Diving into water gardening

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Are you looking for a way to dip your toes into the world of water gardening before jumping in head first?

A container water garden is the perfect solution. These miniature ponds can provide all of the components of a large-scale water feature – aquatic plants, moving water, fish and the ability to draw wildlife – on a smaller and less laborious scale.

Containers designed to hold water – often referred to as water bowls – are glazed inside and out, have no drainage holes and come in a variety of colors, shapes and sizes. Plastic liners can be added to other vessels such as half whiskey barrels to hold water. When choosing a container, consider the size of the space it will be placed in, the type of plants you want to grow, whether fish will be added, and if a fountain will be used. If you plan to add fish, make sure the container does not contain copper as this is toxic to fish.

Aquatic plants can be divided into four groups based on growth habits: floating, submerged, floating-leaved and marginal. Floating plants such as Water Lettuce (Pistia stratioides) and Fairy Moss (Azolla carolineana) have leaves that float on the water’s surface and roots that trail in the water beneath them. They are excellent for filtering and shading the water.

Eel Grass (Vallisneria americana) and Dwarf Sagittaria (Sagittaria subulata) are examples of submerged plants that grow with their roots and leaves completely beneath the surface. These plants oxygenate the water and feed on excess nutrients, which in turn reduces algae growth.

Floating-leaved aquatic plants include waterlilies (Nymphaea spp.) and Water Hawthorne (Aponogeton distachyos). Growing with their roots anchored in the soil underwater and their leaves floating on the surface, they also shade the water and provide protection for fish from predators.

Marginal aquatics grow in shallow water or boggy soil at the pond’s edge and include hardy species such as Water Iris (Iris virginica, Iris versicolor, Iris louisiana), and Pickerel Plant (Pontederia cordata), as well as tropical species such as Taro (Colocasia hybrids) and Umbrella Palm (Cyperus alternifolius). These plants feed on nutrients in the water and provide habitat for frogs and insects like dragonflies to lay their eggs.

Two primary methods are used to plant water bowls. The first is to add a heavy clay loam to the container. Soil mixes with light materials like peat and perlite should be avoided as these will float to the surface. Plant a marginal or floating-leaved plant directly into the soil and fill the container with water.

A second method is to fill the container with water and place individually potted marginal, submerged and floating-leaved plants inside, leaving space for fish as well as floating plants. A small fountain can be added if the container is placed near an electrical outlet where a submersible pump can be used. If fish are added, opt for small varieties such as goldfish or minnows and avoid large species including koi, which will quickly outgrow a container. A good rule of thumb is to add one inch of fish per gallon of water.

Water bowls are fairly easy to maintain.

Regular tasks include fertilizing marginal and floating-leaved plants monthly during the growing season with an aquatic plant fertilizer (submerged and floating plants feed on nutrients in the water), removing spent leaves and blooms and monitoring for mosquito larvae. Products such as mosquito bits, which contain beneficial bacteria that feed on these larvae, can be added monthly. If algae growth is a problem, algaecides that are safe for fish and plants can be added weekly to maintain water clarity.

Winter care includes draining the container to prevent expanding ice from causing it to crack. Hardy plants can be brought into a garage where they will not freeze solid and should also be kept from drying out. Tropical marginal plants can be moved inside to a sunny room or simply treated as annuals and purchased again the following year. It is important to note that aquatic plants and non-native fish should never be added to natural waterways. Goldfish can be kept in an aquarium indoors through the winter months.

Tamara Kilbane is the curator of Aquatic Collections with the Denver Botanic Gardens. She can be reached at horticulture@denverbotanicgardens.org.

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