Placing seedlings in grow boxes

I have some seedlings that are probably close to two years old and I was planning on reporting them this spring in grow boxes. I was recently thinking that I should slip them out of the nursery tiny pot and place them in the grow box. Not disturb the soil in any way but place them in there now. I’m in south Louisiana so winter isn’t upon me in anyway yet. I doubt it will cause any negative issues and I was curious if it would help with going through the winter with more soil mass? Or should I leave well enough alone and just do a full repot in the spring.

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I always take advantage of these repots to spread and trim the roots since you only get a chance to do this once every year or two. I also repot into a box or pot that is not too big much larger than the ones they are in. It looks like some of yours might be in 4" (10cm) pots. I would typically move those into 7" (17 cm) bulb pans or similar with extra large drainage holes. This allows the roots to colonize the entire soil mass in a year or two. You can then move them to a larger pot or box. Once you get a good nebari started, the repot will be less invasive - prune the circling and bottom roots when you move to the next larger pot.

Of course I am a bit obsessive about developing a good nebari on my trees and it slows the thickening. Some tricks I use are to heat a 1" (2.5 cm) copper coupler until it starts to glow in a torch and use it to melt holes in the bottom of plastic pots. You hold with a long handled pliers and make sure to stand up wind since the fumes are nasty. I buy the shallow plastic saucers to put under pots and melt multiple holes in them - the lowest cost way I know to get a 10" (25 cm) diameter by 1.5" (4 cm) deep grow pot (other sizes are available). I also build my own grow boxes and use a 1/8" (3 mm) wire screen for the entire bottom (1/4" - 6 mm in large ones) to get good drainage and air exchange.

Finally, I would put some shape into the trunks now and/or plant then at an angle since they will only become thicker and harder to manipulate.


Great information on this thanks! I built some grow boxes out of cedar fence boards, that I was going to plant them in the spring. They are 12”x8”x3”deep. Do you think that is not the best for the tree development at this time? I’m fairly new to this but am wanting to do what’s best even if it’s not the “fast” way. Not sure if this matters but these seedlings are in a bonsai soil and have been in it since the beginning. I purchased them from someone who grows seedlings for bonsai stock.

In reguards to adding movement to the trunks, Wiring at this point in the year is not advisable correct?

Second hand experience from a guy I know who did run a nursery growing pre-bonsai material in France…

You will get better/faster growth out of the seedlings by placing them in a large nursery pot or grow bag with a lava/compost mix. The limiting factor will be the amount of watering you can provide during hot days… the deeper the pot the less watering is needed in summer.

For small shohin or mame, you want nursery pots around the 2 gallons mark (1.8 to 2.5).
For larger shohins or small regular bonsai, you want nursery pots between the 3 gallons and 15 gallons.
For big trees, you’re looking at 25 gallons and above.

The soil mix to use:

70% lava, 30% good quality horticultural compost (a mix of brown peat or alternative, bark, …). Tony started with a 50% blond peat, 50% lava mix but the watering schedule was getting very complicated in the summer after large trunk chops. When you perform large chops on bonsai for clip and grow, you lose up to 90% of the foliar mass in one go. That means you’re also going to lose roots and evapotranspiration… so you need to drastically reduce watering until the new buds have emerged. You want the water/oxygen balance to severely tip towards oxygen. Blond peat is awesome and all, but once it has fully dried… it’s not coming back.

Posts 178 and 179 are also relevant here:

Basically because of root tropism, the roots will tend to grow in as straight a line as possible until they hit the outer wall of the pot. At that point they will either dive or start circling the pot if they can’t dive. Some feeder roots will grow downwards from the larger roots, you can safely trim them when you repot. When you cut large roots, cut them as close to the trunk as you can, with the cut facing upwards, because the new feeder roots will tend to appear around the cut site.

Posts 95 and 97 show the nebari work:

Remove the tree from the nursery pot, saw vertically just before the point where the root dived (1/2" to 1/4" from the pot wall), comb a bit, find where the nebari is, saw cut just below the nebari, chopstick to remove the soil, cut off the large roots as close to the trunk as you can, repot. The first year, you can treat deciduous seedlings like cuttings if the starting point of the nebari isn’t satisfactory.

EDIT: Once you’ve built the nebari, the trunk and possibly the primary branching… move to a grow box with mineral soil (akadama, pumice, lava, …) appropriate for the type of tree and start working on seconday/tertiary branching.


Great information. Thanks!

I will ask the dumb question on why shouldn’t I place it in 100% akadama soil from the beginning to keep internodes short as I work on development of branching.

I should take some pictures when I get home, but I have some kumquat seedlings that are close to 2 years old now. The ones I put in Akadama are still very small. The one that I put into regular bagged garden soil is much more vigorous right now and quite a bit taller right now. There are potential other factors (like genetics, my watering, etc) but it’s pretty clear that the garden soil ones will be a decent thickness at some point in my lifetime. Just yesterday I transitioned my other seedlings out of akadama back into garden soil.

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I feel like I may have mentioned this before in some fashion in other posts. The standard pumic/lava/akadama mix is to control the growth of specimens. It has a great oxygen/water balance, however, the CEC (cation exchange capacity) is very low… 25-35 ish. The CEC is important because this is what holds on to the nutrition or fertilizer or N-P-K + micronutrients that can be delivered to your plants. Nursery or garden mixes are very high in organics and consequently they have a relatively high CEC 200-300+ as a gross estimate. The nursery/garden mix also retains more water, even in deeper/taller pots. My point is this… if you want to grow your plants in A/P/L then it will take much longer than nursery/garden/organic/partial organic mixes in a container or other enviroment. This is a generalization, of course, as the water/oxygen balance will change over time for all mixes/substrates depending on numerous factors. Watering, temperature, growth of plant, degree of degradation, etc…

In short, I feel the A/P/L mix of whatever proportion(1:1:1, 2:1:1, 3:1:1) is for trees about to enter or currently in refinement. This controls the growth… vigor, internode length, refined ramification over time. Just my 2¢…

Very good information. My question is although faster, do you produce an arguably “better” bonsai using the A/P/L mix?

In the long term A/P/L is what most of my trees will end up in, although I add pine bark at about 15% total volume for moisture retention and it’s CEC. It’s all up to what you need and want out of your soil. I find it hard to source lava and pumice easily in my area, so sometimes it’s akadama and haydite in a 1:1 or 2:1 even 3:1 for my trees that need more moisture. I live in Texas and I found that 1:1:1 to be too dry for some of my trees during the summer. So I change it to suit my needs.

To answer your question more directly, it depends on what I/you want. Growing a maples in central Texas using A/P/L… Too dry… I found that even plain akadama does not hold the nutrition I want for the growth during development phase. I definitely seen my trees grow stronger and faster in mixes with pine bark. I assume its a multitiude of factors such as pH, CEC, moisture.

Ryan is experimenting with compost extract and teas for their effects on soil microbiology. I assume this is also a reason I’ve seen better growth. Maybe when my trees are another 30 years or more older and I want/need more controlled growth I’ll eliminate the composted pine bark. I would argue you could produce great trees with or without pine bark or organic fertilizers.

You want growth, I would consider adding an organic substrate depending on the species depending on their nutrient and moisture necessities.

You need controlled and slower growth all inorganic substrate such as pure Akadama or the 1:1:1 and anything in between may be what you need. Nothing is more annoying than trying to refine a tree that is growing so vigorously that has 1 inch internodes at the tips after repeated prunings.

All that being said you could adjust watering and ferilizing and achieve the same. I’m not a proponent of with holding water, especially, in +100° F which is a norm during summers in Texas.

Experiment and figure out what you need. No one exact soil composition will work for all practitioners or all species of trees in different climates.

Good luck with your bonsai.

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With seedlings like those I put wire onto the trunk and good branches and slip pot them into colanders with pumice as the medium to make fine roots. Similar to process for collected tree but on small scale. The colanders are acquired at the dollar store, and I place each one into another colander with an inch of pumice to extend the column of water and to encourage roots to grow throughout the whole container. I use organic fertilizer and transplant fertilizer to give them a good start. The roots have filled the small colander and I turn the top container in the lower one to root prune and make more ramified roots. Good success with Zelkova and Japanese Red pines, white pines, and junipers. Shaping the seedlings is important at this time to give them movement. watch the stream Nursery stock rock planting for technique to give movement to seedlings or whips. Good luck, learn from others, teach all who are interested, let us know how they turn out! :thinking:

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Thank you! I will give it a try and see how it goes. I’ll definitely let you know in the future!

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