What Type of Hydroponics Rock Gravel Should You Use?


A quick google search of images of hydroponics returns laboratory-like images with PVC piping, pumps, and white fluorescent light tubes. This may seem like a daunting task with gadgets required — but it’s really not.  It’s simply an alternative to conventional soil-based gardening by using nutrient-rich water to stimulate growth. Employing such a cultivation method can result in faster plant maturity as well as higher yields, and contrary to popular belief, hydroponics actually use less water when compared to traditional soil-based methods. 

On top of that, there are fewer potential complications that affect the growth of plants; such as weeds, pests, and diseases. As a result, lesser insecticides and herbicides are required, reducing the cost. You’ll find these gardening techniques employed by high-tech agriculture companies that have vertical farms to maximize the use of space, especially in densely populated cities.

That said, soil allows the roots of plants to be grounded, so without it, hydroponics require mediums for the roots to ground itself and support the rest of the plant.

When it comes to selecting the type of medium, it is important to know what are the considerations that take precedence for you. For instance, the cost, the type of system that is going to be used as well as the environmental impacts of the material, just to name a few. Here are the five best mediums for gardeners of any level. 

1. Rock

Yup, just good ol’ rock. Any sort of gravel would work, such as gravel used in aquariums or bigger river rocks. This makes it easily available and inexpensive for people starting out. Furthermore, it is easy to clean and maintain, allowing reusability which keeps long-term costs down.

However, there are several things to note. First, rocks tend to be loosely packed, so it does not retain moisture well. What this means is that roots may dry out quickly. Secondly, rocks can be quite heavy which makes it difficult to transport and cleanout. And lastly, you need to be careful to reduce the rocks’ contact with water as it may cause a pH imbalance. This changes the ratios of nutrients in the solution, resulting in less than desirable results.

All in all, this is a good medium for those who are getting into hydroponics as it is a relatively easy material to work with, especially now that you know what to look out for. With low to no cost at all, this medium is very suitable for newcomers to hydroponics.

2. Coco Coir

As the name suggests, this medium is made of coconut husk. It comes in three forms — pith, fibers, and chips. For starters, Pith looks and feels like soil. It is dense and can retain water very well — but do be careful as it may drown the roots. On the other hand, Fibers look like ropes and that allows for good permeability of oxygen, but it is not very absorbent to hold water. 

As such, chips are seen to be the best of both worlds. These are small chunks of pith that provide the best middle ground for both water retention and oxygen permeability.

Coco coir is able to retain moisture and nutrients while allowing good oxygen flow to the roots. In order to aid in the draining of water, it is recommended that coco coir is mixed with other mediums that drain out easily like expanded clay pellets. It has a neutral pH which makes it easier when balancing the pH of the water and nutrients especially if you are unsure about the type of nutrients that your plants require. 

As a bonus, this is the most environmentally friendly item on this list as it is made of an organic matter, which makes it biodegradable, and it can be used as compost at the end of its plant raising career. Coco coir is best used in drip, aquaponic, ebb and flow systems, so do consider this medium if you’re growing plants like lettuce, tomatoes, and cucumbers.

3. Expanded clay pebbles

Have you ever seen little balls that look like peanuts in potted plants? Well, those are expanded clay pebbles! Though they are certainly not the cheapest, averaging about $20 for a 5L bag, they are incredibly durable. This means that you can reuse and clean it many times, allowing the initial cost to be recouped in the long run. It is both pH and nutrient neutral, making it easy to control. 

Expanded clay pebbles are very porous and loosely packed, which causes water to be drained very quickly. It’s not great for thirsty plants because of the low moisture content, but it can suit certain types of hydroponics systems that require flooding and draining of water. They include drip, ebb and flow, aquaponics systems.

4. Rockwool

Rockwool is the most commonly used medium in hydroponics due to its many benefits. The material retains water well, reducing the chances of underwatering. Yet, it is porous enough for good oxygen flow of the roots which reduces drowning. This combination allows the optimal growth of plants which results in high yields.

While objectively rockwool is a very good medium, note that there are several caveats. Before planting can begin, the rockwool must be soaked in slightly acidic water, which increases the amount of labor required. This is done for two reasons. First, rockwool has a high pH level which has to be balanced so that the plants can grow optimally.

Secondly, the manufacturing process of rockwool produces fine fibers and dust that can cause irritation to the skin, eyes, and lungs. Thus, it is advised that goggles, masks, and gloves are worn when handling a fresh batch of rockwool. Thankfully, rockwool can be reused, and this process only needs to be done once. 

Rockwool is an incredibly versatile medium as it is suitable for use in all systems which makes it a favorite of both enthusiasts and professionals.

5. Oasis Cubes

Oasis cubes are similar to rockwools except they have other distinctive advantages. For one, they are less costly than rockwool. Furthermore, because it already has a neutral pH, the blocks do not need to be soaked before planting can occur. At the same time, oasis cubes still retain good moisture retention and good airflow of rockwools.

The downside to it is that much like rockwool,  oasis cubes are not the most environmentally friendly option when it is produced. It’s not biodegradable, thus contributing to the growing global landfill problem.

Oasis cubes are also less versatile. Due to the lack of fertilizers in the cubes, they are more suitable for the early stages of growth, such as plants in the seeds or stem cuttings stage. It’s likely that you’ll need to perform a transplant during the later stages and change to more nutrient-rich mediums for optimal growth.


Selecting the right medium for your hydroponics project is an important part of the equation, one that you should consider. However, equally crucial is to consider what type of hydroponics system you intend to employ. Finding the right combination of system and medium would not only help you achieve the desired yield but also determine the complexity of setting up and maintaining the system in the long run. 


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