Calathea plants, known for their strikingly patterned foliage and unique leaf movements, are popular tropical houseplants. These “prayer plants” thrive in environments that mimic the warm, humid conditions of their native rainforest understory. Growing Calathea in water, known as water culture or hydroponics, appeals to many enthusiasts seeking an alternative to traditional soil. Successful long-term cultivation in water requires a precise understanding of the plant’s root structure and specialized environmental management.
Rooting Calathea Divisions in Water
Unlike many common houseplants that propagate easily from stem cuttings, Calatheas are rhizomatous plants that grow from underground stems. Creating new plants typically involves separating the root ball into smaller clumps, a process called division. This method is more reliable because the new individuals already possess their own root systems.
Water is primarily used as a temporary rooting medium rather than a permanent home for the division. A healthy clump should be gently separated from the mother plant, ensuring each section retains existing roots and rhizomes. After separation, carefully rinse away the original potting soil to prevent contaminants from fouling the water.
The cleaned division is placed into a vessel with water, ensuring the water level covers the roots and rhizomes entirely. During this temporary phase, the water must be replaced frequently, ideally once a week, to maintain oxygen levels and prevent rot caused by anaerobic bacteria. This initial water rooting encourages the development of water-adapted roots, which are necessary for a permanent transition.
The Transition to Long-Term Water Culture
Moving a Calathea from soil to a permanent water-based system presents several challenges, primarily centered on root oxygenation. Soil-developed roots draw oxygen from air pockets and quickly suffocate when fully submerged in stagnant water, leading to rot and plant decline. To prevent this, soil-grown roots must be meticulously cleaned or allowed to rot away and be replaced by new, water-adapted roots, which can take several weeks.
For sustained growth in pure water, environmental conditions must be carefully controlled. The vessel should ideally be opaque or dark to prevent light from reaching the water, which inhibits algae growth. Algae compete with the plant for nutrients and oxygen. Furthermore, the water temperature must remain stable, as fluctuations can stress the sensitive root system.
Many growers find greater long-term success by adopting a semi-hydroponic approach, commonly using Lightweight Expanded Clay Aggregate (LECA) or similar porous materials like pumice. This medium provides physical support while allowing a reservoir of water and nutrients at the bottom of the container. The clay pebbles wick moisture upward, keeping the roots consistently damp. The numerous air gaps between the pellets ensure sufficient oxygen flow, which is often the missing element in full water culture. In a semi-hydro setup, the water level is typically maintained one to two centimeters below the base of the roots to encourage healthy respiration.
Essential Nutrient Requirements for Water-Grown Calathea
Plants grown in water cannot access the mineral nutrients typically provided by soil, making a specialized nutrient solution necessary. Standard houseplant fertilizers are unsuitable because they lack the complete range of micronutrients and can quickly create toxic salt build-up in a contained water system. Instead, a balanced hydroponic-specific solution must be used, containing the complete profile of macro and micronutrients, including nitrogen, phosphorus, potassium, calcium, and iron.
Calatheas are sensitive and require a much lower concentration of nutrients than many other hydroponically grown plants. The strength of the solution is measured by its Electrical Conductivity (EC), which indicates the total concentration of dissolved salts. While the general hydroponic range is 0.8 to 2.5 mS/cm, Calatheas often thrive at the lower end of this spectrum, or even at a quarter-strength dilution.
The pH of the solution is equally important, as it determines the availability of nutrients for root uptake. For Calatheas, the nutrient solution should be maintained within a slightly acidic range, ideally between pH 5.5 and 6.5, which optimizes the absorption of necessary elements. Regular monitoring of both EC and pH is required, and the solution must be completely refreshed at least every two weeks or monthly to prevent the build-up of mineral salts and contaminants.