Air Pruning Basics: How It Works and Why It Matters

Air pruning is a technique used in gardening and farming to eliminate the ability of a plant’s roots to circle the pot and become rootbound, leading to healthier, more resilient plants. While the technology has been around for decades, its availability to casual growers and commercial farmers recently widened after the original tray’s 2016 patent expiration, flooding the market with various options.

We created our take on the design, which became publicly available after multiple design iterations, exhaustive testing, and a few manufacturing partners. Bootstrap Farmer currently offers air-pruning fabric grow bags in various sizes, 4-cell plugs, 6-cell plugs, and 72-cell seed-starting trays.

Plants grown in air-pruning pots and trays experience less stress, more productivity, and advanced root systems, leading to long, healthy lives. If you’re behind on your transplanting, don’t worry; air pruning trays have you covered. Here, we’ll explain how air pruning trays and containers work and why you should use them.  

What Is Air Pruning?

Traditional pruning removes overgrown, diseased, low-hanging, and dead growth to promote health, decrease disease risk, encourage new development, and increase productivity. Air or root pruning is a natural way to prune roots. When they hit the air, they die back due to lack of moisture and humidity, encouraging the plant to produce new ones leading to vitality and fruitfulness. 

This idea for air pruning was born by a Dutch man named Aart Van Wingerden, who came to America in 1948. He noticed the roots would curl up and strangle the plant in traditional pots and was searching for a way to grow healthy seedlings the way they grew in soil blocks, without the tedious nature of soil blocking. Among other crucial items we use today in greenhouses and fields across the globe, Van Wingerden invented and patented the first air pruning tray. Read The History of The Air Prune Tray to learn more about how our air-pruning trays came to be. 

In traditional containers, roots naturally grow to the bottom until they hit the plastic bottom. Then, because there isn’t anywhere else to go, they begin to circle themselves at the bottom, creating a thick mat of bent, fibrous roots unable to breathe. Sometimes, these roots choke out the plant, leading to its death. Other times, growth stunts upon transplant, productivity is low, and disease is more likely. 

Air Pruning Results from Soil Blocking

If you’ve ever used soil blocking for seed-starting, you know the benefits and the rigorous process. If not, check out our article, Soil Blocking 101, to learn more. Soil blocks aren’t contained by an impermeable boundary, allowing roots to breathe and preventing them from encasing themselves and binding up.

Air pruning trays, pots, and containers are more realistic for large-scale growers because they’re less time-consuming to produce and easier to move around. Air pruning containers draw feeder roots to holes or slits that lead to the outside, where they dry up and die when they hit the air. Root death encourages the plant to produce new ones, and they’ll continue to do the same, leading to a healthy, productive plant. 

Here, we explore the pros and cons of traditional plastic pots, soil-blocking, and air-pruning containers. 

Pros and Cons of Air Pruning 

The Science Behind Air Pruning

Air exposure will kill a live root after just a few hours or days. Death sends a hormonal signal back to the plant, indicating that it needs to produce more, which it does. The roots will continue to grow laterally and every which way, preventing root circling and becoming root-bound, mangled, or girdled. The abundance of fresh, new roots provides an increased surface area by which the plant uptakes water and nutrients before and after transplant. Plants would not properly grow, uptake nutrients, absorb water, resist disease, or produce energy without a constant oxygen supply. 

Pro tip: Using air prune containers with young trees or bare-root strawberries will further decrease the likelihood they will experience transplant shock or fail to venture out into the native soil, even clayey soil. We recommend growers add organic matter and amendments like vermiculite and coco coir to improve their soil’s texture before transplanting. Top 10 Best Fruit Trees for Clay Soil offers helpful tips and solutions for growers with native clay soil. 

Key Features of Air Pruning Containers

Air pruning containers are made of porous materials or have evenly spaced holes on the exterior. Cloth bags and collapsible designs are easy to wash and store between uses. Breathability, air circulation, and soil aeration are high, allowing plenty of oxygen to reach the roots. Improved drainage prevents adverse effects of over-watering, like root rot and soggy soil. The soil moisture remains even, and the roots cannot circle at the bottom like in traditional pots. Roots can uptake the water and nutrients they need when needed, and plants are not stressed when transplanted. 

You can build air-pruning raised beds by intentionally leaving air gaps between the lumber. The key to making this method work is ensuring there is space between the ground and the bottom of the bed to allow air circulation. To create a strong, breathable base, attach welded wire and a layer of ½-inch hardware cloth. This will support the soil while preventing it from falling through.

Fill the bed with potting mix and plant as usual. As roots grow downward and reach the air, they will self-prune—just like in an air-pruning pot—encouraging a denser, healthier root system. For best results, use adrip irrigation kit to maintain consistent moisture.

Why Air Pruning Matters

While traditional plastic pots are essential for quick-growing annuals, air-pruning is the future of gardening and farming trees, perennials, and annuals with robust root systems. One key aspect of this technology is that it allows growers extra time to prepare the plot if the weather does not permit it or if they need more time, which we all occasionally require. 

Advantages of air pruning: 

• No ability for plants to become rootbound

• Extended timeframe before transplant, creating less stress on the grower and plants 

• Tips die when they reach the air, encouraging new roots to form  

• Encourages a robust root system 

• Decreased transplant shock 

• Healthier, more vigorous plants, once transplanted, due to their extensive and healthy root systems.

• Plants uptake nutrients and water more efficiently 

• Increased yields and profitability 

Following the air pruning method, growers will experience healthier plants and improved yields for years, especially with young trees and perennial herbs. Air pruning benefits market gardeners, farmers, orchardists, serious backyard growers, nurseries, and vineyards. 

Preventing Common Growing Issues

It’s April, and the forecast still calls for freezing overnight lows and possible snow; we’ve all been there. You’re concerned your cold-sensitive bare-root trees and broccoli seedlings won’t survive the delayed planting required. Then, you remember you invested in high-quality air pruning containers and cell trays, and your stress immediately decreases. 

Air pruning pots and trays can buy you several extra weeks if you’re a northern grower waiting for a break in the weather or a busy farmer running behind on your transplanting. We’re all growers at Bootstrap Farmer, so we’ve been in your shoes. 

If you had potted plants running behind in traditional pots, their roots would almost certainly be fully encircled at the bottom. When a plant like this goes into the ground, the roots will continue to grow in this fashion, never leaving the transplant hole, becoming unable to seek water and nutrients. If you’ve had poor performance or encountered plant death but were unsure why; it could have been transplant shock and girdling caused by the effects of rootboundness. 

Alternatively, plants raised in air-pruning pots have a vast network of roots, laterally channeled to holes or permeable fabric along the sides of the pot to access air. As they burn off, more roots are formed, constantly supplying strong, healthy, vibrant roots. The result is a dense, fibrous root ball ideal for planting and a well-hydrated and nourished plant.

Suitable Plants for Air Pruning

Bare-root shrubs, trees, herbs, and annuals with robust root systems, like tomatoes and eggplant, will benefit from air-pruning. The extensive network of lateral feeder roots creates a firm, resilient rootball, supporting more extensive plant growth as they mature. These plants efficiently uptake the water and nutrients they need from every surface of their roots, quickly becoming stronger and more vibrant. 

Pro tip: Grafted trees and tomatoes will benefit significantly from this technology because their root systems are known to grow quickly and robustly. 

How to Use Air Pruning Containers

Starting crops from seed allows you to select the strongest transplants for your garden. Using high-quality seed-starting supplies and air-pruning trays will result in the most resilient transplants, ready to hit the ground running, literally. 

A few crops that benefit from transplant versus direct seed:

• Tomatoes

• Peppers

• Broccoli 

• Eggplant 

• Celery 

• Lettuce 

• Kale 

• Swiss chard 

• Squash 

You’ll notice that many items on this list are cold-sensitive summer crops that won’t tolerate cold soil or overnight lows. Start seeds like tomatoes, Swiss chard, and peppers in our 72-cell trays and up-pot them into 2.5”, 3.3” starter pots, or 5" pots. Larger seeds, like squash, can go directly into a larger pot. Pair them with 1020 trays with colors to match or mesh 1020s for good drainage. Plants won’t overstay their welcome in air-pruning pots if they must stay a few extra days or weeks, but to buy more time, offer the plants a boost of liquid fertilizer to tide them over. When selecting a tray or container size, consider their growth rate, days to maturity, and approximate transplant timing. You want them to germinate and grow properly but have enough room to grow while you’re preparing for their transplant day. Read How to Transplant and Up Pot Seedlings to learn more about up-potting. 

Filling Air Pruning Trays for Planting

To use the containers, fill them with potting soil and tamp them down with a few light drops on your working surface or tamp with another air pruning tray. Top off the soil so there is just a little room at the top. Sow your seeds appropriately based on their size and cover them with more potting soil. Tamp down the soil once more and water the seeds in. 

To use larger air pruning containers for bare-root shrubs and trees, fill the pot with potting soil, completely burying the bare roots. When it comes time to transplant the tree into the ground, remove the container to reveal a perfectly healthy rootball free of girdling or bound-up roots. Start with a 7- or 10-gallon container, and up-pot to 25 or 50 gallons in years two or three if needed. 

Common Mistakes to Avoid

• Gardeners often start seeds indoors too early, leading to rootbound and stressed seedlings. Air-pruning containers and trays help you avoid this hassle. When to Start Seeds Indoors on your Homestead explores how to find the best times for starting seeds indoors across zones and how to keep them healthy until transplant. 

• Cheap alternatives made from PVC may be tempting as opposed to high-quality air-pruning containers. Look for BPA-free, food-safe, high-density polyethylene (HDPE) plastic options. While the up-front investment is steeper than other options, these products will last longer, saving you money in the long run. 

• Growers new to air-pruning cell trays often under-water. The trays’ constant exposure to the air dries out the soil sooner than traditional containers. We recommend giving trays a deep soaking, allowing time for the water to soak in, and then going back over the trays again. Set a timer to remind yourself to check in with them every few hours as you get used to the new technique. 

• Consider bottom-watering to​​ avoid damaging vulnerable seedlings. Add ½ inch of water to the bottom tray; add more only if the surface is dry. Read Bottom-watering Seedlings and Microgreens to learn more. 

Cost and Investment: Is Air Pruning Worth It?

The cost of air-pruning trays and pots may scare some growers away, but the long-term benefits are worth it. High-quality products made with sturdy, long-lasting materials will surely last many years with proper cleaning and care. 

The return on investment will be apparent when your plants experience less transplant shock and are healthier and more productive. These improvements will lead to an extended season and increased profits. Reducing single-use plastics will also reduce the amount in landfills. Products that last for multiple seasons without damage are worth more than just the money; they’re incredibly eco-friendly. 

FAQs About Air Pruning

What plants benefit most from air pruning?

Bare root trees, annual vegetables with massive root systems like tomatoes and peppers, and perennial herbs and plants like hostas greatly benefit from air pruning. Allowing them to spend extra time in these pots before transplanting will enable them to grow without stress or become root-bound while you prepare their permanent home. 

How do air pruning pots compare to fabric grow bags?

While fabric bags are less advanced and effective than professional-grade air pruning trays and pots, they will produce better results than traditional plastic pots. Roots cannot become rootbound, leading to decreased root shock, better drainage, and healthier root systems, which leads to more productive, resilient plants. 

Do grow bags air prune?

Yes, when roots reach the porous sides of a fabric grow bag, they burn off and stop growing, leading to new, fresh roots growing. This is the same effect air pruning trays and pots have on plant roots. 

Is there a specific soil mix needed for air pruning?

Use light, well-draining potting soil so the plants can fully utilize the air-pruning abilities. Mix compost, worm castings, coco coir, or vermiculite with the soil to help with drainage and water retention.