Rock dust has gotten much hype recently as a gentle, organic remineralizing soil additive. However, there’s also a lot of misinformation regarding this gardening product, and determining whether it is beneficial, neutral, or harmful for your soil is a topic of hot debate. So, is rock dust a suitable additive for your garden, or is it just a scam?
You can use rock dust in your garden, but it probably won’t make a difference to your plant’s growth. Most soils already contain all the necessary minerals for plant growth, and rock dust is no better for your garden than adding raw rocks to your soil.
So, let’s break this topic down and look at the facts. I’ll help you understand why rock dust isn’t beneficial for your garden plants and bust some rock-dust-related myths.
Why Do People Add Rock Dust to Their Gardens?
People add rock dust to their gardens because seller claim it adds essential nutrients to soil, balances bacterial growth, and adjusts the pH of your garden. However, these claims are not completely accurate.
Rock dust, which contains tons of natural minerals, seems like a natural choice when you need to fertilize your plants and keep your garden beds in check. However, the popularity of rock dust is more of a testament to effective marketing strategies than increased crop yields and plant health.
Rock Dust Is a Profitable Product
Rock dust is a byproduct of quarrying stone, and before rock dust became a gardening craze, no one knew what to do with it. However, by packaging and selling this dust as a soil additive, quarries realized they could offload this stuff as fast as they could produce it, keeping their quarries clear and making money while they did it.
For example, Harrison Hall of Cascade Compost revealed that his company sold over 100 tons of rock dust a year in this interview. That equates to thousands and hundreds of thousands of dollars in profit – just to sell something that was once regarded as a waste product
In fact, for the most part, you’ll only see positive claims about rock dust coming from people who work in the industry. The curious researchers who have dug for the facts amidst pervasive advertisements, on the other hand, have found evidence that this product is essentially a scam.
People Claim That Rock Dust Is a Soil Booster
Marketing teams advertise that rock dust adds minerals to your soil, thus encouraging the growth of healthy bacteria and helping you raise the pH of your garden.
These claims are partially true. However, the science of rock dust reveals that you won’t see the benefits of adding rock dust to your garden within your lifetime. In addition, rock dust is an unnecessary additive, as most soil naturally contains rock dust and other components that balance your garden’s pH, bacteria, and mineral concentration.
So, let’s take a closer look at these claims and check with the science to see if they are true.
Does Rock Dust Add Minerals to Depleted Soil?
Rock dust adds minerals to depleted soil, but plants cannot immediately absorb or interact with the minerals in rock dust. Rock dust must decompose before releasing these minerals into your garden, and decomposition can take 100 years or more.
The trace minerals and elements that plants need in their soil include
- Boron
- Copper
- Iron
- Manganese
- Molybdenum
- Zinc
- Calcium
- Sulfur
Plants may need other minerals to thrive, including silicon, selenium, iodine, and cobalt. However, scientific studies have not shown whether these additional elements affect plant growth.
Rock dust, which includes around 67 trace elements and minerals, contains all the nutrients plants need. However, the chemical composition of rocks makes these nutrients inaccessible to plants.
Rocks are dense deposits of minerals and other solid elements that have compressed and compacted over thousands, if not millions, of years. When you grind a stone to make rock dust, the chemical composition does not change – rocks are still durable and resistant to weather and decay, even when powdered.
Since most rocks don’t readily dissolve in water or dirt, adding rock dust to your garden will not deliver soluble nutrients to your plants or the bacteria in your soil. All the rock’s “building blocks” will be there, but they can’t directly offer your vegetation any easy food.
So, in summary, rock dust adds minerals and other elements to your garden. However, because rocks are so rigid and resist decomposition, your plants won’t be able to use these minerals. In this regard, rock dust won’t help your plants grow.
For more information on why rock dust isn’t necessary for your garden, check out this video from Simplify Gardening:
Does Rock Dust Raise Your Soil’s pH?
Rock dust does not raise your soil’s pH immediately because it is insoluble. The dust will have to decompose and become soluble before affecting your garden’s pH or nutrient contents. This process can take many years.
So, although the elements inside rock dust have a neutral pH ideal for balancing your soil’s alkalinity, these components are inaccessible to your soil and have little to no effect on your garden.
In this case, the insolubility of rock dust again undermines the claims that it can balance your soil’s pH. However, since rock dust will eventually decompose, it can adjust your soil’s alkalinity – but only if you are willing to wait 50 to 100 years to see the effects.
However, I must mention two caveats – lime and gypsum. These soluble rock materials can lower or raise your soil’s pH immediately. However, they are not technically “rock dust” (genuine rock dust only includes basalt, granite, glacial dust, and azomite).
There are plenty of other pH-balancing options for most gardeners that take immediate effect.
Does Rock Dust Encourage Healthy Bacterial Growth in Soil?
Rock dust encourages healthy bacterial growth once the dust becomes soluble and decomposes. However, adding rock dust may decrease aeration and drainage initially, leading to the development of anaerobic bacterial and fungal growth.
Like the other claims, rock dust only has beneficial effects for gardening once it decomposes. When it becomes soluble and balances the soil pH, it will also facilitate healthy bacterial growth.
However, fine-grit rock dust has adverse effects on gardens before breaking down. Using rock dust is like adding sand or chalk to your garden. It can quickly compact, become soggy, and cake to decrease aeration and introduce side effects, including root rot and anaerobic bacterial and fungal growth.
The Bottom Line: Does Rock Dust Actually Work For Gardening?
Rock dust doesn’t actually work for gardening when making short-term soil amendments or fertilizing. According to scientific research and soil amendment trials, the minerals in rock dust are soluble until they decompose. So, adding rock dust to your garden has few immediate benefits.
Although adding rock dust to your soil will not immediately remineralize your soil, it will benefit natural soils in the long term. So, don’t add rock dust to your garden if you want to boost up this year’s crop. Add rock dust if you wish to naturally enrich your soil, and only expect to see results in the next 50 to 100 years.
Rock dust has a right to claim that it will remineralize your soil, neutralize the pH, and encourage healthy bacterial growth, but it will only do these things after a very long waiting period. Likewise, adding too much rock dust to a garden can restrict aeration and drainage, so to improve the dirt, you will have to sprinkle a bit of dust every year for quite a few years.
So in practice, rock dust is a beneficial product if you use it frequently and in small quantities over a very long period. For most people, that’s way too much maintenance. If that describes you, you’d be better off picking a proper NPK fertilizer and adding amendments like lime or gypsum.
Last but not least, rock dust is just as effective as adding raw stones to your garden. So, you don’t have to shell out money to purchase rock dust. If you are interested in reaping the benefits of rock dust, toss a few stones in your garden and wait.
Conclusion
Rock dust has received much hype in the past few years since it claims to remineralize and balance your soil organically. However, what’s not included in the product description is that you will have to wait many years to see these benefits. Rocks take a long time to decompose, and the minerals inside rock dust are only beneficial to plants once they become soluble.
So, if you need a quick fix to your garden’s soil, opt for fertilizer and mineral additives. It’ll save you about a century of waiting.
If you want to learn more about improving soil quality, you can read my other article here: How to Improve Soil Quality (The Ultimate Guide)
