With Hydroponics, the soil is subtracted from the equation to be replaced by nutrient-rich water. The roots are generally embedded in a support medium, like Rockwool, expanded clay, or perlite and the nutrients are provided either by a drip or an ebb and flow system.
These support mediums are widely used and have varied price ranges, advantages, and disadvantages. Part of their role is to support the plants themselves, aid in nutrient absorption and water retention, and assist in controlling the overall environment so that there are no ph fluctuations outside the accepted ranges in this enclosed ecosphere.
In the end, they can influence factors such as whether there will be a mediocre yield or an abundant harvest.
One media that is often overlooked is gravel. It is not the first choice of many a hydro culturist but it has many advantages, mainly its cost-effectiveness, ready availability, and its durability. Just for those reasons alone many hydroponic growers believe it is worth using as a substrate.
Gravel Advantages and Disadvantages for Hydroponics
The preferred support medium to use in hydroponics is one that does not absorb water, is ph neutral, is reusable, and provides good aeration. Gravel ticks all these boxes and then some, coming in a wide variety of shapes and sizes.
Gravel for hydroponics generally falls into two categories, “sharp” gravel or “pea” gravel, and whichever is chosen can sometimes just be a matter of preference. However, whatever type of gravel is chosen it is advisable to wash thoroughly to eliminate any debris, dust, or dirt particles that can perhaps clog any pumps used.
The distinction between the two is that one is rounded and the other has sharp edges, and a mixture of the two is ideally suited for use as a substrate, generally a mixture of 3/8 to 5/8.
This screening mixture allows particles to filter through and pass their nutrients onto the hanging roots. If the gravel is too densely packed, it would prohibit the free flow of nutrients to the plants and literally starve the crops to death.
What the sharper pieces of gravel tend to do is hold on to nutrients as they flow over the surface areas. This is important because minute particles of nutrients become trapped between the small jagged crevices, and in between the irrigation, the cycle helps to sustain the plants.
Apart from that the rougher surface also provides the roots a better ability to anchor to for stability, where a smoother rock would not, and also the rougher surfaces stop the gravel itself from shifting whenever the water is flowing through and around it.
Occasionally the gravel itself will become soiled and need to be cleaned. Fortunately, unlike some other substrates which have to be thrown out and replaced, gravel can be extracted from the grow bed after harvesting, and any unwanted material that is adhering to surfaces can be washed free. Once free of any dead roots or debris, the now cleaned and sterilized gravel can be put back into position for the next planting session.
This process can be repeated indefinitely, saving a lot of time, money, and effort in transporting the aggregate from the store.
As you can imagine the weight of the gravel can be a disadvantage in transportation and installation and that will reflect in the structural considerations for the hydroponic setup.
Whatever planting structure is used to house the substrate and the hydroponics farm, has to be capable of supporting the weight of the gravel over a long period of time, as well as the weight of the water that also has to be factored into the weight baring equation.
See also: What size gravel is best for aquaponics?
Gravel In Hydroponics And The pH Level
The ph level in both hydroponics and aquaponics is constantly requiring recalibration and monitoring to maintain the narrow range. This chemical reaction can occur depending on the type of gravel rock used and that can affect the ph level, raising it higher than the accepted range. If that happens it can interfere with the nutrient absorption as the water flows throughout the system, and adversely affect the plants.
Whether the water is alkaline or acidic can also play a major role in the ph stability ranges and how the gravel will interact within this biosystem. If the water has too much alkalinity, the ph levels can be difficult to stabilize even with the proper equipment and can work out to be a costly endeavor trying to maintain the equilibrium.
On the other hand, too acidic a water source can be aided by the gravel which will actually correct the imbalance.
So, it pays to understand the type of water that is going to be used first in the hydroponic system in regards to its natural ph ratio, as that will help to decide the type of gravel to be selected to avoid any future problems.
Being nonporous, gravel does not have the ability to hold on to water itself. With a drip irrigation system that is not a problem as there is a fairly constant supply of water. However, if using the flood and drain method a back-up system may be required in case of a power cut, or one of the pipes becoming blocked.
And for this reason, with the use of gravel, the watering cycle needs to be more frequent or the roots will dry out and eventually die.
Another item of note to pay attention to is the depth of the gravel which can play a crucial role in the development of the roots. If the gravel is too shallow the roots will not be properly supported and anchored, which in turn will affect the root growing capacity.
If the gravel is too shallow there is also a risk that a layer of algae can form along the surface area which will attract fungi gnats that will revel in feasting on the roots of the crops.
Having a depth of at least 50mm will eliminate this potential build-up as light cannot penetrate to that depth and interact with the moisture to allow the algae to flourish.
The Gravel Truth in Hydroponics
Using gravel as a support medium is ideally suited to an ebb and flow watering system where the aggregate is watered several times a day. It does not absorb nor hold onto the water but its cost-effectiveness and the ability to source it locally offset this disadvantage.
It is important to note that the gravel selected needs to be chemically inert so does not alter the ph level unduly in the ecosystem, so limestone should be avoided. There’s nothing worse than opting for a cheaper support medium only to be committed to doing twice the work in constantly having to recalibrate the ph levels.
Growing crops hydroponically may be a soil-less endeavor but the gravel truth is that it could be the start of a new revolution in sustainable growing, ushering in a new way to feed the world.
And at the end of the day who wouldn’t want to be able to grow more food, faster, and in a completely controlled environment?