Grow bags are a convenient solution for gardeners who are short on space, but every gardener can enjoy the benefits of grow bags. In this week’s episode, I answer all your questions on gardening in grow bags, including all the advantages as well as the challenges and how to overcome them. We polled our social media followers recently on what they wanted to know about grow bags and boy did we get a lot of questions. Answers to all of them are in this podcast and show notes.
Even though I have a big garden with 16 really large raised beds, I have added grow bags to my setup. They are useful and convenient for a number of reasons that I will expand on in this post. I always like to experiment in the garden beyond what’s growing in my raised beds. Grow bags are like pop-up mini raised gardens that allow me to temporarily add growing space. When I don’t need that space anymore, I can empty the bags and put them in storage.
Though grow bags are useful for every gardener, it’s really the urban gardeners and small-space gardeners that have the most to gain. Grow bags are perfect for gardening on a deck, patio or stoop.
Joining me on the podcast is Amy Prentice, the Director of Marketing and Communications here at Agrivana Media®. Amy used grow bags herself for the first time this growing season and shares frequently asked questions about grow bag best practices.
Before proceeding, I want to let you know that my 2021 Holiday Gift Guide is out now. You can find 20 great gift ideas for the gardeners in your life at joegardener.com/giftguide.
Grow bags have become increasingly popular for urban and small-space gardening These fabric pots provide a lightweight, portable, and affordable way to grow vegetables, herbs, flowers, and other plants in a small footprint
However, successful grow bag gardening starts from the ground up. Choosing the right potting mix is critical for healthy, thriving plants. You can’t just use any old soil in grow bags and expect great results.
In this comprehensive guide, we’ll cover everything you need to know to choose the ideal soil for your grow bags. We’ll look at:
- Why soil matters so much in grow bags
- What to avoid using as grow bag soil
- The best ingredients for grow bag soil mixes
- How to create your own custom blend
- Tips for filling grow bags with soil
Follow this advice for productive robust plants growing happily in their fabric pot homes!
Why Soil Matters in Grow Bags
Choosing the right potting mix for filling grow bags is very important. Here are some key reasons why soil makes such a big impact:
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Grow bags dry out faster than in-ground gardens. The soil needs to strike a balance between moisture retention and good drainage.
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With the limited root space in a bag, the soil should be loose and airy to prevent compaction. Restricted roots will stunt plants.
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Frequent fertilization is required since a grow bag is a contained unit. The soil needs some organic matter to release nutrients over time.
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Bags need to be lightweight for moving. A heavy soil mix will make the bags too difficult to lift and shift around.
Keep these factors in mind as you consider what to use for your grow bag soil. Now let’s look closer at specific ingredients to use and avoid.
Avoid Using Regular Garden Soil
While it might be tempting to use readily available soil from your garden, this is a mistake for grow bags. Here’s why regular garden soil won’t work well:
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Garden soil is heavy and dense, It contains lots of clay and silt particles that pack tightly together,
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All that compaction leaves little room for the air pockets that plant roots need. Drainage suffers too.
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Plant roots become stunted and twisted as they hit the impenetrable walls of hard garden soil in a confined grow bag.
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Nutrient and moisture retention are poor compared to custom mixes designed for containers.
Your plants will likely fail to thrive and may even die from the stresses of garden soil in a grow bag. Don’t give in to the temptation – avoid using any heavy clay or native soil.
Say No to Regular Potting Mix
You might think you can use any type of potting mix, but general-purpose and multi-purpose blends won’t work well either. Here’s why it’s best to skip regular potting soil:
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These mixes contain peat or coco coir as moisture-retaining ingredients. Too much moisture retention promotes root rot in the snug grow bag space.
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Potting mixes are formulated for traditional rigid containers that restrict water uptake. Grow bags need faster drainage.
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Standard potting mixes will be too heavy once moist, making the bags difficult to move. They don’t dry out fast enough.
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Nutrient levels tend to be low in basic all-purpose potting soils intended for short-term plants.
For prolific harvests from healthy plants, a specially tailored soil blend is needed for the unique grow bag environment.
The Best Soil Ingredients for Grow Bags
The ideal potting mix for grow bags includes these components:
Compost
Compost improves drainage while also adding nutrients. The crumbly texture creates air pockets for roots while increasing the soil’s ability to retain moisture. Compost brings the benefits without the drawbacks of peat and coir. Use compost from fully finished, high-quality sources.
Coconut Coir
Coir is a sustainable peat moss alternative. The long coconut fibers create lots of air space. Coir absorbs and holds onto water but still allows excess moisture to drain away. It’s lightweight and resists compaction. Use coir in moderation to avoid overly wet soil.
Vermiculite
Vermiculite is a mineral that expands when heated into accordion-like pieces filled with air pockets. It retains 4-5 times its weight in water and keeps soil loose while improving drainage. Vermiculite is very lightweight.
Perlite
Perlite consists of volcanic glass popped into white, porous nuggets. It aerates soil and holds moisture while still permitting quick drainage. Perlite prevents compaction issues in grow bags. Don’t use too much, as it holds less water than vermiculite.
Sand
A small amount of coarse builder’s sand or horticultural sand provides drainage assistance. The large particles maintain air spaces between them. Too much fine sand can compact, so use sparingly.
Mixing Your Own Custom Soil Blend
While pre-mixed soils for grow bags are available, you get more control and save money by making your own. Just follow this simple recipe:
- 1 part compost
- 1 part coir or peat moss
- 1 part vermiculite or perlite
Thoroughly mix the ingredients together into a uniform blend. Test the drainage and moisture retention as you fine-tune the proportions to suit your conditions.
If using peat instead of coir, be sure to pre-moisten it so it can absorb water when mixed. Break up any large clumps.
For extra nutrients, also mix in a cup or two of worm castings per cubic foot of soil. The castings will add beneficial microbes.
Tips for Filling Grow Bags with Soil
After creating the ideal soil blend, follow these tips for transferring it into your grow bags:
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Moisten the mixed soil before filling bags so it packs together well. Dry soil is hard to properly compress and settle.
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Pack the soil into bags firmly every 3 inches, eliminating air pockets that can dry out roots. But leave the top 2 inches looser.
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Consider placing an inch or two of compost or manure on top of the soil to act as a moisture-retaining mulch that supplies nutrients.
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Water thoroughly after planting to further settle the soil and eliminate any remaining large air pockets.
With the right filling and preparation methods, your plants will get off to a great start in their cozy grow bag homes.
Get Growing!
Now you’re fully prepared to create the ideal soil mix to fill your fabric grow bags. Follow this guide, using well-draining but moisture-retentive ingredients, for thriving container plants.
Pay close attention to properly filling and settling the soil in the bags. With this knowledge and the perfect potting blend, you’ll be on your way to a productive grow bag garden!
Spacing Plants When Using Grow Bags
Most grow bags are cylindrical while — Cindy from the joegardener Facebook group points out — most spacing guidance for plants is based on a square.
To give plants adequate space within a grow bag, I eyeball the square within the circle. That leaves four semi-circles on the periphery where more plants could potentially fit.
What Soil Should Be Used in Grow Bags
Grow bags require well-draining soil that retains just enough moisture so the root mass will not dry out between waterings. Bagged products labeled as potting soil or container mix are ideal.
Many potting soils contain peat moss but more and more mixes are now using coir (coconut fiber) instead. And then there is perlite, those white beads that look like pieces of styrofoam. Perlite is a mineral that retains moisture and makes potting mix lighter. Alternatively, the mix may contain vermiculite, which is flaky and serves the same purpose as perlite.
Bagged mixes may also contain wood fines or forest products, which is just finely ground wood.
You don’t have to use new soil each year unless soil-borne diseases have made their way into your grow bag. Research the diseases that occurred on the plants. You’ll discover if the pathogens are soil-borne. Or you can have the soil tested for pathogens at your local extension service.
To use clean soil again another year, you can refresh it by dumping the soil out into a wheelbarrow or large container that it can expand in. Pick out any clumps or woody roots then add compost. The additional compost should amount to about 25 percent of the original volume of the soil. The compost will provide the nutrients and microbiology that plants need to succeed. You can also add slow-release organic fertilizer.
I’m often asked about planting in straight compost. While you can get great results in compost, it doesn’t have everything that plants need. Even though compost is quite diverse on its own, plants require diverse minerals and nutrients that aren’t found in great numbers in straight compost. Your compost can be amended with lime, wood fines and perlite/vermiculite to produce a better container mix.
How to Choose BAGGED SOIL for Your Garden
FAQ
What is the best soil mix for grow bags?
When it comes to selecting the right soil mixture for grow bag gardening, I like to use a base of potting mix and compost at about a 2:1 or 3:1 ratio. I like this mixture because grow bags are still containers and they must be able to drain.
What should I put in the bottom of my grow bags?
Place a thin layer of rocks or sticks at the bottom of your grow bag to ensure good drainage. Fill your grow bag nearly to the top with your soil, leaving about four inches at the top. Layer two inches of compost on top of the soil. Plant!
What kind of soil do potato grow bags need?
Place about 6in of good quality potting soil in the bottom of the bag. You can mix in 3-4 quarts of compost or aged manure ahead of planting, or top dress afterwards. Too much nitrogen will cause lush top growth at the expense of tubers. Do not use fresh manure as it can cause potato scab.
What is the best material for a grow bag?
The best material for grow bags is heavy-duty landscape fabric, which is typically made from polypropylene. The material is typically food-grade, free of anything harmful and long-lasting. Another common landscape fabric material is polyethylene, which is basically recycled plastic bottles.
What is the best soil for grow bags?
The best type of soil for grow bags is a high-quality potting mix or a blend designed specifically for container gardening. These mixes are typically light, well-draining, and contain organic materials such as peat moss, coconut coir, or composted bark.
Can you grow plants in bags?
One of the most important factors in having success growing plants in bags is choosing the right soil. Using regular garden soil or potting mixes will lead to failure. This comprehensive guide will walk you through everything you need to know to choose the ideal soil for thriving plants in grow bags.
Can you use garden soil in grow bags?
It may contain a mix of sand, silt, clay, organic matter, and various microorganisms. While it can be a valuable resource in gardening, there are specific considerations to be aware of when using garden soil in grow bags. Using garden soil in grow bags comes with its own set of advantages and disadvantages that every gardener should consider.
What plants grow well in grow bags?
Certain plants thrive exceptionally well in grow bags compared to traditional garden soil. Vegetables like tomatoes, peppers, and cucumbers particularly benefit from the drainage and aeration provided by grow bags. These plants have root systems that require ample space and oxygen, which grow bags facilitate effectively.
Do you need to fertilize a grow bag?
For grow bag gardening to work, you need to fertilize because the soil inside the bag is all the food your plant needs. Because grow bags drain so well, nutrients from your potting soil will flush out with regular watering. Consider adding a slow release fertilizer to your soil before you even plant.
What is a grow bag?
Grow bags are an increasingly popular way to garden, especially for urban gardeners or anyone with limited space. Grow bags provide an easy and portable way to grow vegetables herbs fruits and flowers. One of the most important factors in having success growing plants in bags is choosing the right soil.