Choosing the Right Growing Container: Root Pruning Pots Leave a comment

Hydroponic roots filling their container

Have you ever removed a plant from its container and found a white wall of roots circling around the bottom of the pot? This is known as being “rootbound,” and over time it can lead to a decline in the health of your plants. Bonsai artists are accustomed to the dangers of rootbound plants and routinely prune the roots to prevent root circling and maintain fine, hairy feeder roots. But what about the rest of us who want perfectly manicured roots without the hassle?

Technology for Your Roots

 

Enter root pruning containers. Growers now have the option of using pots that will prune the roots automatically. Originally developed for the tree nursery industry, these root pruning containers employ “air pruning” technology. Take the classic Smart Pot for example. These fabric containers are made of a permeable material that allows the roots to grow through the wall of the pot and reach air. Instead of circling and becoming rootbound, the air desiccates or dries the root tip, and just like pruning top growth for a bushier plant, this “air pruned” root system will send out new roots from all the dormant nodes along the root system.

Instead of long tap and anchor roots, you grow more of the fine, hairy feeder roots. This means in the same volume of container size, you will have proportionately more roots. Generally speaking, a root pruning pot allows you to grow a 30% bigger plant than in the same sized plastic pot, or in theory you could use a 30% smaller root pruning container to grow the same sized plants as what you’re used to growing in plastic pots.

Air-Pots come as three pieces: the container wall, the bottom insert, and a blue screw to hold the assembled pot together.

LET’S TALK SHOP

Smart Pots are fabric aeration containers. Air-Pots are novel in that they are made of recycled plastic and come as a flat sheet with grooves and holes for the roots to grow through. Root Routing Pots are like a marriage of the former two; a hard, fixed container shape with grooves and slits for the roots to penetrate.

Smart Pots are the most economical of the options but present a slight disadvantage as the material can accumulate unattractive nutrient salts on the exterior of the fabric making it difficult to clean. Many customers will wash the fabric in their washing machine or toss after use (which we do not recommend). Air-Pots are nice in this regard as you can unscrew the blue plug, lay the pot flat and either scrub or take a power washer to it. This ability to unwrap Air-Pots also allows you to perform seamless transplants as you simply unwrap the wall from around the root ball and transplant into your next container size without any ripping, tugging, or tearing of the delicate roots as can happen with fabric pots. Root Routing Pots are middle-of-the-road in terms of cost. They don’t have the ability to unwrap like Air-Pots, but they hold their shape and are easy to clean and sterilize.

Standard Plastic Nursery Pot
Smart Pot
Air-Pot
Root Routing Pot

PUTTING THE POTS TO THE TEST

Here at Goldleaf, we are no strangers to side-by-side testing. We want to know if and how our products work. To study the effects of root pruning pots versus standard plastic nursery pots, we set up a 4-way test with cherry tomatoes in 5 gallon containers. We followed the same Nectar for the Gods feeding regimen for all four plants. The control plant was placed in a standard plastic Premium Nursery Pot, and we put it up against 3 different styles of root pruning containers: Smart Pot, Air-Pot, and Root Routing Pot.

HYPOTHESIS

Our hypothesis was that all three plants in root pruning containers would exceed the performance of the plastic nursery pot.

LET’S TALK RESULTS

What we observed initially surprised us. Right out the gate, the plant in the regular plastic pot seemed to “veg out” (or grow stalk, stem and leaves) faster than the root pruning pots. However, after about 3 weeks, the plants in root pruning pots caught up and exceeded the growth rates of the plastic pot. Interestingly, after falling behind in the veg stage, the root pruning potted plants were first to flower. When it comes to tomatoes that are not photoperiod dependent (meaning plants that do not require a certain number of day or night hours to fruit and flower), the plants won’t flower until they sense that they are mature and strong enough to physically support the weight and nutritional demand for fruit production. This indicated to us that all three plants in root pruning containers grew stronger and were ready to bear tomatoes earlier.

These test plants were already pushing out their third and fourth flower sets by the time the plastic pot caught up and put out its first flower. About this time, we also noticed that the plant in the plastic pot was exhibiting signs of interveinal chlorosis, or yellowing between the leaf margins, while the three test plants had vibrant green leaves all the way through.

Our test plants and their respective containers, left to right.
6 weeks' progression
Interveinal chlorosis typically results from a deficiency of Nitrogen or trace minerals such as zinc, iron, magnesium, etc.
Typical foliage from root pruned plants. Notice the even and lush green without signs of nutrient deficiency.

ANALYSIS

To explain why the plastic pot initially vegged a bigger plant, we concluded that in the early stages of plant life, while the root pruning pots were causing those plants to divert energy into popping out new root nodes, the plastic pot roots were able to immediately start circling and diving down to the bottom of the container where it remained wetter for longer between waterings.

We attributed the overall vigor of the root pruning pots to the fact that they created more fibrous root systems with increased root surface area and ability to absorb water and nutrients (similar to how the plastic pot was able to garner more water in the initial phases). This must have been the point in time when the root pruning pots really caught up to and exceeded the plastic pot.

CONCLUSION

Our hypothesis was confirmed as the root pruning containers outperformed the traditional plastic pot, though we were surprised at the fact that the plastic pot seemed to grow a larger plant at first. Perhaps had we doubled up on water in the aeration containers (which do dry out quicker between waterings and require a slight adjustment to watering practices), we would have observed all four plants with vigorous veg growth. The plants with pruned roots did yield more tomatoes than the plastic pot upon final harvest.

When watering aeration containers, we recommend first wetting a small area at the base of each plant to allow the water to evenly absorb. (If you water too fast, the water will find the path of least resistance and spill out the sides rather than wick throughout the medium.) Then we recommend going from plant to plant and gradually watering from the center to the edges of the container. The slower, the better; in fact, an automated drip system is ideal for this style of growing.

Click to enlarge below:
Plastic pot: Note the concentration of roots that has grown around the outer edge of the container.
Air-Pot: Observe the concentration of fine, hairy feeder roots throughout the interior of the container volume.
Smart Pot: The fabric seems to grow the finest, hairiest roots, but notice the lack of roots along the bottom.
Root Routing Pot: Notice how the elevated bottom of this container allowed for root growth even along the bottom of the pot.

When we unpotted the rootballs to observe, it was immediately obvious how rootbound the plastic pot had become. We learned that with Smart Pots, it’s advisable to use an elevated saucer so the plant does not sit in the minimal runoff. Since Smart Pots are fabric, they wick up moisture, so by sitting in minimal runoff, the very bottom of the pot did not dry out as evenly as the Air-Pot or Root Routing Pot which are both designed so that the roots in the bottom of the pot are not sitting flat on the ground (in other words, they allow for air flow under the container). We would recommend a product like Square Farmer for Smart Pots. The Root Routing Pot and Air-Pot both had increased root development along the bottom; essentially, they had an extra surface to grow through and be air pruned.

In the end, the Air-Pot seemed to truly yield the finest rootmass, though a properly elevated Smart Pot would have surely allowed an even greater amount of surface area for the air pruning to occur given the millions of microscopic air pockets in the fabric.

Root pruning pots of any sort are a superior choice when it comes to growing containers. Rest assured that by growing your own, you’ll unlock superior nutrition and flavor, but by growing in root pruning containers, you’ll unlock genetic potential.

First tomato set. They don't call them Garden Candy for no reason. These things are yummy!
A typical daily harvest
The same Nectar for the Gods feeding regimen was given to all the test plants.
Here are some more root pics from around the store… Just for fun!
An example of roots' ability to conform to their container. The above rootmass is from hydroponic cucumbers.
Another Air-Pot versus plastic pot side-by-side test on Rainbow Eucalyptus.
The true power of Smart Pots. Above rootball from pepper plants in coco.
All the rootballs from this experiment. Voilà!

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