Greenhouse pond gardening can be rewarding and crucial to the health of the pond. Why would you want a pond garden in your greenhouse? To help you grow crops year-round! Read all about it in our guide to greenhouse pond gardening and learn which plants are the easiest to grow.
Growing Domes are unique among greenhouses because we use an above-ground pond to provide thermal mass. This helps domes to stay warmer in the winter and cooler in the summer. And that allows year-round gardening in regions where outdoor winter gardening is not possible.
In this post we discuss some of the easiest plants to grow in your greenhouse pond: frogbit, parrot feather, taro (kalo) and water lettuce.
First, a little information about pond plants. We will discuss Zone 4: Deep Water and Oxygenating Plants and Zone 5: Floating Plants.
Zone 4 plants tend to do the most for the health of the pond. They remove excess nutrients and replenish the pond’s oxygen. Water Hawthornes, Water Lilies and Water Violet are examples of Zone 4 plants.
Zone 5 plants are floating plants. They are surface water plants and do not need a plant basket. They provide cover from the sun for your pond as well as providing a resting place for frogs, newts, floating duck decoys and other dome greenhouse friends.
Greenhouse Pond Gardening: Growing Frogbit
- Family: Hydrocharitaceae
- Botanical Name: Limnobium laevigatum
- Common Name: Amazon Frogbit, frogbit, spongeplant
- Type: Perennial, floating water plant
- Optimal Temperatures: 39 – 95 F, 4 – 35 C
- pH: 6.5-7.8
- Water Hardness: Soft – medium hard water
Frogbit is a floating aquatic plant that originated in Central and South America. Its natural habitat is lakes, ponds and slow-flowing rivers. It is an emersed plant and prefers moderate light.
As an emersed plant, frogbit does best if the tops of the leaves remain dry. It is a perennial with smooth, round leaves. Simply place it on the surface of your pond and watch it grow! Be sure the water has enough nutrients to keep it happy.
Frogbit is a wonderful option for your greenhouse pond garden. It is a fast growing plant and will quickly provide cover in your pond, but it can be invasive. It was introduced in California as an ornamental pond plant, but escaped into the Sacramento river delta and the San Joaquin River. NOTE: Do not flush frogbit down the toilet and do not plant it in outdoor ponds. This will help keep open water resources free from invasion.
Frogbit Care
To keep your frogbit happy and healthy, pay attention to the pond temperature and pH. Performing an annual (or as needed) water test will tell you about the nutrients in the water as well as the pH.
Due to frogbit’s rapid growth be sure your water has enough nutrients to feed your plants. If the leaves are yellowing, rotting or melting, it could be that nutrients are lacking in the water.
Frogbit provides cover for your pond, a hiding place for fish if you have them and it absorbs extra nutrients. This helps prevent algae growth as well as helping to maintain water quality. Another benefit is that during photosynthesis, frogbit releases oxygen which helps with the oxygenation of your pond.
Greenhouse Pond Gardening: Growing Parrot’s Feather
- Family: Haloragaceae
- Botanical Name: Myriophyllum aquaticum
- Common Name: Parrot’s feather, parrot feather watermilfoil
- Type: Perennial, floating water plant
- Optimal Temperatures: 39 – 95 F, 4 – 35 C
- pH: 6.8-8.0
- Water Hardness: Soft – medium hard water
Parrot’s feather is native to the Amazon River in South America. Its natural habitat is freshwater streams, ponds, lakes, rivers and canals with high nutrient contents. It is now found on every continent with the exception of Antarctica.
It gets its name from the feather-like leaves and can grow to be a foot above the water. Parrot’s feather plants can produce light pink flowers in the spring and fall. The plants do best when the water begins to warm and their leaves range from a blue-green to gray-green.
Parrot’s feather is a natural water filter, adds oxygen to the water as well as keeping algae in control. On the downside, it is an ideal mosquito breeding plant so we recommend having fish in your pond to eat the mosquito larvae.
Parrot Feather Care
Place parrot’s feather on the surface of the pond or underwater to encourage oxygenation. It will grow fastest with 6-8 hours of sunlight per day. Although it can tolerate morning-only sun, it will not be as effective in improving water quality and will have a slower growth rate. NOTE: Parrot’s feather plants can create a dense mat on the surface of the water. Its woody stems can also grow to 5 feet in length. In warmer climates, it has been known to grow to such extremes as to inhibit fishing and water sports, entangle swimmers and choke out native plants. It is important not to let it escape your pond garden!
As a warm climate plant, it will not survive cold climate winters in an unheated dome greenhouse. It will die back to the rhizomes. If the dome is unheated then the parrot’s feather plant is considered an annual as it will not survive the cold.
Parrot’s feather can have pest issues with spider mites, scale, aphids and mealy bugs. To treat organically, iInsecticidal soap can be used for all of these pests. Other organic options are to introduce ladybugs or other beneficial insects. Neem oil may be used against spider mites and aphids. Use rubbing alcohol to treat scale. We recommend removing the plants from the pond and placing them into another container when applying pest treatments.
Greenhouse Pond Gardening: Growing Taro (Kalo)
- Family: Araceae
- Botanical Name: Colocasia esculenta
- Common Name: Taro, kalo, talo
- Type: Herbaceous, aquatic or dryland plant
- Optimal Temperatures: 77 – 95 F, 25 – 35 C
- pH: 5.5-6.5
- Water Hardness: Slightly soft to moderately hard water
Growing taro can add to the beauty of your pond or your greenhouse beds. Taro is grown around the world, however, in Hawai‘i and a few other areas it is grown either as a wetland plant or dryland plant. Ancient Hawaiians created a very sophisticated gravity-fed system by working with nature. They built lo’i (wetland kalo fields) beside freshwater sources using rocks. This allowed the water to flow in and out, constantly replenishing the corms with nutrients.
Dryland taro needs moist environments and relies on rainfall or constant mulching to retain moisture. It was grown by putting the huli (part of the stem) into a mound of soil, leaving room for the edible corm to grow. It can take dryland taro 8-12 months to mature.
Taro or kalo is considered one of the most ancient cultivated crops. Taro was a “canoe plant” and was brought across the Pacific Ocean by Polynesian voyagers somewhere around 1300 BC. Hawai‘i is one of the few areas where wetland cultivation developed. The edible tuber of kalo became a favored staple food and is revered in Hawaiian culture.
Taro in Culture
In Hawai’i the mo’olelo (story) is that Hāloa was a stillborn child buried in the soil and watered by the tears of his mother until a green sprout appeared. A heart-shaped leaf grew and the first kalo (taro) plant took shape. When Ho‘ohōkūkalani gave birth to a second son she named him Hāloa in honor of his brother. Hāloa means everlasting breath and according to the legend he was the first human.
Hāloa continued to care for the kalo plant as his older brother throughout his life and in turn, the kalo plant nourished the ‘ohaha (family) of Hāloa. Native Hawaiians have a deeply rooted kuleana (responsibility) to care for and honor the kalo plant just as they would care for a sibling. And don’t most gardeners care deeply about their plants?
Can you tell that kalo is my favorite? That’s because I lived in Hawai‘i. Kalo is a beautiful plant with heart-shaped leaves and some varieties are edible. Did you know that the Hawaiian language was originally strictly an oral language? Due to that there are many layers to sayings, not just double meanings.
Here’s a fun saying about kalo: ‘Ai no i kalo mo ‘a. Translation: One can eat cooked taro. In other words: The work is done; one can sit at ease and enjoy himself. Saying #82 from the book ‘Ōlelo No‘eau Hawaiian Proverbs and Poetical Sayings. If you love Hawaiian plants, here’s another amazing book by Marie McDonald Nā Lei Makamae. Marie McDonald was recognized as a “Master of Traditional Art” by the National Endowment for the Arts.
Taro Care
Growing taro as a pond plant is best in a floating basket with an aquatic planting medium or a specialized aquatic soil blend. As an outside pond plant, it grows best in shallow water or in the lo‘i, the wetland irrigation system of Hawai‘i. In any type of soil, taro needs to be consistently wet so a pond is the best option.
If you grow taro in your unheated dome it will not survive the winter in a cold climate. Take it inside your house for the winter months and it will continue to grow if it is near a sunny window. Move it back out to your pond once the temperatures are back up in the high 70s F. Some varieties can grow to be 48” tall and are very striking.
Taro can be attractive to whiteflies. If an infestation occurs, take the plant outside, cut the stem off and dispose of it. It will regenerate and grow a new plant!
Consider planting some taro companion plants in the beds closest to the pond. Lemongrass, marigolds and ginger can help to repel pests.
Harvesting Taro
To harvest the edible tuber, first you must be patient. Taro takes between 7-12 months to harvest and the temperatures must be at least above 25 degrees F.
So what does taro root look like and how do you harvest it? The outer appearance of the root or tuber is similar to a hairy potato! Remember that not all taro are edible. Even the edible varieties need to be cooked as they contain the chemical calcium oxalate. Note: The chemical calcium oxalate irritates the mouth and stomach so do not eat taro raw. If concerned about calcium oxalate wear gloves while handling taro.
Greenhouse Pond Gardening: Growing Water Lettuce
- Family: Araceae
- Botanical Name: Pistia stratiotes
- Common Name: Water lettuce, water cabbage, Nile cabbage
- Type: Perennial in USDA zones 9-11, annual outside its hardiness zones
- Optimal Temperatures: 72- 86F
- pH: 6.0-7.5
- Water Hardness: Soft to moderately hard water
One of our favorite floating plants is water lettuce. The exact origin of water lettuce is a mystery although it is depicted in Egyptian hieroglyphics. There is also evidence of its early existence in South America. Despite its name it is not edible except as a famine food. Note: It is known to absorb heavy metals from open water sources.
It is a perennial plant in warm climates. Water lettuce needs a water temperature that is at least 70 degrees. It will not survive in colder temperatures. It also needs around 11 hours of sunlight, but some shade from the hot afternoon sun will help prevent the leaves from burning. Note: Water lettuce that is grown at a nursery may have been grown in low light. Plan to acclimatize your plant to your lighting levels. Too much light may cause the leaves to turn yellow. Too little light may cause the leaves to be darker than normal.
Water Lettuce Care
Water lettuce needs neutral to slightly alkaline water. Salty water or water with a noticeable lime content can be detrimental. Test your water to determine what the levels are and adjust accordingly. Water lettuce cannot tolerate lime and will only handle up to 2.5 ppt of salt. Another key factor is to aim for a water pH that is between 6.5 – 7.5 and neutral to slightly alkaline or slightly acidic.
And what about humidity? We’re glad you asked! Some of you live in climates with less natural humidity and will need to pay a bit more attention to your water lettuce as it does best in medium to high humidity. Low humidity will cause the leaves to dry out.
Planting and Fertilizing
As a free-floating plant, water lettuce does not need to be planted in a floating basket. The roots will free-float in the water. However, pay attention to the mineral content in your water!
Floating plants get their nutrients from the water and that means you need to check the nutrient levels of the water. If the leaves are starting to turn yellow, that may be due to a lack of nutrients. To help you decide how to fertilize your plants, think about what else is in your pond.
Fertilizer will affect all the living things in your pond. Do you have fish or other plants? If so, consider removing the water lettuce and placing them in a tub of liquid fertilizer for a few hours. To add a liquid fertilizer to the pond, check to see if it is safe for your fish and other plants before doing so. Fertilize the plants separately if you are uncertain about the safety factor for your fish.
We hope you enjoyed this article about growing pond plants. Happy gardening!
