How to Gain the Best Growth on Trees in Development

Greetings Bonsai Community!
I’m new here and this is my first post (to a topic, which is pretty old but where is always something to be tried/adapted):
Anyone willing to share your experience on growing conditions for trees in development, particularly on what substrates, containers and fertilizers to use to gain the best growth on the trees? Also, I’d love to hear opinions on growing such trees in field versus in containers. I have a mixture of conifers, deciduous and broadleaf evergreens, most of them after or being ready for their initial wiring/bending. I’m on the East Coast, zone 8a. Any input is greatly appreciated. Thank you all in advance, Stan


Take a listen to the asymmetry podcast with the telperion farms guys, I think they had a pretty good reputation for growing some of the best, if not, THE best, field grown stock in NA. But here are a few points to get the ball rolling:

  • Potential development is quicker in the ground than in a pot for a number of reasons including nutrient availability, water & temperature buffering

  • You would typically use a more organic substrate in the field, Telperion I think used a combo of pine bark, pumice and composted manure

  • Containers that air prune and promote root bifurcation can aid in development of a healthy root mass that is amenable to a bonsai pot. These include: Anderson flats, colanders, non woven grow bags and root maker pots. Having said that, a nursery container is a good option too, they are tall giving you a larger gravity column, they keep roots warm and moist and can be cut/perforated/thrown in the trash without having to worry too much about cost.


Hi Stan, welcome to the family. The first things you need to consider are how much land you have for growing and the environmental conditions ie hours of sunlight (are there any fully shaded spots etc) and what sort of soil you have.
Then decide how many and the finished size of the trees you want to have. Next will be the types of tree which will dictate to a certain extent the area required.
As Richard states there are a number of different ways you can grow for development, some better than others. I have a few in the ground - junipers, pines, escallonias, cotoneasters and maple. Non of which are root restricted in any way.
I have lots in airpots (this is a highly productive method for development), plant pots (nursery containers) and a few in seed trays.
I think it’s a case of experimenting with a few and coupled with your environment see which works the best for you.
No matter which method you use, a slow growing tree will only grow slowly but a fast growing tree can be sped up quite considerably.


Donguri, thanks for your time and overview of possibilities. Even though I have experience with growing many various types of plants, except of fruit trees (obviously grown for a different purpose), I have only limited experience with growing other trees, particularly with intention to develop them into bonsai eventually = I need to search on some new-to-me things you’ve mentioned before further discussion about them.
Until then: I do plan to grow (at least to try) some of my trees in my back yard. However, because of not unlimited space but also because some of my trees are dwarf/miniature varieties, I intend to grow those in containers. Would you do the same? If so, what substrate in general would you use for that?

Hi Keith and thank you for sharing what you do to reach the same goal. I plan to use my back yard - a decent but not unlimited size. It has roughly half day of full sun, sandy soil, our summers which can be pretty hot and humid but also our growing season which is quite long - I plan to put there larger, faster growing trees, similar to those you have in the ground. Question: Do you somehow improve/substitute soil for your trees in the ground?
Then I have also some dwarf/miniature trees… If I can ask, how would you suggest to get the best of their (slower) growing potential? What substrate would you use? I’m not familiar with airpots yet - could you send me pics or links to those you use and point to ones giving you best results? Fully agreed it’ll need some experimenting but don’t we all do that more or less? :slightly_smiling_face: Again, thanks a lot.

Hi Stan, this is the link to airpots in the USA
Because my ground is thick clay I dig in plenty of compost (peat moss I think you call it) and grit. I usually do that two years in a row prior to planting and at each time when root pruning. This breaks down the clay and allows for better drainage and aeration. It also allows for better water retention rather than being water logged. It also means I generally don’t have to water unless we have a prolonged dry spell. Because you have hotter more humid weather you could use compost mixed directly with your sandy soil. The humidity would help water retention while the compost gives the tree an organic substrate to grow in. You should see rapid growth from the faster ones. Things like coastal redwoods, Japanese larch, maples all grow well in the ground.
My preference for growing in pots is 50/50 compost and grit (quartzite). You could use chipped pine bark to replace the grit and many nurseries use that instead. You do have to repot at least every two years as the compost loses all it’s structure and becomes almost fluid.
You could try growing your dwarf varieties in a raised bed. Whilst they are generally slow growers they may well put on more structure far quicker this way. In a pot they may appear not to be growing at all.
If you only get half full sun it would be worth considering yews for the more shaded areas as they grow just as well in sun or shade.
For growing in airpots i use equal amounts of coir and compost with 10 -15% of grit.
But as with all things it is trial and error to suit your garden and weather which if anything like ours is extremely changeable.
When growing in the ground you will want to root prune periodically if you let them run free as I do. Every two to three years cut back the roots using a very sharp spade about 18inch from the trunk. You can if you wish rotate the tree at this time if growth has bee a little uneven.

1 Like

I would grow in the ground where I can but if you have limited space this may of course necessitate using a container. Like I said, pots that are designed to air prune roots eg. airpots are really good at developing nice fine roots which makes things a lot easier when it comes time to get them into a bonsai pot. I’m currently using felt grow bags that are above ground but will place the bags in ground once my garden is completed (currently under construction). There is another in-between method I have seen people use which is to keep their containerized trees in a raised garden bed or on weed mat and just mulch over the top with a composted bark. not too sure how well this works, never tried it myself.

as for substrate, I am using roughly a 3:2:1 ratio of composted bark fines, pumice and sheep manure, respectively. I like to play mad scientist but if you have no appetite for making up your own substrate I would just use a high quality potting mix and maybe add in a bit more pumice. Fertilise heavily (according to the product label) and watch them grow :slight_smile:

1 Like

I have been using a mix of grit (pumice and/or diatomaceous earth (floor dry) and native soil for my grow bags that are in the ground). The native soil is probably a good substrate on it won due to the previous use of the land (orchard) and my augmentation with a bark/manure mix when we moved in 20 years ago. I like the addition of of the 1 - 6 mm grit to make it easier to take the root ball apart when it is time to pot into a container.

I also grow trees on in boxes with a 3 mm mesh in the bottom. I use a mix of 40% bark (3 - 9 mm), 40% pumice (3 - 9 mm), and 20% bark and/or bonsai soil fines in the 1 - 3 mm range. Seems to work quite well, but I have only been using this combination of a couple year.

In summary, my thoughts are - fairly coarse so the roots can be teased apart (I find this to be very important), a fair bit of organic to hold and release fertilizer so you can fertilize heavily (I am most organic), an relatively inexpensive.

1 Like

Great, I appreciate. But I also need a clarification: By “growth in the ground”, do you mean planted without any barriers so roots can grow where/as they want to or planted in something (grow bags for example), which would contain roots in? Also, correct me if I’m wrong, but if you eventually place your grow bags into the ground, there will be no further air pruning - is growth in the ground more important than the air pruning? Thanks again.

Thank you, Marty, I appreciate your thoughts. Some questions: Do you experience any difference in the growth using grow bags and boxes (correct me if I’m wrong but I assume you mean wooden boxes, where in oppose to grow bags is no aeration through their side walls)? Do you choose between using a grow bag or a box based on species, size and/or style of the tree you work on at that time or you simply use what you have available? Also, would you mind to share what (organic) fertilizer you use? Thanks again.

Thanks much Keith. Yes, I’ve got a yew and some other less light demanding trees, which are/will be in the shadier spots of my yard. The airpots look good except of their prices… I’ve seen some cheaper alternatives on youtube - would you know by a chance about a comparison of results achieved by using airpots and regular plastic pots with perforated sides and bottoms? Based on what do you choose if you grow a tree in the ground or in the airpot?
Regarding the root pruning and potential rotation of the tree you’ve mentioned - no problem with vertically grown roots (not pruned by the spade I guess)? Thanks again.

My boxes have wood sides and mesh bottom. Traditionally a 6 mm mesh, but I have switched to 3 mm in the past couple of years to accommodate a soil mix with some smaller particles. Growth in the ground is faster than in the boxes, but the boxes allow for a little better control of the roots and to move the trees into the cold greenhouse. I have only been using the bags for a couple of years and it looks like the growth in the bags is slower than in the ground on top of a tile. However, I am hoping that the roots will be much better contained close to the trunk. I plan to lift a couple next year and check. I have also switched my media in the boxes from a coarse bonsai mix (6 - 12 mm and light on akadama) to slightly finer (3 - 9 mm) mix of pine bark and pumice. I anticipate that this will increase the growth rate in the boxes as well. I also grow maples in the shallow plastic drip trays for under pots with large drainage holes and that produces good growth and a good nebari. I am transitioning those to similar sized (20 - 30 cm by 5 cm deep) boxes as the trays crack and otherwise start to fail.


There is a bunch of good ideas here, especially in combination with practices @Donguri and @Keith-in-UK have mentioned. Thank you for sharing. Would be good to hear how your root management check went after conducted. Do you have your boxes made with a gap underneath of the mesh so there is no or only minimal rooting to the ground under, or rooting through the mesh doesn’t bother you much? Sorry about my delayed response - busier than I expected at these days.

There is a short gap (1-2 cm) between the mesh and the bottom of the narrow slats that support the boxes. Most of them are on benches, but even those on the ground show minimal root growth through the mesh.

1 Like

Yip I mean grown in a grow bag, in the ground. while you don’t get the air pruning effect, the bag contains the roots so that it is still easier to pot them up into a bonsai pot when it comes time to do so, but I will most likely be moving all of my ground grown stuff into a wooden grow box before going into a bonsai container.

1 Like

With the ones in the ground I dig completely around and underneath the tree to prune all the roots. Then I usually rotate 180 deg and place a bit of fresh compost/grit in the hole and plant in back in the ground again.
With the airpots it’s easy to repot directly into a bonsai pot within the right size scale. I have a number of Monterey Cypress in 9 ltr (and 1 in 20 ltr) airpots so I would prune the tree at some stage, then either repot into a smaller airpot or into an ordinary nursery pot for a year before transitioning to a larger than required bonsai pot. Then I work downwards until I get to a finished pot and tree.
Next year I aim to experiment with both home made compost and peat free compost. The peat bogs are needed to capture carbon so I heard on the radio today.

1 Like

One thing I forgot to mention is airpots were designed for the horticultural trade specifically to promote root growth prior to planting a tree in the ground. This helps it to grow rapidly and so become established faster. They have even used them to replant the forests around the Congo.
I have yet to experiment with this, it may be interesting to try.

In a pot (for those who don’t have room to grow something in the ground), I’ve also found more success using a soil mix that has some organic material. I use a mix of perlite with a cedar mulch. Other options could be pumice and pine bark mulch - whatever’s available to you in your area.

Thanks for clearing it up. Just still curious - what’s the stage of trees you plant into the grow bags? Do you start also from seedlings/cuttings? Would be nice if you share some about the phase as well.

Thanks Keith. Good to know you care about the environment too.

1 Like