Grow bag gardening might be a new concept for you as a beginner gardener. If you have never grown plants in grow bags before, it’s a lot like container gardening, except the containers are grow bags. Some gardeners, like me, love using grow bags as a supplement to their existing garden.
While I do enjoy grow bag gardening, it’s not without is challenges. What should you and shouldn’t you do when you’re grow bag gardening? This way, if you decide to give it a try, you can have the most success.
Before we start, you can watch a podcast episode about the dos and don’ts of grow bag gardening here: Grow Bag Gardening: DO’s
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. 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.
Why Soil Matters in Grow Bags
Choosing the correct soil mixture is critical because grow bags have different needs than in-ground gardening. Here’s why the soil matters so much
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Grow bags dry out faster than in-ground beds. The soil needs to hold moisture but still drain well.
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With limited root space, the soil should be loose and airy. Compaction will restrict roots.
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Frequent fertilization is needed. A soil with some organic matter will supply nutrients over time.
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The bags need to be lightweight when moving them. A heavy soil mix will be too difficult to lift.
Now let’s look at what to use to create the perfect soil blend.
Avoid Regular Garden Soil
It’s tempting to use soil dug up from your garden, but this will result in thick, compacted soil. Garden soil is too heavy.
It contains lots of clay and silt particles that cling together tightly. This prevents proper drainage and air pockets that roots need.
Roots will become stunted and plants will fail to thrive in dense garden soil inside a grow bag. Don’t make this mistake!
Say No to Regular Potting Mix
General purpose and multi-purpose potting mixes are too heavy for use in grow bags.
They contain peat or coir which retains moisture well. But in a bag’s limited space, they will hold too much water leading to root rot.
These mixes are designed for a rigid container that restrict water uptake. Grow bags need a lighter, faster draining soil.
The Best Soil Ingredients for Grow Bags
To create an ideal soil blend, use a combination of these soil amendments:
Compost
Compost adds nutrients and improves drainage. It has a loose, crumbly texture that creates air pockets. Compost increases moisture retention but still allows excess water to drain.
Coconut Coir
Coir is a sustainable alternative to peat moss. It has excellent water holding capacity but is still lightweight. The threadlike structure creates lots of air space.
Vermiculite
Vermiculite is a mineral that forms thin, spongy pieces. It’s very lightweight and absorbs 4-5 times its volume in water. The air spaces vermiculite creates prevent compaction.
Perlite
Perlite consists of volcanic glass formed into lightweight, porous pieces. It helps aerate the soil and hold moisture while still draining well. Perlite keeps soil loose.
Sand
Sand particles are large enough to maintain air spaces between them. Sand improves drainage to prevent overly wet soil. A small amount of coarse sand is optimal.
Mixing Your Own Custom Soil Blend
You can buy pre-mixed soil for grow bags, but it’s easy and economical to make your own.
Follow this simple recipe:
- 1 part compost
- 1 part coir or peat moss
- 1 part vermiculite or perlite
Mix the ingredients together thoroughly. Your custom mix will be loose, lightweight and fast-draining. But it will still hold the moisture your plants need.
If using peat instead of coir, moisten it before mixing to avoid it repelling water later. Break up any large clumps.
For a nutrient boost, also mix in a small amount of worm castings. It will add beneficial microbes and provide slow-release nutrients.
Tips for Filling Grow Bags with Soil
Once you’ve created the ideal soil, follow these tips when filling grow bags:
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Moisten the soil before adding it to bags so it’s easier to thoroughly pack it in. Dry soil can be hard to compress.
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Completely fill bags, eliminating air pockets. Gently tamp down every 3 inches. This prevents soil settling over time.
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Leave 2 inches of space at the top for watering. Don’t compact this top layer.
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For taller plants, put a few inches of compost or manure on top for nutrients.
Now that you know what makes the best soil for grow bags, you’ll be ready for thriving plants! Follow this guide to create the ideal lightweight, fast-draining and nutrient-rich mix.
Be Prepared To Irrigate
Irrigation is key with grow bag gardening, but you must be prepared. If you plan to hand water, then I’d suggest you try the water, wait, water method. You would water it a little, wait for it to sink, and then water it some more. That way your water won’t immediately seep out of the sides.
You could also put your grow bags in a tub and let the water drain out. The water will be absorbed from the bottom up as it drains.
You can also use drip lines. Epic Gardening has very nice lined grow bags that allow you to add a tidy drip line up the back. Hook the drip lines to your gardening watering system and you won’t have to worry about hand watering. (You can view Epic Gardening’s grow bags at my affiliate link here.)
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. As your growing season continues, add a liquid fertilizer every couple weeks.
Don’t Plant in Too Small of a Grow Bag
When using grow bags, the size of your bag is a big concern. You don’t want your plant roots to outgrow your bag, because if they do, they will stop producing.
One year I planted 1 tomato plant in a 7 gallon grow bag. It did great at first and produced a large crop. But as the growing season went on, it stopped making any fruit at all, and I saw that its roots had spread all over the bag. Its roots would have been able to spread out even more if I had planted it in a bigger bag. This year, I’m going to try a 15 gallon grow bag instead.
In hot places, using a bigger grow bag is especially important because your plants will have more time to grow.
How to Make An All Purpose Garden Soil from 3 Bagged Products: Cheaper & Better Than Any Bagged Mix!
FAQ
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