Hydroponics is the art of growing plants without soil. It has been gaining popularity among gardeners and farmers alike. One of the most common materials used in hydroponics is rockwool. However, despite its popularity, there are several reasons why you might want to reconsider using rockwool in your hydroponic system. Now, these are my personal reasons based on my KISS approach as I try to pursue simplicity, affordability and efficiency in my own hydroponics. I know you’ll find others who swear rockwool provides a better experience in their hydroponics systems. so do your own research and make the best decision for your hydroponics garden.
Rockwool Is Difficult to Reuse and Recycle
This is my main issue, because I started off, like most hydroponics gardeners do, by following the popular recommended choice of using rockwool to start my seeds and plant out my hydroponics plants.
The properties of rockwool may be great for hydroponic use: they allow great water absorption. But, once they have been used, I found they are difficult to re-use. Given that they also carry an environmental cost, this is not ideal. Plus, it adds cost- and I am all about keeping it simple and reducing costs wherever possible.
I found getting the plants out, along with roots, left the used rockwool cubes difficult to re-use. In fact, they will often break apart and become unusable. They also can make for great algae production, so need to be cleaned if they are to be re-used. This takes time and effort again. And they don’t all survive in the cleaning process. So, all this time, cost and potential wastage is a major negative for me. And I believe there are better alternatives.
The Environmental Impact of Rockwool
Rockwool is a type of mineral wool made from basalt rock and chalk. While it’s praised for its excellent water retention and aeration properties, its environmental impact is a cause for concern.
Firstly, the production process of rockwool requires a significant amount of energy. The raw materials need to be heated to a staggering 3,000 degrees Fahrenheit to create the fibrous structure that makes rockwool so effective for plant growth. This energy-intensive process contributes to greenhouse gas emissions and global warming.
Secondly, rockwool is not biodegradable. Once it’s used, it can take hundreds of years to break down in the environment. This means that used rockwool often ends up in landfills, contributing to the growing problem of waste management.
The Health Risks Associated with Rockwool
Aside from its environmental impact, rockwool also poses potential health risks. I haven’t experienced this to any significant degree, but have have had some “itchies” from the rock wool!
The fibrous nature of rockwool can cause irritation to the skin, eyes, and respiratory system. This is especially true for people who are exposed to it regularly, such as hydroponic growers.
Moreover, rockwool fibers can become airborne and if inhaled, they can cause serious health problems. Long-term exposure to these fibers has been linked to chronic respiratory diseases. Therefore, it’s recommended to wear protective clothing and a mask when handling rockwool.
Rockwool May Require Preparation
Not everyone will agree on this, but typically, the rockwool cubes will need a treatment. Rockwool has a naturally higher pH level. That’s why many will recommend that the cubes need to soak in a pH neutral solution. This allows the pH of the rock wool to be corrected. Not everyone does this but some folks will recommend that cubes need to be soaked for hours before planting out and others say a few minutes. Either way, you’ll have to figure out what works best for you. I’m about simplicity (and reducing my effort!), so adding other steps isn’t ideal for me.
Rockwool can prove to be costly
There are some ways to reduce the cost. For example, you can buy rockwool slabs and cut them up for yourself. That’s a bit of extra work but can save some significant money. Otherwise, rockwool can be more expensive than other alternatives, especially when you consider they are not easy to reuse or recycle.
Large Plants Can Become Unwieldy in Rockwool Cubes
Rockwool cubes can can be used effectively for germination and younger plants. But, if you are growing larger plants like tomatoes or peppers, or melons and the like, the smaller rockwool cubes will require stabilising. The cubes are small, and plants like tomatoes can grow large, making the entire thing unstable. So, rockwool cubes will need to be secured in a more stable, deeper growing medium. I found using clay balls around the rock wool cubes in a larger net cup helped. You could also use larger segments of rockwool, but that wil probably be a pain and more expensive too. So, if you are using rockwool, smaller plants like lettuce and other leafy greens are a great size, but larger ones will need some stabilising as they grow.
Alternatives to Rockwool in Hydroponics
Given the environmental and health concerns associated with rockwool, many hydroponic growers are looking for alternatives. Fortunately, there are several other materials that can be used in hydroponics that are more sustainable and safer to handle.
Coco Coir
Coco coir, made from the husks of coconuts, is a renewable and biodegradable alternative to rockwool. It has excellent water retention properties and provides good aeration for plant roots. Moreover, it’s pH neutral, which makes it easier to manage in a hydroponic system. By far, this is my grow medium of choice, especially for germination, but also for larger plants, including root vegetables. It’s easy to remove old roots from it and treat it to dissolve any leftover organic material if you need a ultra clean restart. It holds moisture, but I find releases water easier than rockwool- the rockwool cubes may become simply saturated with water, soggy and kind of nasty. Coco is an improvement over that.
Coco coir is also cheaper than rockwool. It works out at least half the cost. So, that is another argument in favor of coco coir vs rockwool.
Peat Moss
Peat moss is another organic material that can be used in hydroponics. It’s highly absorbent and provides a good environment for root growth. However, it’s worth noting that peat moss is not a renewable resource and its extraction can damage peatland ecosystems.
Perlite
Perlite, a type of volcanic glass, is a popular choice for hydroponic growers. It’s lightweight, porous, and provides excellent drainage. However, like rockwool, perlite is not biodegradable and its production is energy-intensive. That said, it makes a great addition to coco coir as a grow medium mix for all kinds of plants like tomatoes, peppers, melons, and even root vegetables. Try growing those plants in rockwool!
Hydroton (Expanded Clay Balls)
Ok, so you may not be able to start your plants off in clay balls (also called hydroton). But, if you are using coco coir for germination and then do need to transplant to another growing medium, expanded clay balls are great. Expanded clay balls can also be reused after some simple cleaning. So, they tick my boxes! They may also be helpful for stablising your plant if you do use rockwool cubes.
The Bottom Line on Rockwool
Rockwool may be familiar as an insulation material. But it is also extremely popular in gardening. It’s absorbent and aeration properties make it suitable for hydroponics use where adequate oxygen and nutrient uptake are crucial. While rockwool has its advantages in hydroponic systems, its environmental impact and potential health risks make it a less desirable choice. There are several other materials available that can provide similar benefits without the downsides of rockwool. As hydroponic growers, it’s important to consider not only the growth of our plants but also the impact of our practices on the environment and our health.