Are you wondering if you can plant a cactus exclusively in gravel? I thought about that too back when I first started growing cactus professionally a few years ago.
Cactus planted in pure gravel will have a short life span due to the gravel’s lack of essential nutrients and water retention capability needed for cactus to survive. However, incorporating organic materials and fertilizers into the gravel medium coupled with regular watering can prolong the plant’s life.
Cactus prefers a substrate that doesn’t hold too much water. While gravel can be an option, using them as a pure growing medium has drawbacks. Here’s a brief rundown about planting cactus in gravel.
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Gravel is a type of rock in various sizes (2-80mm) and textures widely used in the gardening world and not only. In geology, gravel is a smooth and rounded natural aggregate derived from bedrock weathering and deposited through water transport.
U.S. Geological Survey distinguished gravel from crushed stones, an aggregate of the same size range but with jagged edges resulting from crushing. However, most people in the United States used the term “gravel” to “crushed stone” and “gravel” alike.
The difference between gravel and crushed stones is their texture. Gravels are smooth-edged, while crushed stones have jagged edges.
Pea- gravel and river gravel are two common types of stone used in gardening. Pea gravels have many uses in landscaping, walkways, and fish tanks. River gravel, on the other hand, is smoother and larger than pea gravel. It is typically used in the garden for aesthetic purposes.
Yes, cactus can grow in pure gravel— however, they will not last long. Gravels alone as a growing medium cannot sustain cactus growth as they do not provide the nutrients needed by the plant to survive.
Cactus developed adaptive abilities that allow them to grow in adverse conditions. Some cactus survive in arid conditions due to their ability to store adequate water that makes them drought-tolerant. While most cactus can be this tough, they can’t thrive in gravel substrate alone.
Cactus require certain nutrients and trace minerals to thrive. But neither can be found in gravel, which is mineral-bound and doesn’t provide nutrients. Gravels also tend to dry quickly and may result in dehydrated cactus.
While gravel is an excellent way to provide aeration and drainage for the cactus, it will be devoid of crucial nutrients. For cactus to thrive and last longer, its growing medium must contain soil and other organic or inorganic matters as a source of their nutritional wealth.
Cactus cannot survive longer on gravel medium. But some cacti in the wild are seen to grow on massive rocks.
Did you know that biologists found cactus growing on bare rocks in the volcanic region of Baja, Mexico? The massive cardon cacti, scientifically known as Pachycereus pringlei, are discovered growing on sheer rocks. They are not only thriving but also drilling their massive roots into the rock for anchorage.
Here, a cactus in the wild growing on sheer rocks.
Dr. Yoav Bashan, along with some biologists at Northwestern Center for Biological Research in La Paz, Mexico, discovered many Pachycereus pringlei as they were working in a desert. Pachycereus pringlei thrive on pure rocks. These cardon cactus were looking beautiful and green in places where plants don’t often thrive.
How can these cacti grow on rocks while the majority cannot?
These cacti can eat rocks! These rock-growing cactus have a symbiotic relationship with the microorganism found on their roots, stem tissues, and seeds. The endophytic bacteria dissolve the rock, providing nutrients for cactus needs. In exchange, the cactus enables bacteria to dwell in its roots, providing them with water and carbon.
Some cactus sold commercially in the mall are often planted in gravel. Also, cactus arrangements in glass terrariums use gravels as a planting medium.
There are beautiful commercial cacti planted creatively in gravels. If you have ever seen these, you may wonder why they survived the setup. The cactus arrangements you found in stores and malls are only short-term setups. They are not designed to stay like that for long because they may die.
Gravels are used for aesthetic purposes only to draw the buyer’s attention. Some terrariums have soil on the bottom and gravels as a top dressing only. For this, cactus can grow a bit longer compared to pure gravel medium.
Gravels can make cactus appear well structured and artsy. Incorporating gravels in the cactus arrangement is appealing since it portrays a mini desert look. This makes sense only if gravel is used as a decoration on top of the soi.
However, the use of pure gravel as the only cactus medium has a significant drawback such as:
- A gravel medium does not provide nutrients for the plant. Over time the plant will become unhealthy and will eventually die.
- The cactus will require constant watering and feeding. It will be burdensome and expensive.
- In some cases, the cactus may survive in this condition, but it won’t last long. You’ll end up wasting your beautiful plant.
Yes, cactus can survive without soil. Cactus can grow on mixtures of an organic and inorganic medium that contains nutrients essential for their growth.
Coco peat, carbonized rice hulls, and vermicast are nutrient-rich organic materials usually incorporated with other inorganic substances such as perlite, pumice, and sand to make a soilless medium ideal for cactus.
It may not be suitable for cactus to grow in a gravel medium, but adding nutrient-rich substances will let them thrive and live longer. However, it will require several materials and extra effort.
Cactus potted in gravel medium can survive when supplied with adequate nutrients. Since gravel alone cannot nourish your plant, you have to incorporate fertilizers into your medium.
You may add organic materials like worm castings and carbonized rice hulls. These materials are fortified with nitrogen, phosphorus, potassium, and good microorganisms. Coco coir or peat moss such as the ones below works best as it contains potassium and other trace elements suitable for the cactus.
Feeding your plant with a dash of fertilizers will equip them with total nutritional value. There are several types of fertilizer suitable for your cactus. The commonly used plant foods are osmocote slow-release pellets and liquid fertilizer. I recommend the products below because they work magically and keep my cactus collection well-conditioned.
Another essential factor is your watering schedule. Since gravel tends to dry fast, you need to supply a regular and adequate amount of water to hydrate your plant. Be mindful when watering your cactus. Excess moisture can cause them to rot, while lack of water will cause them to shrink. Both can be detrimental to your plant.
- While gravel can be an excellent way to provide a well-draining medium, it is not an ideal growing medium for cactus.
- Cactus in the wild can grow in massive bedrocks with the aid of microorganisms called endophytic bacteria. The cactus and bacteria develop a symbiotic relationship.
- Cactus can grow in gravel, but without additional nutrient-rich material, they won’t live long.
“Natural Aggregates of the Conterminous United States,” by William H. Langer U.S. Geological Survey
“Rock-degrading endophytic bacteria in cacti,” by M. Esther Puente, Ching Y. Li and Yoav Bashan, Academia Education
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