The planted tank: Complete guide to growing underwater plants

Aquatic plants have evolved to thrive in an environment vastly different from their land-based counterparts. Their internal structure features air cavities running from roots to leaf tips, aiding buoyancy. Unlike terrestrial plants, aquatic species have less supportive tissue since water provides natural support.

Sunlight is vital for all plants, including aquatic ones, enabling photosynthesis by absorbing specific wavelengths. While land plants feature a waxy cuticle to prevent drying, aquatic plants have a much thinner layer to facilitate better gas absorption underwater.

Understanding the Science of Aquatic Plant Growth

To grow plants successfully underwater, a few scientific fundamentals must be understood:

1. Photosynthesis: Plants convert carbon dioxide and water into oxygen and energy (stored as sugars) using light. Photosynthesis occurs only under light; after lights out, respiration continues, consuming oxygen and releasing carbon dioxide. This balance means CO2 injection systems should be turned off before lights go out to avoid harming fish.
2. Nutrients: Aquatic plants require essential nutrients such as nitrogen, phosphorus, potassium, and sodium. In aquarium setups, fish waste often provides nitrogen, complemented by fertilisers in the water or substrate to supply other nutrients.
3. Lighting: Adequate light intensity and duration are critical for plant health and photosynthesis. Different plants have different light requirements.
4. Water quality: Water holds less CO2 than air and reduces light transmission compared to open air. Clean tanks might lack sufficient nutrients, making fertilisation necessary.

Not all plants marketed for aquariums are fully aquatic. Submersed plants grow entirely underwater and are best suited for planted tanks, while emergent plants grow with parts rising above water and may only be submerged seasonally. Emergent plants can thrive in open-topped tanks where leaves access air. Always ensure safety to prevent escapes.

CO2: Enhancing Plant Growth Responsibly

Carbon dioxide is a key component for aquatic plant growth. CO2 can be introduced through several systems:

• Gaseous CO2, using DIY yeast generators, aerosol canisters (value for money but limited control), or pressurised systems offering precise regulation and diffusion methods.
• Liquid CO2 fertilisers that are less efficient but economical for smaller tanks.

CO2 overdose can be fatal for fish. For safety, use timers to stop CO2 injection before lights go off and maintain concentration below 30 ppm.

Substrate Selection and Nutrient Supply

The substrate anchors plants and supplies root-accessible nutrients. Although liquid fertilisers support plant nutrition, roots naturally absorb from soil-like media. Options include:

• Complete commercial substrates containing essential nutrients, varying in grain sizes and colours, ready to use.
• Layered approach: base layers of aquarium-safe compost overlain with gravel or sand to prevent cloudiness, though some disturbance can occur over time.
• Plain gravel or sand with root fertiliser tablets for nutrient spikes; useful for rejuvenating old substrates.

Recommended Aquatic Plants for Your Tank

Nymphaea lotus: Before floating leaves appear, underwater leaves show appealing green, red and brown hues with purple spots. Allowing growth to the surface produces fragrant flowers.

Vallisneria Americana var. asiatica: Tall, twisted green leaves make this a great background plant. It propagates through runners and is easy to maintain.

Hemianthus callitrichorides 'Cuba': Among the smallest aquarium plants, with tiny millimetre-sized leaves, it rapidly carpets the foreground, offering aesthetic beauty though requiring care.

Step-by-Step Guide to Setting Up and Maintaining a Planted Tank

Step 1: Preparing Your Aquarium

Choose an aquarium size appropriate for your space and plants. Install a nutrient-rich substrate suited to your plant choices, rinsing it to reduce cloudiness. Arrange hardscapes such as stones and driftwood to create an aesthetic and functional layout.

Step 2: Plant Selection and Placement

Select aquatic plants suited to your tank environment, considering light requirements and growth habits. Plant taller species like Vallisneria at the back, and smaller carpet plants like Hemianthus in the foreground. Use tweezers for delicate plants to avoid root damage.

Step 3: Lighting and CO2 Management

Install suitable aquarium LED lighting designed for plant growth. Adjust light duration, generally 8-10 hours daily, to mimic natural conditions. If using CO2, choose an appropriate system and regulate realistically to avoid fish stress.

Step 4: Nutrient and Water Quality Maintenance

Monitor water parameters regularly, maintaining stable pH and temperature. Supplement nutrients using liquid fertilisers or root tabs as needed. Conduct regular water changes to keep the environment balanced and reduce algae risk.

Step 5: Ongoing Care and Troubleshooting

• Trim plants regularly to encourage healthy growth and prevent overcrowding.
• Watch for algae growth and adjust light, CO2, or nutrients accordingly.
• Ensure fish and invertebrates are compatible and healthy, helping maintain a balanced ecosystem.

Conclusion

Growing plants underwater in a planted tank is a rewarding hobby that combines science, patience, and creativity. By understanding plant needs for light, CO2, nutrients, and substrate, and by maintaining stable and balanced conditions, you can create a vibrant, healthy aquatic environment that enhances your aquarium’s beauty and benefits its inhabitants.

Start small, research your chosen plants’ specific care requirements, and watch your underwater garden flourish!