Fabric grow bags are quickly becoming the preferred plant container for gardeners big and small. The switch to fabric bags began with Dutch arborists in the late 19th Century, but it wasn’t until the 1970’s that the idea took off in North America. Since then, growers have flocked to the concept for its unique advantages over non-porous (plastic and glazed earthenware) containers. If you are looking to increase yields, fight root-rot, and grow economically, you need to understand how to use fabric grow bags to their best advantage
Fabric Grow Pots
Fabric grow pots are flexible, lightweight containers made of woven material. They can be made from a range of fabrics, from felt to woven grasses to recycled plastic (polypropylene); high-quality containers may include proprietary synthetic textiles. Fabric bags come in a tremendous range of sizes, far surpassing the largest plastic containers on the market.
These flexible growing containers have become popular for a number of reasons. They are durable, easy to store, and inexpensive. Making the switch from plastic to fabric has many benefits — but they also require you to adjust some of your gardening routines. Knowing how to use fabric grow bags properly will bring out the best in your plants.
Root Pruning Pots
Root pruning pots are designed to allow air to permeate the outer soil layer. When the tip of a growing root contacts dry air, it stops growing outward. Instead, the plant invests in growing many fibrous offshoots from the sides of the newly pruned root tip.
These pots are useful when your crop depends on a robust root system. This includes plants that you plan on transplanting and plants that will later bear fruit. When it comes to root pruning pots, it is hard to beat the natural breathability of fabric.
Although less common than fabric pots, root pruning pots can also be made from hard plastic. This style features a pattern of large holes to expose the soil to the air. When designed with care, some of the visual effects can be quite striking. Another advantage of solid plastic pruning pots is longevity — they are immune to punctures and tears that may end the life of a fabric bag. Finally, their rigidity makes them a better fit for large-scale operations that need precision sizes for storage and marketing.
Fabric root pruning pots do have a few advantages over the solid version. Fabric bags can be manufactured in larger sizes. There is no danger of your soil (or other grow medium) falling out of the containers through the holes. The exchange of air between container and environment is also more even than in a solid pruning container. The structure of a solid pot creates areas of soil that are either fully exposed to the air, or not at all. The fabric ensures even air exchange and balanced growth throughout the soil.
Plant Pot Sizes Chart
Traditionally, plant containers have been measured by volume (gallons or liters) and/or diameter (inches or centimeters). (U.S. or metric ). Small containers may be measured by diameter alone, and larger plastic containers often list both diameter and volume. Plant containers are also given size ranges (i.e., size #1, size #2 . . .) that tell the gardener relative size, but not actual.
However, what should be a simple method of sizing pots is quickly muddied when you learn that plant nurseries have adopted their own definitions of ‘gallon’! In the last 75 years, different nurseries have independently decided that they would use the word ‘gallon’ to describe a container volume of anywhere between .7 and 1.1 standard gallons. This gardener’s conundrum is quickly addressed by a writer at Sprigs and Twigs with a chart that helps sort out the differences between U.S., metric, and nursery sizing. If you want an exhaustive explanation, the American Horticultural Society is happy to oblige you.
The fabric grow bag industry seems destined to follow in the convoluted measuring footsteps of its rigid container predecessors. For the average gardener, this imprecision is irrelevant. For a grow bag user, the imprecision actually makes an odd bit of sense — after all, the bag’s volume is in fact flexible.
Beyond physical measurements, keen gardeners will also keep in mind qualitative traits when sizing up their pots. Color and material choices are more than aesthetic; dark colors absorb heat, and fabrics provide different levels of insulation.
Sizing Your Containers
With such a wide range of container sizes, how do you know what size to use? Making the right choice is essential. “Improper container sizing for the plant is the number 1 reason plants die in container food production.” There are probably as many ideal sizes as there are crops to grow, but beginning with a few size categories should get you well on your way to success.
The first size category of grow bags is 5 gallons and under. Leafy greens like lettuce, as well as annual flowers, have a shallow root system and do well in fabric bags in this size range. Peas, peppers, and a number of other popular vegetables do well in this range of pot sizes.
5-15gallon (~19-57 L) pots are good for fruit-bearing plants that need deeper roots and more soil to draw nutrients from. Tomatoes, grapes, and berry bushes do well in containers this size.
Bag sizes continue to climb – up to 400 gallons! Topiary enthusiasts should be working with bags in the 20- 50 gallon (~190 L) size. Arborists should be looking at the 100+ gallon sizes to ensure that their saplings have room to form a root ball that can survive transplanting.
If you are uncertain what you will be growing, or if you are looking to add a number of general-purpose containers to your garden, 5-gallon pots are a good choice. They are roomy enough for most plants and small shrubs a home gardener wants to grow; and at 60 or so pounds (~28 Kg) when filled, most gardeners can manage moving one without undue strain.
When deciding which fabric bags to go with, be sure to pick ones with the sizes your plants need. North Carolina State has provided gardeners with a list of common crops and their container volume needs. It may take you a few seasons to find the ideal size for each kind of plant — but isn’t discovering what works for you part of the joy of gardening?
Pros and Cons of Grow Bags
There is no single, ideal growing container. While it is likely that every gardener can make good use of a fabric grow bag, there are still situations where a traditional container is a better choice. Let’s take a look at the pros and cons of fabric grow bags.
The Pros of Fabric Bags
The most often cited benefit of using fabric grow bags is that they encourage a healthy root system. Fabric bags allow air exchange around the surface area of the entire pot, not just the surface. Air exchange brings gasses such as oxygen, nitrogen, and carbon dioxide into the soil. The air feeds the plants and microbial life. It also prunes the tips of the outermost roots, which encourages broader root growth.
Fabric bags are durable. Will they last forever, like plastic? No — but for 21st Century growers, using degradable containers may be the biggest pro of all. The actual lifespan of fabric grow bags varies greatly. Sun exposure, type of crop, relocation, and product quality all play roles in your container’s lifespan. All told, the consensus seems to be that you can expect 3-8 years of life from your bag.
Handles are an undervalued asset when it comes to containers. Great leverage, easy on the hands. Look for bags with double-stitched handles wide enough to handle a good yank. Some of your larger plants may be easier to drag than lift; remember, ten gallons of soil weighs over a hundred pounds (~50 Kg). If you grow big, it’s worth paying for bags with reinforced handles (and durable bottom). And for you ornamental growers, handles also make it easy to turn the pot to display the plant’s best features.
Fabric grow bags are surprisingly economical. If you are uncertain about fabric bags, or unable to invest in your dream array of containers, you can buy containers made of recycled polypropylene. A 5-gallon container of this type can cost as little as two dollars. The caveat with economical bags is that you need to be prepared to replace everything after a few seasons. Investing upfront in quality bags is a must for the seasoned gardener.
You can find another pro for fabric bags on the microscopic level. The improved aeration provides oxygen for the microorganisms that inhabit healthy soil. Whereas solid containers can imitate anaerobic conditions, fabric bags allow oxygen to permeate your soil.
A final pro for fabric grow bags is their flexibility. Plastic pots are virtually identical to one another in terms of permeability, weight (density). Increasing the thickness of plastic can give you some control over heat insulation, but beyond that solid containers are all the same. Contrast that with the variables available to makers of fabric containers: absorption and insulation of various materials, weaving methods, customizable sizes . . . the list goes on. You can also take fabric bags’ literal flexibility as a pro. Cram one into the corner of your patio or delicately wedge one between fence posts. Try doing that with terra cotta!
The Cons of Fabric Bags
There are situations where fabric containers are not ideal. They may look frumpy or spill soil. Their permeable nature means they dry out quickly, especially for smaller containers. That means more water consumption and more of your attention required.
Fabric’s root pruning benefit comes with a con of its own. A fabric bag can be too successful at drying out root tips. Air absorption on all sides can shrink’ a pot’s usable diameter by up to an inch. That means that your plant’s roots can’t access the outermost layer of soil in your bag. Is this loss outweighed by the more efficient root growth through the rest of the soil? Sounds like an experiment worth a few tomato plants to find out.
Best Fabric Pots
Dozens of merchants have sprung up to match the growing popularity of fabric grow bags. And, as with any product, quality varies… But beyond quality, consider a few more variables to get the most from your grow bags.
Although fabric is relatively inexpensive, durability and craftsmanship are worth paying more for. Especially if you move your plants often or expose them to extreme weather, it is worth seeking out high-quality vendors.
The fabric used in pots can be cloth or plastic. Cloth bags are more malleable and breathe better. Plastic retains both heat and moisture. Along with the material, consider the tightness of the textile weave. Tighter threads means better water retention, but less effective air exchange. Find a manufacturer that can match your needs.
Consider Your Climate
If you grow in a hot climate, you need to choose fabric bags that mitigate the effects of heat. Choose a multi-ply bag in a light color to combat evaporation. Find ones with sturdy handles so you can move your plants into shady areas.
Similarly, if your climate is damp, plan to use bags that minimize its dangers. Choose a loose-weave fabric to encourage evaporation and help avoid root rot. Use those handles to move your plants into a sun-powered drying zone.
Know your growing zone and plant accordingly. The right fabric grow bag can help you stretch your limits, but — well you know Mother Nature will eventually push back.
There are plenty of good reasons to switch from solid growing containers to fabric grow bags, and gardeners everywhere are catching on. With quality vendors and a Healthy roots and higher yield, economic and ecological advantages, and more flexibility in what and where you grow — all these benefits await you when you switch to fabric grow bags, so don’t get left behind.