What’s Better for Water Gardens: Growstones Or Clay Pebbles?


A few days ago, a cousin told me she was planning on renovating her backyard space and wanted to create something pretty and sustainable there. I suggested having a water garden, but she told me she didn’t know how she would go about it. What kind of soil would she use, or soil substitute? So I did some research for her and found out quite a bit about soilless mediums- growstones and clay pebbles..

So, what’s better for water gardens: growstones or clay pebbles? Observation shows that growstones are more beneficial for plants in water gardens than clay pebbles. Growstones support roots by providing maximum aeration and help roots in adhering to them. Growstones are also a more sustainable material.

Water gardens and materials or processes that are used to create and care for such gardens come under hydroponics, a gardening system that encourages growth of plants without soil. Both clay pebbles and growstones are used worldwide for such gardens, but the merits of both have been considered and debated as to which is the better alternative.

What is a water garden?

Water gardens are very often pond-based, and are always considered aquatic gardens since they only house aquatic plants and are solely based on water. Water gardens are quite shallow in depth as aquatic plants can only thrive at a certain depth due to their distinct root systems. Gardening enthusiasts enjoy water gardens for their aesthetic beauty and for aquatic plants that help purify the air, but many serious gardeners also like growing certain crops and vegetables in such spaces as well.

Hydroponic systems in water gardens are becoming an increasingly popular choice for gardening enthusiasts as they are highly sustainable, interesting to create, and have many benefits. Since the water garden is a closed enclosure with generally limited water content, soilless media such as growstones are beneficial, as they help in reducing the amount of water that would otherwise be soaked up by soil. The soilless media also creates a lightweight system which enables the plants to grow in a healthy manner. Even in soilless media, various substrates have been compared to assess which is the best in terms of quality and features provided, and these days more people are moving towards environmentally sustainable yet long lasting options for the same. Hence, for an optimum soilless planting medium, it is questioned whether growstones are better or clay pebbles.

Growstones vs. Clay Pebbles

Growstone is a product created by the eponymous company, Growstone, aiming to provide a sustainable and easy to use alternative soil substrate for hydroponic systems and aquatic gardens. Growstones are made of recycled glass and offer high water retention as well as air retention, which make them highly suited to being used in water gardens. Ground glass is used to form growstones and this has been proven as a better alternative to other media like perlite, peat and parboiled rice hulls, which are also commonly used in hydroponics.

Clay pebbles are, as the name states, made of clay fired in a kiln, which leads to the expansion of the clay pebbles or pellets. Clay pebbles are used widely as they are reusable and it is easy for plants to be pulled out or moved from place when clay pebbles are used. Thus, when you want to replant something, the use of clay pebbles for potting, make the process easier.

It has been understood that growstones are much more beneficial in the long run than clay pebbles, for water gardens. These are some of the main reasons why it is thought so-

  • Clay pebbles are after all made of raw clay, and even though they are baked for a long duration in kilns, over time, in aquatic gardens, they tend to erode and particles come loose from them. This reduces the plants’ ability to hold on with their roots and can damage them. However, growstones are made of ground glass and hence do not erode or break down. Hence, plants and their roots are also protected by the use of growstones.
  • Due to their tendency to break down and erode, clay pebbles also create blockage in drains and filters, which can also spread dirt and mud in the water of the aquatic garden. This takes away the aesthetic value of the garden and will also create clogging and stagnancy in the pond/ aquatic space. Growstones on the other hand, do not tend to cause any blockage and can keep the water garden fresh and clean.
  • Clay pebbles have very low capacity to hold and retain water. While water holding capacity is not a major criterion for most water garden owners, unless it is water-needy crops that are being grown, many do prefer to have a soilless medium that can retain water. This is preferred so that the plants don’t have to be watered too frequently. Since clay pebbles don’t have much water holding capacity, this makes them a less useful option for such preferences. Growstones, however, have the capacity to hold 3 times the water content that clay pebbles can. Hence, they are the preferred option.
  • For a soil substrate to be beneficial for the aquatic plants, it needs to have ample number of air-filled pores, so that enough exchange of gases between the plant and the environment is allowed. Clay pebbles do not have many air-filled pores, which can make it difficult for plants to exchange gases. Growstones, on the other hand have a high number of such pores and have been observed to facilitate the gas exchange by about 25% more as compared to other media like perlite as well.
  • For smaller aquatic systems, and in the short run, clay pebbles may be a viable option, but growstones are not only sustainable, they also cost less when purchased in bulk. Additionally, growstones are non-toxic, so it also guarantees safer and more sustainable use. Although clay pebbles are also reusable, their tendency to erode makes them a less sustainable and hence less renewable option. Clay pebbles are also known to be strip-mined, and strip mining has negative consequences for the environment, hence making them a less sustainable option. Since water gardens are themselves largely sustainable, it’s a good thought to use corresponding material in them as well.
  • Growstones are made of ground glass powder and is hence very lightweight. Not only is it easy to carry around in big quantities, it also holds down the plants in the water garden without weighing them down. However, clay pebbles are known to be rather dense and heavy weight in comparison and hence are not preferred to growstones. Particularly in ebb and flow systems, the clay pebbles can get very weighty. Growstones are just lightweight enough to support the plants without dragging them under, but heavy enough to stay in place and support the roots, which makes them a perfect option.
  • Clay pebbles come with a time-consuming cleaning process. Before putting the clay pebbles in the water garden bed, the clay pebbles have to be washed thoroughly.  Many times, the cleaning process involves using alcohol based cleaners to detoxify the pebbles, and the process can be tiresome. Moreover, clay pebbles release a lot of reddish dust, which can make things messy and can also spread in the water of the garden. Clay pebbles also have to be cleaned from time to time during use, which is an additional hassle. Growstones are better for the aquatic garden environment as they don’t need to be cleaned frequently and release no dust.
  • Clay pebbles don’t provide nutrients to plants by usage, and in a water garden, it becomes important for the gardener to provide as much external nutrition to the plants, which don’t have a soil medium to gather nutrients from. In comparison, growstones also do not provide nutrients to aquatic plants, but they do allow more scope for nutrients to pass through to the plants and help them in retaining said nutrients much better than clay pebbles.
  • Despite being lightweight, growstones are able to hold plants by the roots, in their places such that they cannot be swept away in the water. Growstones allow plant roots to take hold firmly and strongly, which is important in a hydroponic water garden system. On the other hand, clay pebbles make it very easy for plants to be moved around, which could be a negative, considering that it is an aquatic system and one would not want plants to be moved without human effort.
  • Hydroton such as clay pebbles are known to change the pH balance of soil and in case it is itself the soil substrate, such a medium can upset the pH balance of nutrients taken in by the plant. It is important to remember that this is a soilless system in a water garden, so pH balance is necessary to ensure that the plants thrive. However, growstones are better in this regard as they do not cause change in the existing pH and by using growstones, the pH control is in your hands alone.
  • In case the water garden has drip-style watering system in place, clay pebbles are not a great option as they will suck in all the hydration and in the attempt to provide adequate water to the plants, you may end up underwatering or overwatering them. It is hard to find a balance in watering properly when clay pebbles are used, particularly for aquatic plants, many of which are delicate. Growstones do not interfere that way with the water level and are hence more suitable.
  • Clay pebbles generally have specific use, as they form replacement of soil in potting and in gardens, but growstones can also be used to supplement purely aesthetic purposes. If one has some decorative plants in the water garden, growstones can be used to form a bed for these plants and will have no side effects such as releasing dust, requiring washing, like clay pebbles are prone to.
  • Another downside to clay pebbles is that they dry out very fast. This can be a disadvantage particularly in hotter and drier climates where one wants to grow a water garden. In this case, the plants can dry out from the roots due to the use of clay pebbles and will wither. However, there is no such danger with growstones as they can retain and release moisture adequately as per the aquatic plants’ needs.

Thus, it is evident that growstones make a much more useful and viable soilless substrate for water gardens. To sum it up, it can be stated that growstones are superior to clay pebbles in several ways as they provide more aeration to the aquatic plants, are lightweight, highly sustainable, have enough water retention capacity, and can be reused several times without any of the hassles clay pebbles come with. That being said, many gardeners find growstones expensive in comparison, and wish to stick to clay pebbles.

However, in the long run, growstones provide a higher number of uses and are often cost-effective when purchased in bulk quantities. Growstones are also a good medium as the ground glass they are made of is almost always recycled, which eliminates another environmental concern. For water gardens, growstones are great as they form the perfect balance between water retention and release.

Why growstones are considered superior to other substrates

Not just in case of clay pebbles, growstones are also considered a better substrate than other options available, Perlite, for instance, was a widely popular option for soilless systems and even now continues to be used by many where it is readily available. Perlite is basically volcanic glass that has the ability to expand when heated and can hold good quantities of water. Perlite also has good drainage capacity and provides adequate aeration to plants, an important feature for aquatic plants in a soilless system.

However, it has been observed that growstones have higher water and air retention abilities than perlite Perlite’s lightweight texture, while useful in hydroponic systems, turned out to be too lightweight, such that much of it can be washed away by water movement, whereas growstones show no such issue. Moreover, perlite contains some toxins that can be harmful in the long run to those who inhale it while using it, which makes growstones a winner again.

Sure To Grow was another popular product as it offered a firm base for plants to cling on to, and thus created an integrated hydroponic system, something which would be useful in a water garden. However, growstones managed to beat Sure To Grow as well, as the latter turned out to be fairly expensive, was made of plastic, and was not reusable. Meanwhile, growstones are made of ground glass which is always recycled, is reusable plenty of times, and is hence more sustainable an option.

Inexpensive options such as brick shards, polystyrene packing peanuts and wood fiber have also been used, but these all come with disadvantages that outweigh the benefits. Brick shards can severely affect the pH balance of the medium, while packing peanuts can release styrene which the plants may take in. Wood fiber has the risk of lacking sterility and attracting unwanted insects, which would be a mess in a water garden. Thus, these options do not stand very well in front of growstones.

Coconut coir, more commonly known as coco coir, is becoming an increasingly popular soil substrate option among gardening enthusiasts. Coco coir is great for hydroponic systems and water-based systems as well since it has good air flow and air and water retention capacity, provides a base full of hormones and free from harmful viruses for the aquatic plants, and is a very eco-friendly, sustainable choice. It is also cost-effective.

However, the major issue with coco coir in a water garden would be that it can absorb too much water due to the already high amount of water in the garden itself and this can weigh the plants down. As aquatic plants are often delicate with roots that are not naturally strong, using coco coir could lead to the plants drowning in the water garden. However, these days, many gardeners are using coco coir in tandem with media such as growstones to make the best of both worlds- combining growstone’s lightweight aeration qualities and strength with coco coir’s nutrient rich system.

Related Questions

What plants can be grown easily in a water garden?

Aquatic plants can require a little patience and care, but once at a certain level, can sustain themselves well. Good options are hornwort, water lettuce, pitcher plant, rain lilies, sweet flag, and if you’re looking for something particularly pretty: Japanese primrose for the edge of the water garden.

Are growstones suited and available only for hydroponic systems?

The best thing about growstones is that the company offers a range of growstone varieties for different uses- GS-1 to be used as a soil substrate in hydroponic system, GS-2 as a mix to increase aeration, GS-3 for swift drainage, a mix containing coco coir, GS-4 for retaining water, and Growstone Gnat-Nix.     

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