How Much Soil for 5 Gallon Grow Bag
Table of Contents
- Introduction
- The Short Answer for Soil Volume
- Soil Volume Conversion Chart
- Why Soil Volume Changes After Filling
- Choosing the Best Soil Mix for 5 Gallon Bags
- How to Fill Your 5 Gallon Grow Bag Correctly
- What Can You Grow in 0.67 Cubic Feet of Soil?
- Managing Water and Nutrients in 5 Gallon Bags
- Summary Checklist for Buying Soil
- Conclusion
- FAQ
Introduction
Finding the right amount of soil for your garden shouldn't feel like a high school math test. Many home gardeners switch to fabric containers because they offer excellent drainage and aeration, but standing in the garden center aisle trying to figure out how many bags of potting mix to buy can be frustrating. Whether you are starting a pepper patch on your balcony or setting up a row of tomatoes in your backyard, getting your soil volume right is the first step toward a healthy harvest. At Garden Greenland, we want to make sure you have the exact measurements you need to get growing without multiple trips to the store. This post will cover exactly how much soil you need for a 5 gallon grow bag and how to account for settling and plant space.
The Short Answer for Soil Volume
If you are looking for a quick calculation to take to the store, here is the standard measurement for a single 5 gallon container.
Quick Answer: A standard 5 gallon grow bag holds approximately 0.67 cubic feet of soil. Since most standard bags of potting mix are sold in 1 or 2 cubic foot sizes, one 1-cubic foot bag will fill about one and a half 5 gallon grow bags.
While "5 gallons" sounds like a liquid measurement, soil is sold by volume in cubic feet or quarts. Because fabric grow bags are flexible, their actual capacity can vary slightly depending on how wide or tall the specific brand is manufactured. However, the 0.67 cubic feet rule is the most reliable estimate for planning your garden. If you need new containers, browse our grow bags collection to compare sizes and styles.
Soil Volume Conversion Chart
To help you plan for multiple containers, use this table to determine how many bags of soil you should bring home. Most premium potting mixes are sold in 1.5 cubic foot bags, but we have included 1 and 2 cubic foot options for easy reference.
| Number of 5 Gallon Bags | Total Cubic Feet Needed | 1 cu. ft. Bags | 1.5 cu. ft. Bags | 2 cu. ft. Bags |
|---|---|---|---|---|
| 1 Bag | 0.67 cu. ft. | 1 bag | 1 bag | 1 bag |
| 3 Bags | 2.01 cu. ft. | 2 bags | 2 bags | 1 bag |
| 5 Bags | 3.35 cu. ft. | 4 bags | 3 bags | 2 bags |
| 10 Bags | 6.70 cu. ft. | 7 bags | 5 bags | 4 bags |
Why Soil Volume Changes After Filling
It is a common mistake to buy exactly 0.67 cubic feet of soil and find that the bag is only three-quarters full. There are three main reasons why you should always "round up" when purchasing your growing medium.
Soil Settling and Compaction
When you first pour dry potting mix into a fabric bag, it is full of air. As soon as you water it for the first time, the particles settle together, and the air pockets collapse. This often causes the soil level to drop by two or three inches. Most gardeners find they need about 10-20% more soil than the raw volume suggests to account for this initial settling.
Room for Watering
You should never fill a grow bag all the way to the very top rim. If the soil is flush with the edge, water will simply run off the sides instead of soaking down to the roots. We recommend leaving about 1 to 2 inches of "headspace" at the top. This acts as a reservoir that holds water while it slowly filters through the soil.
Root Ball Displacement
If you are transplanting a large nursery start, such as a gallon-sized tomato plant, the root ball itself will take up space. In this case, you will actually need slightly less loose soil because the plant's existing dirt and roots act as "filler."
Key Takeaway: Always buy one extra bag of soil more than your calculations suggest. It is better to have a little left over for top-dressing than to run out when you have one half-filled bag left.
Choosing the Best Soil Mix for 5 Gallon Bags
A 5 gallon grow bag is a closed environment. Unlike plants in the ground, container plants cannot send roots deeper to find water or nutrients. Therefore, the quality of the soil you put in that bag is the single most important factor in your success.
Avoid using "Garden Soil" or "Topsoil." These products are too heavy for containers. They lack the aeration needed for fabric bags and will often compact into a hard, muddy brick that suffocates roots. Instead, look for a high-quality "Potting Mix" or "Container Mix."
A great DIY mix for a 5 gallon bag usually includes:
- Peat Moss or Coconut Coir: To hold moisture.
- Perlite or Vermiculite: To ensure drainage and prevent compaction.
- Compost or Aged Manure: To provide slow-release nutrients.
At Garden Greenland, we often see beginners struggle with watering because their soil is too heavy. If your bag feels extremely heavy and stays soggy for days, you may need to add more perlite to your next batch to improve the air-to-water ratio. For pre-made mixes labeled for container use, check our Garden Pots & Planters collection to find potting mixes and containers that work well together.
How to Fill Your 5 Gallon Grow Bag Correctly
Filling a grow bag is slightly different than filling a plastic pot because the walls are flexible. If you don't fill it correctly, the bag can end up slumped or lopsided.
Step 1: Prep the bag. Unfold the grow bag and pull the sides up. If the fabric is stiff, you can fold the top couple of inches down like a cuff to give the bag more structure while you fill it.
Step 2: Add the base layer. Pour in the first 3 to 4 inches of soil. Press down lightly with your hands to ensure the bottom corners are filled out. This creates a sturdy "foot" for the bag to sit on so it doesn't tip over.
Step 3: Fill and hydrate. Continue adding soil in batches. After every 6 inches of soil, give the bag a quick shake and a light spray of water. This helps the soil settle naturally as you go, rather than waiting for one big collapse after the plant is already in.
Step 4: Set the plant level. Place your plant in the bag and fill around the sides. Ensure the final soil level—after the plant is in—is about 2 inches below the rim.
Bottom line: Proper filling ensures your grow bag stays upright and provides a stable environment for root development throughout the season.
If you want step-by-step growing tips specific to fabric containers, read our guide on how to grow veg in grow bags.
What Can You Grow in 0.67 Cubic Feet of Soil?
The 5 gallon grow bag is the "Swiss Army Knife" of container gardening. It is large enough to support significant root systems but small enough to move around your patio.
- Tomatoes: One determinate (bush) variety per bag. Indeterminate varieties can grow in 5 gallons, but they will require much more frequent watering and heavy feeding.
- Peppers: One large bell pepper or two smaller chili pepper plants.
- Eggplant: One standard eggplant or two "fairy tale" miniature varieties.
- Root Vegetables: You can fit about 10–12 carrots or 15–20 radishes in the surface area of a 5 gallon bag.
- Leafy Greens: 3 to 4 heads of lettuce or a thick planting of spinach.
- Potatoes: You can plant 2 seed potato pieces in a 5 gallon bag.
If you are planning to grow larger crops like squash or melons, you might want to look into our larger Garden Pots & Planters or bigger options within the grow bags collection. For more on choosing the right size, see our post on what size grow bags do I need for my garden.
Managing Water and Nutrients in 5 Gallon Bags
Because a 5 gallon volume is relatively small, it can dry out quickly on hot summer days. Fabric bags are breathable, which is great for the roots but means moisture evaporates from the sides as well as the top.
If you find yourself watering more than once a day, consider a more automated approach. We recommend looking into our Watering & Irrigation collection for simple solutions. A basic drip system or an automatic timer can keep your 0.67 cubic feet of soil consistently moist, which prevents issues like blossom end rot in tomatoes. Browse specific options like our Automatic Micro Home Drip Irrigation Watering Kits or the 25M Micro Drip Irrigation System for easy installs.
Additionally, because you are watering frequently, nutrients will leach out of the bottom of the bag over time. Plan to use a liquid fertilizer or a top-dressing of compost every 2 to 3 weeks during the height of the growing season to keep your plants productive. For more on watering frequency and tips, read our guide on how often to water tomatoes in grow bags.
Summary Checklist for Buying Soil
Before you head to the garden center, keep this quick checklist in mind to ensure you have everything you need for your 5 gallon grow bags.
- Calculate the total: Multiply your number of bags by 0.67.
- Factor in the extras: Add 15% to that total for settling and compaction.
- Check the bag size: Look at the "Volume" section on the soil bag label (usually listed in cubic feet).
- Pick the right mix: Ensure it is labeled for "Containers" or "Pots."
- Don't forget the food: Pick up a balanced fertilizer, as potting mix nutrients are usually used up within 6 weeks.
Key Takeaway: Success with 5 gallon grow bags comes down to high-quality potting mix and consistent moisture levels.
If you need tools to make planting easier, consider a garden tools set and a pair of durable garden gloves before you start.
Conclusion
Understanding how much soil for a 5 gallon grow bag is the foundation of a successful container garden. By planning for roughly 0.67 cubic feet per bag and accounting for a little extra for settling, you can ensure your plants have the room they need to thrive. Whether you are a beginner or a seasoned gardener, using the right tools—from the bags themselves to your garden tools set—makes the process more enjoyable. Our mission at Garden Greenland is to provide the reliable equipment you need to feel confident in your green space. Now that you have your measurements ready, it's time to grab your garden gloves and start planting.
FAQ
Is a 5 gallon bucket the same as a 5 gallon grow bag?
In terms of volume, they are very similar, both holding about 0.67 cubic feet of soil. However, a grow bag provides better air circulation to the roots, which prevents root circling and encourages healthier growth compared to a plastic bucket. For a deeper comparison, see our article on which is better: grow bags or pots?
How many quarts of soil are in a 5 gallon grow bag?
There are approximately 20 to 22 quarts of soil in a 5 gallon grow bag. If you are buying small bags of specialty soil measured in quarts, you will need about one and a half 16-quart bags to fill one container.
Can I reuse the soil in my grow bags next year?
Yes, you can reuse the soil, but it needs to be refreshed. Over the season, the plants will consume the nutrients and the soil will compact, so we recommend mixing in some fresh compost or a slow-release fertilizer before replanting. For tips on fabric bag longevity and re-use, read are grow bags toxic? Understanding the safety of fabric planters.
Do I need to put rocks at the bottom of my 5 gallon grow bag?
No, you should not put rocks in the bottom of a grow bag. Fabric bags already have excellent drainage through the material itself, and adding rocks actually raises the water table inside the bag, which can lead to root rot. For drainage best practices, see our post on do grow bags need drainage holes?
