Q U E S T I O N :

Plant two, same variety, 4 ft. single-stem fig trees, one in a 10 gallon container, the other in a 20 gallon container....same medium, same fertilizer/watering schedules, same culture.  Both trees grow vigorously.  Fast-forward three years....

Which tree will become larger and why?   Does the container size limit potential growth, even if the trees are root-pruned, and planted into new medium every three years, or so?  Will the tree planted in the ten gallon container remain smaller?

I see photos of very large fig trees, with very large diameter trunks, growing in, to my eye, too small containers.  My guess is that these trees were in ground then planted into containers for sale and easy transport.  They look unbalanced.

I can only grow my figs in containers, and I was wondering if trees planted into a very large container has more of a potential to reach a larger size than if planted into a smaller volume of soil?

At what point should the tree be moved into a larger pot.  Surely, as the root system develops and the trunk becomes larger and larger, the bio-mass to potting-medium ratio will just keep diminishing.  Then you will have a bonsai effect, of limiting growth as a function of pot-volume.  I want to avoid this.

Frank

Good question, Frank! No doubt there will be disagreement on the issue, but I am experimenting with this right now (interesting results). My theory is that initially there will be no real difference. Once the smaller-pot tree hits a certain point, the other tree will continue to grow. Needless to say, this is contingent on all other variables being the same. So, bottom line...size matters.

You are right to think that Frank. Even bonsais are raised in large containers to achieve size before they are refined.

One trick that I learned here has worked very well for me is to allow the roots to grow out of the container into the soil every summer. You will see a burst of growth as the trees expand their roots and catch all the fertilizer that has washed into the soil. This allows me to save some cash and use less potting mix, as well as raise and store more trees during the winter because the containers are smaller. It also helps with root pruning, because roughly one third of the roots are removed when they are dug in the fall. The roots in the containers do not get as congested as they would if they were not allowed to grow out into the soil.

Brent, do you do anything to encourage this behavior?  For example, a certain number/size holes, holes in the bottom of the container vs side, partially bury the container, etc?

I can't speak for figs, but I plant a great number of veg plants in black plastic pots and sink them into the ground. This has several advantages - you can enrich the soil in the pot greatly, it's easier to water and fertilize in the tops of the pots (esp when young) and the roots 'follow' where the water drains out into the soil, ...and primarily it is a great gopher deterrent. Roots go through the holes and the plants grow freely.

The one thing I make sure of is that the pots have holes of adequate size in the sides of the bottoms - for my plants that's about an inch square. Some pots have small holes in the bottoms, and those don't work nearly as well. For larger pots (5 gal), I only need to sink the bottoms into the soil a few inches so the holes are covered and the roots can grow out the bottoms. Works extremely well. I assume it would work well for figs too.

I grow my blueberries (ca 50 plants) in 15 to 20 gallon pots half buried, plus mulched too. Their root systems and requirements are different, but it works great.

Fantastic answers, and even better alternatives that span both container, and in-ground culture. 

The basic answer is yes, container size will limit, at some point, the ultimate size of the tree...even hold back potential growth when the container becomes too small.

So I could sink the containers partially into the soil, essentially letting the tree do its thing, but while keeping it contained, so it could be lifted for winter storage.   I would slice away any roots growing outside of the container...sort of like an annual, partial, root-pruning.  This method might work out for me.

Thanks for the help and suggestions.

Frank

You ask
Which tree will become larger and why?   Does the container size limit potential growth, even if the trees are root-pruned, and planted into new medium every three years, or so?  Will the tree planted in the ten gallon container remain smaller?

Canopy and therfore fruit production in 20g will exceed the one in 10g simply because of the root system management.
When one root prunes there fig trees the canopy should also be pruned as well to keep tree in balance with itself in my opinion.

For example one year when i root pruned many of my trees i forgot to trim canopy of one of my favorites hardy chicago in 30g container.
This tree never dropped figs in any season until that one year when i lost almost 50% of them .

Frank,

Be sure to block the hole in the center of the pot (if any) or pulling the plant up will be extra challenging. Good luck!

Martin....
Thanks for this added information.. This is something I did not take into consideration.

Frank

Professional growers use the guideline that potting up woody material before the root/soil mass advances to a state of congestion where the root/soil mass can be lifted from the pot intact is a requirement for best growth. If a plant is left to grow in the same container beyond that point, growth and vitality will both be negatively affected.

Partially burying your pots does 2 things. One, it alleviates some of the stress of tight roots, allowing your tree to grow under less constraint than it would have if roots were confined to the container only. Second, from a hydrological perspective it turns your conventional containers into mini raised beds. There are several advantages in that arrangement, the two most significant being the fact that it employs the earth as a giant wick, which eliminates any perched water in the container, so long as the soil the pot is partially buried in has a reasonable percolation rate (not clay or in a puddle); and it helps moderate the effects of solar (heat) gain on soil temperatures, a significant plus for container growers in the hot months.

I wanted to talk a little about the "growth spurt" that Brent mentioned and frame that in a different perspective. When we see a growth spurt in our plants, it's a signal that they were being limited, and something we did relieved some of the growth constraints imposed by the limiting factor. IOW, what we take to be a growth spurt is actually the tree shrugging off a constraint and returning to something closer to normal growth.

As growers, the best we can achieve for our plants is to get them to grow normally - that is, to their genetic potential. Every plant we own is capable of that because it's in its genetic code - we just have to eliminate the limiting factors and essentially stay out of the plant's way. In the case of letting roots run into the ground, that helps to reduce the negative effects of the root congestion in the container + the other benefits associated with cooler roots and reduced amounts of perched water, and the plant just grows closer to its potential.

Al 

Great to have answers to questions that were not yet asked.  Now I have the completed picture in my mind, and what realistic goals are possible.  The "mini, raised-bed" analogy made this whole question perfectly clear.

Thank-you one and all for again providing useful, and practical solutions to complex problems.

Frank

Al,

I have an area in my yard that I plan on covering with about three inches or more with mulch and placing most of my potted figs on it.

Can they benifit the same way with mulch as you decribed with the soil?

I do notice that the pots that are placed onto the soil or mulch tend to have their roots grow out. But not the same with the pots placed over the concrete patio.

Thanks

Al- You are sharp, it probably was heat stress on the root zone, now that I think about it. The cuttings are also being stressed from recent up-potting and introduction to full sun (where moving them into and out of sun prevents good pot shading), and I mulch over the south side of the containers at the same time I set them in the ground so that makes sense too. I might find a spot that is part shade for them this year and save them all the extra stress. Putting the older ones out earlier is probably a good idea too. Thanks

I think if you have ever seen a tree grow out the bottom of a pot, you know it is capable of more growth and size than if it were confined to the pot.

Rafed - your trees will undoubtedly find it a plus if you bury them in mulch so it covers at least half the container & keep the mulch moist to take advantage of evaporative cooling so the roots stay cool. The roots like soil temps below 70*, which is difficult to do in containers in the summer. The top of the plant tolerates much warmer temps w/o complaint.

This might seem like a technicality, but a tree's capabilities goes to its genetic vigor or potential. Trees are capable of the same amount of growth, no matter if they are planted in the ground or a pot. They almost never grow as well in a pot because of the several limiting factors we usually allow to have an impact when trees are in pots. We simply aren't as good at eliminating root congestion, high soil temperatures, air:water ratios, nutritional issues ...... as mother nature is. If we WERE, trees in pots would grow as well as trees in the ground, because we would be able to eliminate the limitations.

Discussions that isolate and address the main limiting factors can help close the gap between trees in the ground and trees in containers. In a way, it hinges on an understanding of the difference between vigor and vitality. Limiting factors affect a plant's ability to grow to its genetic potential. You might notice my regular use of the term 'vitality' when I write. It is actually a plant's vitality that we can hold sway over, not its vigor. 'Vigor' is constant and represents the plant's potential or capabilities w/o restraints. Mother Nature provides every plant its own, predetermined level of vigor by building it into each plant. Vigor is the genetic potential every plant is encoded with, and its measure is the plant's ability to resist stress and strain. Vitality, in contrast, is variable - a dynamic condition that is the measure of a plant's ability to cope with the hand it's dealt, culturally speaking. A good way to look at the difference between vigor and vitality is to look to genetics for the level of vigor and to things cultural for the plant's vitality. It's up to us to provide the cultural conditions that will ensure our plants' vitality. Vigor and vitality are distinctly different, and a good case could be made that they are unrelated, but there is no need to delve deeper into that point. A plant can be very vigorous and still be dying because of poor vitality. Far more often than not the term 'vigor' or 'vigorous' is misapplied, where in their stead the terms 'vital' or 'vitality' would have been more appropriate. Reduced vitality is what we witness when our plants are growing under stress or strain and in decline - under the effects of limiting factors.

Al

Yeah what Al said.

Martin....

That's funny, but too long a message.  Next time just: "ditto Al".... two words instead of four. : )

Frank

Yeah, what Frank said.

Ditto musillid 

" OttawanZ5

 : )   : )  : )

Eff

This is a very interesting thread as I am shopping for fig containers.  This may be a stupid question but Frank at the beginning of the thread you discussed 10 gallon vs 20 gallon containers.  However, when I got shopping for containers (at least at the box stores) the size is not given in volume.  Instead the diameter and height are provided.  Usually the shape is not a cylinder but a cone in which the pointy end has been truncated i.e. like the classic terra cotta pot shape.  I vaguely remember from math classes many years ago that the formula for calculating the volume of such shapes is complex.  Other than buying the container, filling the holes, and pouring water in it from a 5 gallon bucket, is there another way to know the volume?  The one I am considering is a plastic faux terra cotta pot that is 23.5 inches in diameter at the top.  Thanks!

Steve

Steve,

Here is what I do. The formula for cubic inches =   Diameter/2 (squared) x Height x 3.14

So,
I measure across the top of the container, lets say 19" inside
I measure across the bottom of the container, lets say 10" inside

Add these two values together to make 29, then divide by 2 which will give you an average of 14.5" diameter; then divide that by 2 which is 7.25"
And 7.25 squared (7.25 x 7.25)= 52.6"

I measure the height, lets say 17"
Plug it all in  52.6 x 17 x 3.14= 2,772"

Then google cubic inches to Dry US gallon convertor and select decimal after it gives you the value. (Dry gallon volume is different than fluid gallon)

Which in this case would be a 10.3 gallon pot. Is this exact, no, but it's pretty dang close, and much easier to calculate than it seems. And half the time I doubt a gallon pail or 5 gallon bucket is all that exact either.

To further complicate the discussion the trade also uses "cheater" pots.  An example is that a 1 gallon pot in a "cheater" is actually 3/4 gal MOL  this started as a mean to save on dirt.  In some cases the cheaters are actually closer to a 1/2 gallon.  It does not matter, the plant will determine the size of the pot needed, do not buy a plant/tree based on pot size, trunk caliber is a much better criteria for buyer value.  There are those sellers that are selling pots and dirt as opposed to size of the plant/tree.  When you see a plant in what appears to be too large of a pot, and it is advertised by pot size, you are being had.

Most pots will list the name of the manufacturer on the bottom. Try going to their web site and look up their code and it should list volume.