Air Pruning
A year or so ago, I began growing potatoes in a special fabric container. I've enjoyed using my potato bags. It's easy to move them to get more sunlight or more water from the sprinklers. It's also easier to harvest the crop. I used to grow my potatoes in my raised beds, and had to deal with lost, forgotten potatoes appearing, in later years, in spots where new crops had been planted.
Lately I have been noticing ads talking about the ability of these types of bags and other special containers with perforated sides to cause air pruning. What the heck is air pruning? How could it be helpful? Is this just another hype, like upside down tomato pots?
All of us have dealt with the problem of root bound plants. Sometimes they come that way from the store or nursery. Sometimes we've created the problem by not putting our transplants in the correct size pot to start with or failing to move them up to a larger pot as they grow. However, it happens, the result is crowded roots, spiraling crazily around the edge of the container. These poor roots become increasingly ineffective at absorbing water and minerals and the plant suffers.
Sometimes root bound plants can be rescued and severely root pruned and replanted. But wouldn't it be great if it didn't happen in the first place? When root tips hit dry air, they stop growing in that direction and fibrous root growth is stimulated in other parts of the root. This leads to more evenly dispersed roots that are better able to use the water and minerals available. They are also more effective at anchoring the plant to the soil.
Arborists, forestry and nursery specialists have been finding success with this technique showing increased growth, decreased number of root bound plants, and increased stability of plants and trees raised with these air pruning techniques. Studies at several universities have documented the changes. The types of containers vary depending on the size of the soil particles needed to grow the various plants. But they all increase the exposure of roots to dry air.
Now that being said, there are some trade offs. As you might imagine, containers that increase the surface area in contact with air, on the sides and sometimes the bottom, can lead to them being quicker to dry out. This is an important consideration for places that frequently deal with drought.
Personally, I am going to continue growing most of my plants in the ground, raised beds or regular pots. But I will continue to use my grow bags for certain selected items. But for people with limited gardening space, say a patio or balcony, these could really be useful. In addition to the previously mentioned benefits of portability and easier harvests, another benefit is the ability to fold them up for easy storage in the off season. But I am happy to know that as the nursery industry continues to use and expand these techniques, we will be able to look forward to plants and trees that will be able to be transplanted easier and be more stable, and less likely to topple.
Links to Resources used.
https://depts.washington.edu/proppint/Chapters/air-pruning.htm