Are these going to root into the ground? If so pot size won’t control tree size at all. If strictly limited to a pot then staking will be necessary for all roots. I’d go M26 or smaller.
One of the problems I’ve found with growing trees in containers is J-hooking and circling of roots. This is true even when the containers are only used when the trees are young and then they are transplanted into the field.
I have really taken to root pruning containers. There are a number of techniques used in containers to prune, air pruning, root capture, and root constriction. The concept is that by pruning the tap root quickly when the tree is small, it forces early secondary and tertiary branching. More root tips = more efficient uptake of water and nutrients but over a smaller area. The down side to this technique is that if you plant a tree in the field and get a drought before it is well established and can’t supply supplemental water you will lose the tree faster than a deep tap rooted tree that can reach deeper into the water table. The upside is much faster early growth given moisture and nutrients are available.
The technique uses a series of containers increasing in size as the tree grows. I typically keep trees in containers for 2 growing seasons or less before planting them in the field, so I don’t have experience with using them permanently. I’ve been using a 50/50 mix of Promix BX and mini-pine bark nuggets. With these air pruning pots and this mix, they are very well drained.
I will share one experience that may be of interest. I’ve been working with some TIgertooth Jujube trees. They have been in the field for about 5 years and have not yet fruited (hopefully this year). A couple years ago, I took some root cuttings (grown on their on roots, not grafted) and started some more trees in air pruning containers. It takes a long time for Jujube root cuttings to produce top growth. I started them in December and didn’t get top growth until late May. These same trees produced a half dozen fruits each by that November. I was shocked since the parent trees still have not produced fruit. After discussing the situation with a professor that specializes in Jujube, he concluded that the root containment forced the trees from a vegetative state to a fruiting state very early. He said that if I plant those trees in the field they will likely revert back to a vegetative state for several years.
I have found that these root pruning containers produce a very dense fibrous root system. You can get a lot more root mass in a smaller container supporting more top growth with these.
By the way, the brand I happen to use is Rootmaker. Dr. Whitcomb pioneered these techniques. Regardless of what brand of root pruning container you use, these two short articles of his provide some good insight into the underlying concepts:
I’ve been using Whitcomb bags for over 20 years in my nursery, which is a different use than what you folks are talking about because they are grown to sell. Their point is to allow me to easily dig up and move bearing age fruit trees.
Whitcomb designed 2 types of bags that are quite different. He only has the patent on the white bags that allow a lot more root to escape from the pot than his original black bag design which is made out of what is essentially heavy landscape fabric.
For the purposes described here I use the black bags, for nursery purposes I use the white.
Very interesting. I have not tried any of the in-ground root constriction type bags (knit green). I have tried the white bags they call Roottrapper II. These are some kind of knit fabric inside that traps the root tips in the fabric and a white PVC material on the outside. I have found these retain water much longer than some of the other kinds of rootmaker containers. I have found that they don’t prune large tap roots very well. They work great for fine secondary and tertiary roots. I typically use the 18 cell Express Trays for the initial propagation.
With my application I generally only keep the trees a season or two before planting them at my farm. I like the Rootbuilder II containers verses the bags. The require more frequent watering but that is not an issue for me. The reason I like them is that they are very easy to disassemble when planting and can be reassembled for many reuses by simply replacing the cable ties. I’ve been able to get a few reuses out of the white PVC bags but stapling them back together. This does change the water movement through the container somewhat, but works fairly well for a few reuses, but after a while the bags begin to rip at the staples.
The largest downside I found to the RM containers is the up front cost. I was able to establish a commercial account with them which makes them much more reasonable in volume.
I used the knit green for a while season, 20+ trees in all, all bare root. Had root branching on a almost every one. It’s amazing to pull up one of those trees to find the thick root plastered into the side of the bag and 9+ feeder roots going out from there.
A little more explanation is in order.
My understanding had been - at least in the case of Smart Pots - that when roots hit the side of the container, big roots would not be able to grow through the material (due to the small hole size) and would instead tend to send out a bunch of small roots that would spread through the potting material, improving uptake of water and nutrients from the potting material. I had also been under the impression that some small diameter roots would grow through the side of the pot if the pot were buried (or partially buried) in the ground. In this way, I had figured that for a tree in a Smart Pot, something like 80% or so of its water and nutrients would come from the interior of the pot and maybe 20% or so from the ground surrounding the pot, and this restriction in the volume of material it was drawing energy from would in turn naturally restrict the size.
However, fruitnut commented: “Are these going to root into the ground? If so pot size won’t control tree size at all. If strictly limited to a pot then staking will be necessary for all roots. I’d go M26 or smaller.”
Have I misunderstood?
My thinking had been to have a tree in a Smart Pot (or similar product) and have the Smart Pot buried halfway into the ground. For several reasons - including that we are renting our house, rather than being homeowners - I don’t want trees or other plants (e.g., grape vines) to become a permanent part of the landscape that I can’t remove.
My expectation is that within the next year or two, our circumstances will change such that I can switch to a controlled environment for growing (something similar to fruitnut’s setup). Naturally I would want to be able to move any trees or vines into such a setup. After moving I would still want to restrict their sizes (e.g., no more than about eight feet tall) to keep them easily manageable.
In light of the details added above, any additional information on size control using fabric bags (e.g., Smart Pots, Root Pouches), which fabric bag types would be appropriate for my application, etc. would much be appreciated.
I would think if you buried part of a fabric pot it would pretty much fall apart if you moved it. The ones I use only last 4 years above ground, probably 1 year under.
Drew: Which type of fabric pots do you use?
Anyone: Do other types last longer?
I use root pouches, cheap! Like me! I’m easy! And cheap!
Others may last longer? But for the money these seem the best deal. 4 years you should change soil anyway!
Various pepper plants. I don’t use them for trees, all my trees are in ground. I plan on growing figs in them though and may put a Carmine Jewel in them too. Currently in hard pot, when soil needs replacing I will put in a 30 gallon. Up to 100 gallon pouches available,
Once a tree gets a root into the ground the pot will become pretty much irrelivant in controlling tree size. Sure it might slow it down but not much nor for long. You could resort to root pruning outside the pot. But that would be much easier in a hard plastic pots with holes only around the bottom of the sides. That’s how I’m doing it with figs and grapes in my greenhouse. I got tired of watering so many things everyday so am trying this experiment. And some so I can move them easily next winter.
The original Whitcomb bags, and I don’t even know what they are called because I haven’t ordered any for years, are what you can use for in ground container growing. They will require much less frequent watering than above ground pots with a potting mixture because you use real soil with them, they are in the ground (insulated) and fine roots escape the pot. I’m sure they benefit from capillary pull and mychorizal action as well. Benefits of mychorizal relationships are going to be much, much greater if the fungus is spread out in the soil far beyond the pot, including helping trees get through drought. .
I still have some around and use them for a couple of my figs and a persimmon tree.
The white knitted bags I use now let a lot more root grow outside the bag so they work well in my non-irrigated nursery.
I can’t speak to smart pots because I haven’t used them, but I can speak to root pruning techniques.
Let’s start with a regular plastic pot with smooth sides. When a root encounters an object like the edge of a pot, it tries to avoid it. That means growing in a different direction. The only real options are to circle around the pot or to J-hook. Both are bad scenarios for the plant.
One of the in-ground bags that Rootmaker sells as a green knit fabric. They are designed to be placed in the ground. The material has holes in the bags but the material has limited give. When a root tip hits the bag it avoids the material like any other object (rock etc.) and grows through one of the holes. As the root gets larger, the diameter fills the hole but he material does not stretch. This constricts the root and has a pruning-like effect causing the plant to begin branching upstream.
The Rootmaker above ground bags work differently but have the same affect. When the root hits the edge of the bag, the fabric captures the fine root tip when it is small (large tap roots can still circle, so this type of bag should be used as a secondary or tertiary stage). With the tip of the root captured, it can not turn and circle or J-hook again causing secondary branching upstream.
The Rootmaker above ground plastic containers work differently. They are designed with small protrusions all around the container that direct roots to holes at the end of each protrusion. The bottom of the containers is designed with ridges that direct roots outwardly toward the edge of the container where they enter one of the lower row of protrusions. In this case, once a root grows through a hole, it hits the air. This desiccates the end of the root effectively pruning it.
There is a bit more to the science behind how frequently to transplant and how much larger container to use that is described in the 4-Inch rule link I posted earlier.
FSF, that is not quite the whole story for how my trees grow in the Whitcomb rootmaker bags. Some species like peaches and mulberries send small roots out of the holes but the roots just keep growing until they become very large roots that are seriously weakened at the point they pass through the bag- tissue passed through the holes as a large root but the root snaps when you pop the bag out with a heavy spade.
The spun black poly bags of his first design do a better job of keeping large roots in the bag, but require drip irrigation to get trees to grow well.
As far as the rootmaker design, Whitcomb claims that a lot of carbohydrate is stored in the root directly inside the bag, but I still find my peach trees transplant better when I grow them straight in the soil (light sand) and carefully dig up most of the roots and move them to new sites as bare root trees.
His system is better than balled and burlapped but I think the best system is to move 2-3" caliber trees bare root, planting them the day you dig them up.
I don’t have any experience with the in-ground bags or the broad variety of trees that you have. Most of my experience is with the 18 cell propagation trays and Rootbuilder II above ground plastic containers and some with the PVC coated above ground roottrapper II bags. My experience with growing trees in them is limited to Dunstan and Chinese chestnuts, Jujube, Pawpaw, Allegheny Chinquapin, Persimmon, and I’m just starting to play with crabapple.
Your real world experience with the in-ground bags trumps mine. I looked hard at the green knit In-ground bags for an application but decided to stay above ground. I’m not doing anything commercial. All of mine are just for planting on our farm, primarily for wildlife management.
By the way, here is an example of the Rootbuilder II pots:
These are 250x39 pawpaws started from seed in mid-October in 18 cell Express trays and then transplanted to these 1 gal Rootbuilder II pots. You can see the edge of some 3 gal RB2s to the right of the picture to give folks a feel for size difference. They have some grafted persimmons growing in them but the are off the edge of the picture.
Check out A.M. Leonard.They may have a better deal and today only,there is 15% off if $130 or more is spent.Use code MM15PE. Brady
I’ve used the pots as well, but they used to look a lot different. My only issue with them was they are hard to water with all those holes on the sides.
Sean2280. what is the 511 mix comprise off? I have been using pots ranging from 3-15 gals. I heard that the bigger the container the better but space is an issue for me so I try to keep pots small. This fall I am going to attempt root pruning to so that I do not have to move to a large pot. Has any container grower done this and if so, do the tree bear the following yr. Not that mine does as full sun is also an issue for me. It is challenging growing fruit trees. 2 yrs ago I had asian pears fruitlets but the chipmunk got them. It was a 5 in 1 pear. This yr the graft grew back? not sure if it is the bud graft or from rootstock. There are flowers now but whether I get fruits or not, time will tell. Today I planted several bare rooted trees, I used Foxfarm Lucky Dog for the 1st time and mixed with some old potting soil and their ocean frost blend.
The 5-1-1 mix that I use consists of 5 parts of pine bark mulch (the partially composted stuff, not the chunks) 1 part peat moss, 1 part large coarse perlite, 1 tablespoon of dolomitic lime per gallon, and then Osmocote Plus (not plain, the Plus). Couldn’t be simpler. Doesn’t cost as much as bagged potting mix, and drains pretty darn good. Find it hard to over water. Every now and then I supplement a liquid fertilizer.