regardless of comments being offered. The one important variable is the type of soil medium to ensure good drainage which has been mentioned
I'm not determined but the advocation to upsize one 1 size up seems to be a general common advice doled out, including from the advice of a fairly large mail order JM nurserymen. Has anyone done this same A-B test I have done in post #1 Cause the control test I did shows entirely a different response to the plant. I can see is putting it into a pot to control size (aka, the bonsai effect) But putting it in the larger pot IMO does not negate the growth of the plant--- in this one small test I did, it seems the upsizing it 1 pot does.
save to say, during our nursery years we up potted over 20,000 maples. And still actively looking after a large number of container grown japanese maples on our property and repotting, root pruning etc as needed. Generally our rule of thumb was to always go from a 1 gal to a 2 gal pot. After that we would bump up to a 5 gal pot. After that ( which generally would be 5-6 years after the actual graft), then decide on the final resting home for the tree. Once the roots have really pushed out and filled a 5 gal container then the risk of putting into a really large pot is diminished as far as the root system being over saturated , etc Personally I think it is very important not to go to a large pot until after the root system has successfully developed /filled out. Again there are many who would disagree, but that is personal experience and many years of observing. The only reason I can see a plant going from a 1 gallon pot to a 5 gallon pot in the nursery industry is to suck more $$ out of the unsuspecting buyer.
That's true! Not only house plants but veggies also need more precise watering regime, when up potted into oversized container. Commercial growers are usually more proficient how to water their plants properly, so they can skip intermediate sizes. Potting 1 size up has ability to keep plant growth under control, it's important if the space is limited (like for house plants it usually is) and slower growth rate is preferred. Often limiting the root growth can affect fruiting too - plants who find themselves under vegetative growth restrictions, often start to fruit earlier.
In the realm of a grower (growing for sale), I can see how 1-2-3G or 1-2-5G applies The aim is to market them forsale once the crop is ready And UpPot on the ones that don't sell that season for the following season It saves on space, potting media, will fit tray inserts, etc The OP was more on consumer-owner (non trades) POV
My comments on the way we re pot are all geared to owner grower / collectors, we do not subscribe to any fast grow approaches that many commercial growers try to use. Part of the journey of growing japanese maples includes appreciating their very slow and natural rate of growth right from the initial graft. They have to be the cutest trees out there (imo)
This thread has gone a few different directions. To summarize (as I understand it, and talking only about Japanese maple cultivars): If you are in the business to make money selling trees where space and efficiency matter, you should slowly go from 1g to 2g to 5g as the tree grows. That makes sense. If you are wanting to limit the growth rate of a tree to maintain a compact form or shape, you should slowly go from 1g to 2g to 5g. That makes sense. If you want as much growth as possible you should put it in as big a container as you can reasonably afford the space for, assuming you care for the soil and the tree properly. That should make sense, but we don't all agree on it. The OP's "experiment" is a start, but to be truly scientific about this, we'd need to have many more trees in each group, and to control all of the other variables as tightly as possible, then spend years observing them. I doubt anyone has done this nor likely ever will. Otto, I have respect for what your experience has invariably taught you. Did you ever try going from 1g to 5g, and if so, did you find that the trees were "overwhelmed" and did poorly?
@kines yes, we have tried potting from 1 gallon to 5 gallon way back in the early years to observe and see if there were differences , but we quickly realized there was no difference at all in growth rate compared to a 2 gallon pot. What we did notice however was a more robust and healthy looking cultivator in the 2 gallon pot, also a much better balance of knowing and understanding when the tree needed water. Most important however we realized the root system was developing much nicer in the 2 gallon pot. Our end analysis was that the fibrous root system of the japanese maple was struggling due to excess water not draining from the pot. And also with that in mind our soil mix is extremely porous, and soil mix I believe is by far the most important factor when it comes to growing a japanese maple in a container. I do have a video on my youtube channel explaining our soil mix in detail and how easy it is to make yourself. What many new or first time growers of japanese maples do not understand is that the trees grow slow! Allow them to grow at their natural pace and you will be rewarded with a beautiful mature cultivator. I honestly don't understand the desire of so many gardeners trying to get their japanese maple to grow at an expedited rate that ultimately can harm the tree or really distort the actual size.
I don't have an access to major science databases like my sister has, but even Google finds several research papers about the effect of container size. As it is common for science papers, they refer a lot to other similar studies. https://swfrec.ifas.ufl.edu/docs/pdf/veg-hort/transplant/trans_cs1.pdf https://www.researchgate.net/public...the_effects_of_rooting_volume_on_plant_growth https://academic.oup.com/forestry/article/87/4/482/2756053
Nice reply Otto, thanks. Like I said, I have respect for experience. And I do certainly agree with you regarding how we value size. One of the main reasons I grow Japanese maples is because they are small and slow growing and can be enjoyed for many years in the limited space I have!
@Sulev I suppose a scientific study could be helpful to some. It would be nice if there was a study that was truly specific to japanese maples. My bible was always, and still is J.D. Vertrees Japanese maples. And of course often missed by many, are the insights of growers who have spent there lives growing the japanese maples in containers with no controlled environment.
@Otto Bjornson What would be the success metrics for scientifically comparing JM-s in different sized containers? Is the tallest tree the winner?
@Sulev We found a much robust look to the trees potted in the 2 gallon rather then the 5 gallon, nothing really to do with the height of a cultivator at all as there are so many different growth rates in the different specimens. To get height in a young upright japanese maple is very simple, just over fertilize which so many growers tend to do. Of course that comes with a down side as it dramatically changes the natural growth cycle of the tree. And my opinions come from a growers perspective, not scientific research.
Sulev makes a good point about the need to define an outcome for this putative study, and doing so might not be so straightforward. The OP defined it as more leaves and a larger root system. I am enjoying this discussion, having spent 25 years in my prior career as a clinical researcher, designing and performing studies to answer questions that guide the use of medical therapies and advance the practice of medicine. I would enjoy doing this "up-pot study", but to do so correctly would require far more resources than I would expect anyone to be willing to commit, including myself. One thing my experience taught me (other than how challenging a proper study can be to design and implement) is that the results of a study can sometimes absolutely defy what you thought you knew from years of practice and experience. It's a good thing my enjoyment of these beautiful products of horticulture has nothing to do with the answer to this question, and that I'm completely OK not knowing.
From our experience , a tree in 2 gallon container will absorb the water more quickly then a 5 gallon container. The root system in the 2 gallon will push out and fill out at a faster pace then the 5 gallon container. And to put it in context, the root system in the 2 gallon pot pushes out in a way that compliments the container grown root structure which is really comprised of more fibrous roots rather then more structural supporting larger roots. It is an ideal approach to container growing in the long term as the roots adapt to the container environment. The excess moisture in a 5 gallon container did slow the root growth slightly as there is more moisture available and no need for the root system to push out as quickly. Again a personal observation and that is why we always thought the 2 gallon tree just had a more robust look with a denser and fuller root system. With the 5 gallon container the root system did not grow nearly as fast due to the excess moisture readily available in the larger pot not being absorbed. The trees were always watered at the same time every day during the entire growing season. We stopped repotting 1 gallon to 5 gallon pots after that season and always moved first to a 2 gallon pot. This is just personal observation from our nursery years.