"What soil should I use in my GreenStalk?" is one of our most frequently asked questions. For years, we've recommended Happy Frog potting mix for its reliable performance, but with prices climbing higher and higher, we wanted to find more affordable alternatives that still deliver great results.
We turned to our Facebook community to ask what soils you wanted us to test. Based on your feedback and what's commonly available across different regions, we selected four contenders and put them through a real-world growing trial. The results surprised us — and they might surprise you too.
The Testing Setup
We tested four different potting mixes under identical conditions:
Every planter received the same treatment: identical amendments (Fox Farm Organic Jump Start Fertilizer and worm castings), the same watering schedule, and the same crops planted on the same day.
From left to right: Kellogg's Organic, Black Gold Organic, Expert, Black Gold All Purpose
What We Looked For
All four soils shared similar base ingredients: peat moss, forest products, and perlite. But, they differed in their built-in fertilizer content and special additives. Here's how they ranked in terms of pre-loaded nutrients:
Black Gold All Purpose (highest)
Black Gold Organic
Kellogg's Organic
Expert (lowest)
We also paid close attention to moisture retention, weight, and how the soil structure held up over time. These factors are especially important for vertical planters, where you need soil that stays light but holds enough water to keep plants hydrated between waterings.
The Results
Black Gold All Purpose - The Clear Winner
This soil delivered the best overall performance across the board. Plants grew larger, the soil maintained excellent moisture levels while staying light and fluffy, and we saw strong results with every crop we planted. The kale and beets were particularly impressive.
What sets Black Gold All Purpose apart is its higher built-in nutrient content combined with additional amendments like worm castings. The soil struck the perfect balance between drainage and moisture retention—critical for vertical gardening where water management can be tricky.
Black Gold Organic - A Close Second
The organic version performed nearly as well as the All Purpose, with just slightly smaller plant growth overall. This soil includes rice hulls and other organic materials that help it stay light while retaining moisture well.
While it clumped together slightly, it maintained a good structure and kept plants hydrated. The spinach and Swiss chard looked great, though the kale wasn't quite as robust as in the All Purpose mix.
Expert (Walmart) - The Surprise Performer
We'll be honest—we didn't have high hopes for the cheapest soil in our test. With the lowest built-in amendments, we expected it to struggle. Instead, Expert proved that quality amendments can genuinely improve budget soil.
The moisture retention was good, plants looked healthy, and the overall performance was solid. This was the surprise of the test, showing that you don't necessarily need to spend big to get decent results—as long as you're willing to supplement with good amendments.
Kellogg's Organic - Needs Modification
This is where we saw the most challenges. The Kellogg's mix contains sand, which isn't ideal for container gardening, and the bag was extremely heavy—a red flag for vertical planters.
Throughout the test, this soil dried out significantly faster than the others. Even when there was moisture deeper in the soil (always dig down to check!), the surface was dry and crispy, and plants showed wilting that we didn't see in the other mixes. The beets did surprisingly well despite these conditions, but overall, this wasn't our favorite performer.
The Amendment Factor
Perhaps the most important finding from this test: quality amendments make a significant difference, even with cheaper soils. Every planter received the same treatment with Fox Farm Jump Start granular fertilizer and worm castings, and this consistent feeding helped level the playing field.
The Expert soil, our cheapest option with the least built-in nutrients, performed far better than expected. This proves you can stretch your gardening budget by investing in good amendments rather than only premium soil.
Note: Some less expensive potting soils contain a lot of wood pieces. It’s best to remove these, particularly the large pieces, so they don’t obstruct root growth or grow mold.
A Note About Regional Availability
Keep in mind that soil formulations can vary by region, and not all brands are available in all states, so the exact product you find at your local store might differ slightly from what we tested. That said, these results should give you a solid starting point for making informed decisions about what works best in your area.
From left to right: Black Gold Organic, Black Gold All Purpose, Expert, Kellogg's Organic
You've Got Options
You don't have to spend a fortune on premium potting mix to grow a successful GreenStalk garden. Our test proved that mid-range soils like Black Gold All Purpose offer excellent performance at a reasonable price, and even budget options can work well when you invest in quality amendments.
No matter what you choose, look for soil that's light but retains moisture, check for built-in nutrients (or plan to supplement beyond the basics), and don't judge moisture levels by surface appearance alone — dig deep to see what's really going on.
Here's to growing more while spending less. Happy gardening!
