Gravel versus sand is one of the oldest debates in the aquarium hobby. Just to let you know right off the bat: neither one is better than the other. Both gravel and sand have specific advantages and disadvantages that make them great choices. But how do they compare when choosing a substrate for live plants? Can you keep aquarium plants in gravel?
What Are the Pros of Keeping Aquarium Plants in Gravel?
Here are a few of the benefits of keeping your plants in a gravel substrate:
Water Flow & Compaction
Aquarium gravel is much better than sand when it comes to allowing water to flow and preventing substrate compaction. Adequate water flow through the substrate is very important.
It ensures plant roots have access to both carbon dioxide and oxygen as needed. Any fertilizers you add straight into the water column may not entirely reach the roots if you’re using a thick sand substrate.
Most plants also uptake nutrients through their leaves and stems but this amount varies depending on the species. Some, including Amazon Sword plants, prefer to feed through their roots.
Good water flow through your gravel helps wick away waste products as well. If organic debris trapped inside begins to rot, there’s plenty of oxygen at hand for aerobic (oxygen-loving) bacteria to break things down.
Sand, on the other hand, occasionally has issues with anaerobic pockets forming. It’s typically not an issue unless your sand substrate is more than 2-3 inches in depth and there are no burrowing animals or plant roots to aerate it.
If thick beds of sand aren’t shifted about they can get compacted. Once organic matter gets trapped deep inside the compacted sand, anaerobic (oxygen-hating) bacteria can get a hold of it.
The waste products they release are especially toxic. They prevent plant root growth in their immediate vicinity and if the pocket is suddenly disturbed it can burp out noxious gases in lethal quantities.
Debris Collection
The ability of gravel to allow water to flow through it also helps leftover food, fish waste, and other undesirable bits remain hidden! They fall in between the grains rather than sitting on the surface the way they do with sand.
Leftover food and fish waste will rot eventually, though. So you’ll need to make sure you use a good gravel vacuum to turn over the gravel bed to get all of the waste that’s fallen deep within.
A lot of this organic waste also contains nutrients like phosphorus, nitrogen, and potassium, all of which are essential to plants. Since gravel isn’t nutritious on its own, it’s important to consider how your plants are going to get fed.
Not all plants need fertilizer and not all aquarists want to use it. However if you’re planning to rely on your fish to provide the nutrients plants need, gravel is a much better bet than sand unless you’re using sand that can store nutrients.
We’ll talk more about CEC (cation exchange capacity) and how it helps aquarium plants thrive later!
Appearance
This last point can go in either direction. Gravel has a delightful rubble-like appearance and even naturally shaded gravel tends to be multicolored. Sand has a very uniform look that may not work with the aquascape you have in mind.
Gravel mixes more naturally with rocks as well. It creates the appearance of weathering and erosion in Nature-style aquascapes that sand doesn’t always match.
What Are the Cons of Keeping Aquarium Plants in Gravel?
Here are a few of the drawbacks of using a gravel substrate with plants:
Plant Anchoring Capacity
This is actually a mixed bag because some plants root better in gravel versus sand. Once sand has had a chance to settle it’s usually a slightly better substrate. However if your plants are being buffeted by current from your filter, strong roots in gravel can help them hold fast.
Thick-rooted plants like Cryptocoryne and Amazon Sword Plants often root better in gravel. Plants with finer root structures are better off in sand. The space between gravel grains may not be tight enough to hold them in place.
Nutrient Collection & Storage Capacity
Inert gravel is made mostly of crushed rock. Inert sand is too, but once nutrients do make it into the spaces between the grains it doesn’t leave so quickly.
Remember how I mentioned that the water flow of gravel was a benefit? Well, the downside is that nutrients may not stay in place once they flow into the substrate.
In nature, there’s rarely ever spots where you have uniform patches of sand or gravel. You almost always see a mixture of grains of all sizes. This ensures wild plants get the best of both sand and gravel.
In fact, I recommend mixing sand and gravel for this very reason in planted tanks! Not only is it beneficial but it looks even more natural than a big expanse of evenly sized rubble.
If you’re looking to improve the nutrient collection and storage capacity of your gravel, go with an aquarium plant substrate. Several of these are gravel-sized, including Eco-Complete and Seachem Flourite.
However they are made of porous volcanic rock and fractured clay chunks that can fit nutrient molecules within their structure. Their high CEC (cation exchange capacity) ensures they act as an organic sponge for plant nutrients!
Plain gravel can also be enriched using fertilizer tablets. These can be buried within the gravel near plant roots. As the tablets get wet they slow-release nutrients over the course of weeks or months directly to the plant’s roots. Plant fertilizer tablets can allow you to skip aquatic fertilizer doses entirely!
Burrowing Animals
Many aquarists forget that fish don’t always swim in the water column. Some species prefer to root about and even submerge themselves in the substrate, hiding from view entirely! However this habit can be a real problem if you keep your aquarium plants in gravel.
There are many burrowing animals out there, including Stingrays, Assassin Snails, Kuhli Loaches, and Spiny Eels. Any of the smaller species could do well with established plants that are hard to uproot.
However nearly all burrowing fish are scaleless. This means they have soft, skin-covered sides that are very easily scratched by the sharp edges of gravel grains.
These wounds can easily get infected, eventually leading to death. Sand is a much better choice if you have fish or invertebrates that love digging.
On the plus side, if you don’t want animals doing landscaping then gravel is actually a better choice than sand. Cichlids, Crayfish, and other diggers have a harder time hauling large gravel grains about compared to finer sand.
Your gravel will likely be moved eventually since your fish are going to be persistent and really have nothing better to do. But the holes and piles will be much smaller compared to a sand substrate!
Conclusion
When it comes to sand versus gravel for aquarium plants there is no simple answer. As it turns out, both sand and gravel are excellent choices for plants that have unique benefits.
Gravel is great if you have plants with large roots, rocky aquascapes, no burrowing animals, and want debris and fertilizers to directly reach plant roots. It’s also a great aesthetic choice if you don’t want the uniform expanse of a patch of sand!
