The Breathing Pot
by Camilo Mora, Asryelle Mora Rollo & Audrey Rollo.

Background: Seedlings that reach certain characteristics by the time they leave the nursery may have much higher chances to survive. Some of these ideal characteristics include:

1. Seedlings do not have root bounding and pigtail roots. Root bounding occurs when the apical roots of a seedling hit the wall of its container/pot. Pigtail is the same effect but when the root cap or tip reaches the bottom of the pot. In its effort to expand, the root grows in different directions to avoid the pot's wall. A typical characteristic of this effect is a radicular system that looks like “scramble spaghetti”. Unfortunately, after planting, such a seedling will struggle to maximize the volume of soil over which it captures water and nutrients. Additionally, such curvatures in the roots generate weak support to the tree, making it vulnerable to falling even if it manages to grow well.

Example of root bounding.

2. Roots are not stressed by waterlogging or so-call perched water table. If the soil does not drain well, the root system is constantly submerged in water. This makes the seedling prone to disease and causes poor soil oxygenation, which reduces nutrient intake. Some species of trees really hate their “feed wet”. This effect is very common and rarely appreciated because the use of traditional black plastic containers prevents seeing how the water stagnates in the soil.

The physics of water in soil are very interesting. When you put water in a pot, there are three forces at play. On one end, you have gravity pulling the water down. On the other end, you have cohesion between the water and the soil “sticking” water to the soil, and capillarity which pull the water up. Where those three forces even up, the water stabilizes or gets “perched”. This effect is aggravated if you add water frequently.

Example of perched water table.

3. Seedlings are tall. This allows seedlings to escape aboveground competition with weeds after planting.

4. Seedlings have deep roots. This provides a couple benefits to the tree. First, it reduces root competition with weeds. Second, it allows the seedling to tap into deeper water faster.

5. The pots used should reduce planting stress. Most plastic pots require taking the seedling out of the pot, which causes major stress to the root system. This stress to the tree alone can kill your seedling, being one of the major limitations of planting trees with volunteers that lack experience.

The solution to all those problems above is the use of “breathable” pots.

Example of native Hawaiian trees in "breathable" non-woven bags.

Trees really love growing in these bags; they get a lot of soil oxygen, the roots get air pruned (avoiding root bounding and pigtail), there is not perched water table, and after planting there is not root stress, as the seedling is planted with the bag!.

Development: The motivation for The Breathing Pot originated after we faced considerable tree mortality when planting trees with volunteers.

Examples of planting events with volunteers

Volunteers offer an incredibly manpower to scale up tree planting. Consider, for instance, that in Oahu we have nearly 1 million people. If we manage to develop a program that engages, say just 10% of that population, each person planting say 10 trees, then we could easily plant 1 million trees at once.

Planting event with 2,000 people, we planted 6,000 trees in 1.5 hours!

Working with volunteers also offers a unique education opportunity for children and their families; an education critically needed for social norms about environmental protection and individual choices that are detrimental to the environment.

Unfortunately, most volunteers lack experience planting trees, and for many, it could be their first time planting a tree. This lack of experience commonly results in considerable tree mortality due to "transplant shock".

Transplant shock is the stresses faced by a recently transplanted tree. It is a biological process that occurs when the plant being installed has not established a root system extensive enough to keep up with the needs of the plant. This effect is obvious with an almost immediate wilting of the plant, which may result on the death of the seedling.

Transplant shock can occur even under the best of circumstances but it is aggravated by the use of plastic pots.

Traditional plastic pots

Removing the seedling from such containers commonly softens the soil causing a major disruption to the root (the roots get naked). This problem happens to even the best of planters, but it is particularly bad with novice tree planters.

As a result, early on in our project, we did have multiple discussions about the use of volunteers to plant trees. Some land owners preferred not to use volunteers, which increased the cost of tree planting, but it was also a lost education opportunity. Some suggested we have the volunteers go through training before planting; the reality, however, is that most people that want to plant trees, do not appreciate a long lecture about planting trees. We found that only about 10% of our volunteers were keen to take training classes in advance.

The alternative was to develop a planting system that avoided the stress to the roots when we planted trees. Ironically, a person that was not keen to the use of volunteers showed me a photograph of a mistake done by a volunteer, who planted the tree with the plastic pot.

Seedling plated by error with its plastic pot

That error gave me the idea that perhaps the solution to this problem was to develop a pot that can be planted with the seedling. That way we will never disrupt the root system. A Google search into that possibility revealed the experiences of several people growing seedlings on carton boxes.

Examples of plants being grown in paper pots

What an idea, no!. You could grow a plant in a carton box, plant it underground without disrupting the roots, and the box will decompose adding even some organic matter.

Of course, for the scale of planting I needed a mass production of these boxes. I found several alternatives:

Prototypes of boxes used as seedling pots

We learned a few things about this idea. Most importantly, DO NOT USE carton boxes for large scale seedling production!. These boxes offer several benefits: they are easy to fill, they can be planted directly in the ground, we found several suppliers that can custom made them at any given size, design and paper type, etc. However, the problems outweighed the benefits.

The first problem was that if the boxes are in contact with each other and they get wet, they stick to each other.

Carton boxes stick with each other when getting wet and if they are in contact

I try several artifacts to separate them, but that resulted in the weight of the soil causing a collapse of the paper box.

I even try to develop a tray:

Wiliwili tree on carton box set in a designed tray

What a nightmare, that was!.

The second problem was cost. The cheapest carton box I found was 15 cents each, and that was just to much, given that pots are just one of many more elements needed for large scale planting.

The test that we did with the carton boxes revealed, however, another problem. The soil we were using was not draining well. By being able to see the soil profile of the carton boxes after they collapsed, it was obvious that the lower part of the soil was flooded, and to make matters worse the soil did have a strong smell of methane.

Worth mentioning that our soil not only already comes with perlite, we added lots more of it to our soil. Perlite is a soil additive that does not take water, so it increases soil drainage.

Basically, failing to drain the soil was creating anoxic conditions in the soil. The problem of lack of oxygen in the soil is that plants need it to intake nutrients, plus it creates prime conditions for diseases. We found this problem of poor drainage was also happening, much worser, in the plastic pots; we just did not notice it, because the black plastic walls prevented of seeing the soil profile.

Hmm, this work with carton boxes, revealed even more problems about seedling pots.

Fortunately, I can across another product called "non-woven seedling bags", which are sold in Ebay and Amazon.

Commercial non-woven seedling bags

I ordered different sizes of them. And they really worked nicely. They could be planted directly into the ground reducing transplant shock, and by them being permeable, the root system was getting lots of oxygen while allowing water to evaporate slowly avoiding the problem of perched water table.

The bags are also very effective at reducing root bounding by maximizing air pruning. Basically, upon contact with air, the roots get is like having a constant haircut. The benefit of this is that the roots are in a constant latent state to shoot straight out of the bags after planting, which will optimize early root development after planting to maximize the volume of soil over which the roots will take nutrients and water.

Note in the images below seedlings of Kou trees grown in a jiffy pot with a dark tray (A) and the same species grown in a breathable bag (B). The use of the jiffy pots results in round bounding (A), while no roots are visible along the walls of the non-woven bags (B). If we open the non-woven bag and remove the soil with running water (C), this exposes the beauty of the roots in breathable bags (D and E), with roots nicely linear downwards and sideways.

Commercial non-woven seedling bags

However, in our early tests we noted that although the plants looked healthy, they were not growing. An obvious problem was that all available bags were too small. So I found the Chinesse company that makes them, and with them I tested several sizes. Ultimately, we decided to use bags that are 3" in width by 12" in height. This allows the trees to develop deep roots, while allowing to growth seedlings that were several feet tall. These gains in size above and below-ground can give the seedling a huge advantage against weeds.

The result: The Breathing Pot: a system that provides lots of soil oxygen, air prunes the roots (avoiding root bounding and pigtail), avoid perched water table, and transplant shock, and are very cheap, just $3 cents each bag.

Three weeks Kou and six weeks breadfruit seedlings in non-woven seedling bags

Experiments for the development of The Breathing Pot were carried out by Asryelle Mora Rollo, Audrey Rollo and Camilo Mora.