Root pruning containers - 15 gallon size

rainygardenJuly 19, 2010

Would those who use hard plastic root pruning containers please comment on their use.

Also, I have the following questions:

Would a tree, for example, such as a Meyer lemon, grow better, or not as well as in a regular container?

How would a soil mix like the gritty 1-1-1, or the 5-1-1 work in these?

Would these mixes wash out through the sides?

Should the sides be lined with fiberglass window screen to keep soil in?

How often would such mixes need to be changed out?

Would the tree still need to be root pruned on a regular basis? If so, how often?

Could I repot from a three gallon immediately into a 15 gallon root pruner?

Root pruning containers do not have bottom drainage. Should one be drilled in the bottom?

My tree is a dwarf Meyer Lemon now in a three gallon in Florida. This 15 gallon root pruner would be the largest size I could ever go, and will be a permanent container. It will sit directly upon a bed of river rock pebbles.

TIA, and sorry for the many questions. My head is spinning! I have done many net searches but could not find the answers.

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I shared one of my concerns regarding root pruning in your other post in the Citrus forum.

For your other questions, I've experimented with two different fabric containers (aka air pruning) but have not used the hard plastic ones. I assume you are referring to the Rootmaker ARPC brand. I've heard they do work well, but are less effective when transferring from a regular pot into a root pruning container, whereas using air pruning pots from seedling are much more effective.

Although I can't answer some of those questions from direct experience, others are more obvious. Like using the gritty mix in these containers requires even more watering and monitoring to avoid the bark becoming hydrophobic (which I experience here, but I'm in CA with very arid conditions). Your humidity in FL will slightly lessen the watering requirement and hydrophobic concern, but certainly not eliminate it during summer. The gritty mix is excellent for citrus, and in spite of my comment above, the roots will thrive even more with the RPC.

Going from 3 gallon to 15 gallon is a bit dangerous for a beginner, but if using the gritty mix it should be fine.

The black color can be troublesome, if in direct sunlight during summer. To be sure, you'd have to monitor soil temps, since the gritty mix is generally cooler than bagged mixes and the added aeration from the RPC also helps.

If you lived in a location where frost was a threat, you have to be doubly careful with the RPC and especially so using the gritty mix in combination. In my experience, the added aeration of the gritty mix keeps the rootball cooler in summer but makes it slightly more prone to freeze damage. This is anecdotal info only, I have no technicals to back this up.

If using gritty, yes use window/insect screen otherwise some will continue to fall out every time the container is handled. Not as necessary for 511.

Eventually (many years from now for your 15g container) you'll need to remove the tree and examine the roots to see if they need root pruning and should snip a few of the longest ones to help 'freshen them up'. ARPC's are not a complete replacement for long-term root care.

Here is a link that might be useful: Other GW thread re: same topic

    Bookmark   July 23, 2010 at 9:19AM
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Thank you cebury for your response for my particular conditions. Good tips. The container I have is the Accelerator. It seems to be a commercial product as this size usually is. That is the reason I have not been able to readily get information. I have a few that were discarded in a dump site. Even though they are grey, I will check the temperature of the soil, especially during summer.

Yes, we do get frost here sometimes. This sub-tropical climate covers a wide range from humid summers with intense heat and rain, and winters that are dry with possible freezing temperatures. I will cover this tree and container when necessary.

Your response was appreciated because the search engine on GW is not adequate. Following their rules still brings hundreds or thousands of responses that make it tedious to get necessary information.

I was particularly glad to get your opinion on the Citrus forum on pruning this particular tree. As I only have one tree, I intend to gather as much information as I can before repotting or pruning.

I am trying to get information from other sources on root pruning containers. If I get any that is pertinent, I will post it here.

    Bookmark   July 24, 2010 at 11:30PM
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You're welcome.

About root pruning containers, it's up to you but I wouldn't sweat trying to research it more. I would give it a shot. Other than what I warned above about using gritty and for RPC's, it doesn't matter too much as any of the soils will do well, if not better, in them. If anything, the RPC will help make the jump from a #5 container to a 15gallon a little easier. The added aeration should make the edge soil dry out a bit faster.

    Bookmark   July 25, 2010 at 8:57AM
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Rainygarden, can you post a pic of the 15 gallon root pruning container? I am trying to make my own pots and would like to see if I can incorporate the root pruning concept

    Bookmark   July 25, 2010 at 10:47AM
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Without trying to discourage you, if your goal is to create a container for the purpose of root pruning (via passive exposure to air), it is not easy. If your goal is to achieve added aeration in the container and hope it provides *some* root pruning behavior, you shouldn't be disappointed. Either way, by all means make your own. It's always cool to see someone design their own and you may even improve existing products.

You may already understand the info below. If so, I apologize if you're offended by the unsolicited advice and my presumptions. But I took the time to share what I learned to also help RainyGarden with her own research (and future lurkers who may read the thread).

In the moderate amount of research I did, I found that even existing RPC product manufacturers had/have trouble nailing down a successful design. This is b/c roots, as with most life, will attempt to avoid undesirable living conditions. The method of passive air RPC's is to allow root growth toward the container edge whereupon exposure to air causes root tip die-back, encouraging root sub-branching behind it. This not only encourages a more fibrous root ball, but attempts to avoid the natural behavior of excessive root elongation and eventual girdling.

Cutting holes and slits into existing containers have proven to not work well (if at all). The roots will turn to avoid the exposure points. As long as there is ample space in the medium, the vast majority will turn or circle back and stay within it before being pruned.

RainyGarden: This is partly why jumping from a 5 gallon to 15 gallon RPC container provides no root pruning benefit until much later in the plant's life. You can help by fanning out all the roots horizontally when re-potting, but the same major limitation will apply. There are other reasons it doesn't work well, but many surround this idea. Ideally where you could invest the time and dollars, you'd incrementally increase RPC size only when a pot-up was necessary, just like a standard container.

I was hopeful for breathable fabric containers, since the roots would be exposed to air on all sides including corners and seams. But my initial experience is proving somewhat discouraging since a root check revealed several roots behaved normally and elongated right down the side of the fabric container! This is not to say fabric containers are not completely ineffective (several roots *were* trapped in the fabric holes successfully and this was just an early checkpoint). I am only sharing this to exemplify how difficult passive air root pruning is (and ultimately why you shouldn't rely on any container for all your root pruning needs).

I am fairly certain the key to ARPC success lies within the method of forcing root exposure long enough to allow die-back to occur. Various innovative methods are required to "trap or trick" the roots, hence manufacturers approach it differently.

Millet, a respected citrus expert (who is around here now and then but contributes at the Citrus Growers Forum) uses one of Rootmaker brands ARPC products and claims their design is effective, but also warns to be most effective the citrus trees should be started in them while young and incrementally up-sized. But I believe one could place existing trees in them if certain steps were taken to to organize roots, trim the longest, and place in the correct sized container (usually smaller than one typically chooses with standard containers). I do not know how Millet defines success when evaluating it, but much like with Tapla/Al, I would give him the benefit of the doubt.

I've only heard a comments from Al in the past about fabric containers, and it wasn't positive. Not sure what his input is on the variety of products out there.

A bit of history reveals a simple early method developed by Whitcomb in the 70s used a simple milk carton with the bottom completely exposed to air but over mesh. Although his research focused on tap roots, the tall slender container still works today to guide all the roots downward and trap in a specific sized mesh. Although tall slender containers for maturing trees have some drawbacks, I've heard it is supposedly becoming standard for ARPC's used in seedling and early growth.

    Bookmark   July 25, 2010 at 8:24PM
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Cebury, I am now trying the pots, transferring herbs from a raised bed, before any attempt with my citrus. I have a large rosemary that is shrub-like which was the first to go in one. In doing so, I discovered that I had two types of root pruning containers. One, with a drainage hole in the bottom, and one that did not.

Here is a very important question: Should I drill drainage holes in the bottom of the containers that do not have them?

There must be a reason for commercial growers to use these. But my guess is that it would not be the best for a tree long term, as root circling could possibly occur at the bottom. It may not matter much for herbs or other plants. My containers do not have contact with the earth. They are placed on a rock pebble bed.

BTW: My pots are 18" wide (tapers down to bottom 13" wide) x 15" high, I was told this was a 15 gallon size.

granberryflowergirl: It would take time to learn how to post pictures. I found a website selling these so that you could see what they looked like.

    Bookmark   July 25, 2010 at 11:16PM
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Thanks for the link Rainy.
Okay, the more I read about these, it seems they are really intended to initially prepare the plant to take off once it is placed in the ground, not for long term container plants. Or at least that is the gist I am getting. I wonder if they have been around long enough for anyone to say whether it is beneficial to use them for long term containers?

    Bookmark   July 26, 2010 at 8:33AM
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granbury: It seems to be a reasonable assumption that these large RPC are used only to grow trees for future ground placement. I also wonder if there is anyone around who has used them for long term. It is usual to put citrus in the ground here. I don't know anyone who grows them in containers.

I am using two now for herbs. The mix falls out in the RPC. Perhaps I added too much perlite. A nursery owner spoke negatively about RPC, saying that the pot drys out too much unless one has a drip irrigation system.

    Bookmark   July 27, 2010 at 12:34AM
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Suzi AKA DesertDance Zone 9b

Huge fan of RPC here! There is never circling, and when you re-pot you won't believe the thousands of roots you see, and the growth you get.

I do use Al's mix formulated for the hot desert heat, and my container grapevines are healthy and tall. It actually rescued a sad little fig that was in-ground.

I hit them all with miracle grow, now and then, and have never heard one complaint!

Good luck to you!

    Bookmark   May 3, 2012 at 11:44AM
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