Thermal Mass and The Above Ground Pond

floating pond planter in the above ground pond

Water is a wonderful source of thermal mass in any building. Greenhouses are no exception. Every Growing Dome® Greenhouse Kit comes with an Above Ground Pond that keeps the geodesic Growing Dome warm in the winter and cool in the summer. Each pond is appropriately sized for every Growing Dome. This creates an optimal environment in the greenhouse for year-round growth. Strategically located inside the Growing Dome on the north wall, the pond resides directly under the Reflectix® insulation. The Reflectix aids in keeping the pond warm in the winter and cool in the summer. The pond acts as a thermal battery bank in our greenhouse kits. It is an oval shape in the 15’–26′ Growing Dome sizes and round in the 33’–42′ Growing Domes.

Many Uses of the Above Ground Pond

Greenhouse Pond Painted by Artist depicts an underwater scene of fish swimming, mountains above the water and an eagle soaring

Unique among greenhouse designs, the pond is not just a source of thermal mass. It fosters a beautiful environment for both aquatic plants and fish. The pond also works well as the main fish tank in Aquaponic systems. Plants growing in the raised beds benefit from the humidity provided by the pond. Fish waste is converted into nitrogen with the help of two types of naturally occurring bacteria, so go ahead and give your plants a drink of pond water the next time they are thirsty. The pond needs to be painted a dark color to absorb heat effectively, so it is a great place to get creative.

Thermal Mass Details

First of all, why do we choose water? It is non-toxic, cheap, readily available, allows the gardener to create a pond ecosystem, adds humidity, and its physical composition is perfect for retaining heat. Good thermal mass provides thermal inertia. Its thermal conductivity is high, it is moderately dense, and it has a high specific heat, high heat capacity, and high thermal storage capacity. Water is a better source of thermal mass than brick, stone, or concrete. The Above Ground Pond is appropriately sized for each Growing Dome. As a general rule of thumb, a passive solar greenhouse should contain about 2–4 gallons of water per square foot for optimal solar gain. For example, the 22′ Growing Dome is a 350-square-foot greenhouse and the pond will hold about 900 gallons of water, which equals about 2.6 gallons of water per square foot.

greenhouse pond covered in ivy with a green table and chairs in front
Greenhouse Pond covered in Ivy

**For Dome Owners with in-detail pond questions about pond care & maintenance, fish, pond plants, and recommended products please see our article, How to Create a Beautiful Pond Garden.

Common Floating Plants for the Pond

Floating Plant Islands in the Greenhouse Pond
Floating Plant Islands in the 33 Growing Dome Greenhouse

Duckweed, Azolla, Water Lettuce, Water Hyacinth, Parrot Feather, Water Lily, and Frogbit are the most common floating water plants for the Above Ground Pond in the Growing Dome greenhouse. Floating islands work well for plants that need a substrate or media to grow into, such as gravel. Growing Spaces recommends covering 65–80% of the pond surface with floating water plants, floating plant islands, or shading the surface of the pond to prevent algae blooms. The floating plants listed here do not need a floating island. For more information, see our water garden links and resources document or our aquatic plants article.

Common Fish for the Pond

Floating plants in the pond rely on the fish for their nutrients. The freshwater species of fish listed below are the most common types of fish raised in the Growing Dome pond. Local pet stores or fisheries are the best places to get freshwater fish, but they may also be purchased online and shipped to your door overnight.

  • Goldfish
  • Koi
  • Yellow Perch
  • Freshwater Sunfish, such as Bluegill
  • Catfish
  • Bass
  • Tilapia
Goldfish in the Above Ground Pond

We recommend waiting a few weeks after adding your water plants before introducing fish into your pond. This lets the environment adjust and be more stable for your fish. It is also important to treat tap water and test well water before adding fish to your pond. Water softeners are not recommended for your above-ground pond because they replace electrolytes necessary to your fish (calcium and magnesium) with sodium, resulting in death of the fish.

Solar Powered Waterfall Option

You can also add a Solar Powered Waterfall Option to add to the beauty and elegance of the pond. It also increases the oxygenation of the pond. Or create your own custom feature or add an aerator.