Grow Pot Suggestions

Currently I have only a few trees which I'm simply allowing to grow out for eventual styling. Right now they are all in 1 gallon black plastic nursury pots. Next spring will be time to repot and I plan to move them into wooden grow boxes. Any suggestions on dimensions for these boxes? I was thinking 4"x10"x10". 1 Gallon is 231 cubic inches, so stepping up to 400 cubic inches would leave plenty of room to grow, with out being too big.

The nursury pots I have them in now I fear don't allow for adequet air circulation to the roots, and are too deep. So come repoting time I'll be looking for an alternative. I'd love to plant them in the ground, but my situation doesn't allow for it, so large pots are my only option.

Tree inventory

2 x acer palmatum
2 x ulmus "jaqueline hiller"
2 x Contorted quince
1 x Korean Hornbeam
1 x Crepe Myrtle (urban yamadori)
1 x unknown, likely Forsythia, but has never bloomed

Thoughts?

4"x10"x10" is smaller than most of my growing boxes. I have lots that are 4"x12"x12" and 4"x14"x14" and a few that are larger. It does depend on how large the existing root systems are and how rapid you want growth to be. If they are really small trees you don't want to massively overpot, as the damp soil will remain that way for too long.

These trees have spent two seasons in their current pots, with the exception of the crepe myrtle which was collected this spring. Their root systems have done a pretty good job of colonizing the nursury pots.

Kev,

I'll have to look again at my available space, but I can probably accomodate some larger pots. Maybe I'll got for 4x10x14.

You only want a couple of inches bigger of a box than the existing (trimmed) root mass.


See Brent's Article, "Root growth, avoiding overpotting" at http://www.evergreengardenworks.com/overpot.htm and you can see some plans at http://knowledgeofbonsai.org/articles/pots-slabs-pottery/grow-boxes-and-training-pots



Will

Thanks Will,

I have read both of those articles before. Currently the roots fully occupy a 1 gallon nursury can or 231 cubic inches. So what is the next step up, 2 gallons = 462 cu. in.? I understand that plunking the tree in too large a pot is just as detrimmental as not repotting at all. I would assume that pot geometry also affects the ideal next step. Moving from a tall cylinder to a low rectangle with more soil surface exposed to the air changes the calculation for ideal volume. Or maybe I'm making this overly complicated...

I plan to leave the trees alone for another two seasons after repotting. This will be my first opportunity to inspect the root systems since I moved them from 4 inch pots two years ago. I'll be doing some root pruning to try and build a foundation for good nebari, but not severe. My aim is to maximize their growth rate.

I have until Feb. to figure this all out. Thanks for the suggestions.

Do you know what a capillary fringe is Cordon?

Ciao.....Leonardo

Capillary Fringe...

Let me paint you a picture:

Water collects between the particles of the soil until it forms a water bearing unit (if you were to stick a shovel in the soil would leak water.) Depending on the amount of rain received and the composition of the subsurface soil, this water table can be above the ground surface (pond or puddle) or below the ground surface (bgs). If bgs, it can be inches, feet, yards or miles bgs.

The capillary fringe is the area just above the water table where the spaces between the soil particles attract the water upward trapping the water in those interstitial spaces without actually holding enough water to be saturated. The amount of water heald in the capillary fringe decreases as the distance from the water table increases.

See photo:



In well drained bonsai soil there really is no water table because all the excess water drains out the bottom. A certain amount of water is absorbed by the clay in the mix and a certain amount is trapped between the grains of sand or grit. Technically it would not qualify as capillary fringe, but the science behind it is the same. As you water your plants from the top, water is absorbed by the clay and organic material and some is trapped with the rest running through.

The capillary action is what allows the soil to hold water between the particles until it dries out or is pulled out by the roots.

Capillary Action:



Surfactants in soil:

A sure fire way to kill your capillary action is to treat your soil with insecticidal soaps and afterwards not water the plants wel enough to remove the residual soap. Soap release the surface tension between the water and the soil particles and allows more water to drain out than would normally.

Found this article.

Surfactants in the Greenhouse


Jay

Jay,

Thanks for the illustrations, however I don't see how exactly capillary fringe relates to my question. The soild I use is a based on Brent's soil at Evergreen Garden Works, but my recipe is this 8 parts orchid bark, 8 parts pumice, 2 parts peat. Though I think I'll reduce that to 1 part peat for this next repotting.

Anyway, I understand how capillary action works to hold moisture in soil, and for plants to draw water out of the soil, but I'm curious as to what the "next step" in volume would be for this repot. I assume with more surface area exposed to air, that soil in the pots I am to build would dry out more quickly. How large should I make these pots? Does 4x10x14 sound too big?

Sorry, I was answering the question of what capillary fringe is.

At my best recollection, you should plan ahead for the repotting so that the grow boxes are prepared in advance and only an inch or two bigger horizontally than the root mass after root pruning and the depth should be about the same. However, You do not want to prune the root mass to short (depth wise) at one time. This may take a few transplantings to get right. When root pruning, I believe the rule of thumb is to not reduce the depth of your rootball by more than a third at any one time. So plan your grow boxes to be just an unch or so taller and wider than your after pruning root mass. Keeping your soil mix as a well drainable bonsai mix will help prevent excessive water retention and as the water pulls its way through the soil and out the bottom, the sucking action of the draining soil will provide ample gaseous exchange.

JAy

Here is the point most people overlook. Any soil, soilless, you name it, no matter where it comes from, no matter what it is made of, no matter how much it is sifted will hold water at the bottom of a container. This capillary fringe occurs in any pot with soil or some type of substrate in it. Capillary pull and attraction is greater than gravity force at the bottom of a container.

Ciao....Leonardo

Leonardo,

We call that a perched water table here and this effect can be minimized greatly by using uniform soil particles and greater drainage areas. It is not really a problem with bonsai with modern substrates and containers.


In example, with uniform particle size, you'll never see a perched water table in this....

The water table and a perched water table are technically 2 diffeent things. Kind of hard to display, so I found a picture.

Will Heath wrote:Leonardo,

We call that a perched water table here and this effect can be minimized greatly by using uniform soil particles and greater drainage areas. It is not really a problem with bonsai with modern substrates and containers.


In example, with uniform particle size, you'll never see a perched water table in this....

You will see a capillary fringe. Lets don't add too may terms to the mix here. Perched water table is a different animal. The screen bottom has no effect on capillary water attraction within particles nor does particle size. This type of information is what confuses people trying to learn the science of soils.

Ciao.....Leonardo

I'm not sure what you are observing in a bonsai pot is capillary fringe. CF is the upward effect of interstitial pressure on a water table. Interstitial pressure is the ability of water to cling to the particles in the soil or potting mix and the surface tension that keeps that water there.

When you water your trees, the water coats the inorganic particles, absorbs into the organic particles and some is locked into interstitial spaces. All excess water is lost to gravity.

Now, if you water from the tray, by filling a tray with ater sufficient to connect with the bottom of the mix, you will capillary movement upward. As in water table that is recharged from the bottom via springs, rivers etc. Even if there is no water percolating from above you will have a capillary fringe.

I think we need an engineer in fluid mechanics to step in on this one!

Jay

I think there is a disconnect in the comparison of a potted plant to the open ground with a water table.

Leonardo,

You are correct, capillary action is stronger than gravity and a capillary fringe would form anywhere water stops decending in the soil column. But Will is also correct particle surface area (could also be termed size) and the surface make up do affect how much water is retained. One cup of crushed granite would retain more water than an equal vloume of granite gravel. But this discussion is not really answering the original question.

Jay,

thanks for the advice. Perhaps I'll go with smaller pots, since my trees are not very large yet, likely 4x10x10.

Jay Gaydosh wrote:I'm not sure what you are observing in a bonsai pot is capillary fringe. CF is the upward effect of interstitial pressure on a water table. Interstitial pressure is the ability of water to cling to the particles in the soil or potting mix and the surface tension that keeps that water there.

When you water your trees, the water coats the inorganic particles, absorbs into the organic particles and some is locked into interstitial spaces. All excess water is lost to gravity.

Now, if you water from the tray, by filling a tray with ater sufficient to connect with the bottom of the mix, you will capillary movement upward. As in water table that is recharged from the bottom via springs, rivers etc. Even if there is no water percolating from above you will have a capillary fringe.

I think we need an engineer in fluid mechanics to step in on this one!

Jay

For now lets forget about water tables, perched water and the like that has to do with in ground forces. This can confuse. Lets talk about a container with material in it and what happens when water is added. That simple. We need to keep it simple because there is a phenomenon that happens within the material that must be understood to move forward.

Ciao......Leonardo

Cordon wrote:Currently I have only a few trees which I'm simply allowing to grow out for eventual styling. Right now they are all in 1 gallon black plastic nursury pots. Next spring will be time to repot and I plan to move them into wooden grow boxes. Any suggestions on dimensions for these boxes? I was thinking 4"x10"x10". 1 Gallon is 231 cubic inches, so stepping up to 400 cubic inches would leave plenty of room to grow, with out being too big.

The nursury pots I have them in now I fear don't allow for adequet air circulation to the roots, and are too deep. So come repoting time I'll be looking for an alternative. I'd love to plant them in the ground, but my situation doesn't allow for it, so large pots are my only option.

Tree inventory

2 x acer palmatum
2 x ulmus "jaqueline hiller"
2 x Contorted quince
1 x Korean Hornbeam
1 x Crepe Myrtle (urban yamadori)
1 x unknown, likely Forsythia, but has never bloomed

Thoughts?

Back to the original question so we don't lost here. The size of box, side to side and depth of pot can be better calculated if you have a basic understanding of soil science. The first thing to consider is the type soil you are going to use so you have an idea of pore size. This will help one understand the relative capillary fringe zone you will expect to have in the container. I always do a test prior to planting so I have a better understanding. This saturated zone found at the bottom is very important to plan for and can be the measure of success in the growth of a healthy root system.

Ciao........Leonard