A visit to any large garden show will illustrate the fact that water features are now considered almost indispensable to modern landscape design. A large, well-maintained pond, covered with blooming water lilies, can provide a striking impact to the garden that few other landscape fixtures can match. Of course, not everyone has the space or the time to maintain a full scale pond, but fortunately there is a viable alternative. Container water gardens, popularly known as 'tub gardens', have provided many people with a simple means to engage in the hobby of water gardening.
     A well-conceived tub garden can vary in concept from a lined oak half-barrel containing a colourful mix of aquatic plants, to the more exotic look of an awe-inspiring Lotus bursting forth from a glazed ceramic pot. One advantage of tub gardens over ponds is the warming effect that the sun has upon an above-ground container of water as compared to a large, deep, pond. It is surprising just how warm the water can become in a tub garden on a sunny spring day, thus enabling gardeners in temperate climates, such as the Pacific Northwest, to grow aquatic species that would normally languish in a cool pond. The subject of water temperature will be mentioned again as the two different themes that can be used in the design of tub gardens are examined.

The 'Mini-Pond' Tub Garden

     The 'pond style' of tub garden is essentially a miniature aquatic eco-system that in its most ambitious form, can even include fish. A lined wooden half-barrel can be used for a container if a 'rustic look' is desired, or a glazed ceramic pot can be chosen for a more formal appearance. If you plan on adding fish to your tub garden, it is advisable to install a small water pump to ensure that there is sufficient oxygen, particularly on warm summer days. Warm water contains less oxygen than cold water and fish can quickly become stressed unless the water is circulated continuously throughout the summer. The movement of the water ensures that carbon dioxide reaches the surface of the water, where it is released into the air and replaced by oxygen. The pump can supply water to a spouting ornament such as a figurine or bamboo spout; many people find the concept of moving water appealing even if they choose not to have fish.
     There are a wide variety of aquatic and semi-aquatic plants that will thrive in a small tub garden, and it is beyond the scope of this article to discuss all of them. It will suffice to say that a well balanced selection would include leafy submerged oxygenators such as Elodea or Hornwort (Ceratophylum demersum), some 'marginal aquatics' represented by plants such as Arrowheads, Irises, and Rushes, to name a few, and lastly, a few of the tropical floating aquatics such as Water Hyacinth and Water Lettuce will also help to clarify the water and prevent algae blooms.
     If a sunny location is available, the tub gardener should consider adding a dwarf hardy water lily to the mini-pond. The diminutive leaves and flowers of dwarf water lilies are perfect for tubs and add a touch of realism to the overall appearance of small water gardens. Although there are hundreds of varieties of hardy water lilies, with flowers in colour shades of red, pink, yellow, white and orange (changeables), only a handful of varieties are small enough for tub gardens. Examples of hardy water lilies suitable for tubs are the red flowering 'Perry's Baby Red', the pink flowering 'Joanne Pring', the yellow flowering 'Helvola', the white flowering 'Walter Pagels' and the orange flowering 'Aurora'.
     When setting up a tub garden, it is customary practice to confine each plant to its own pot rather than filling the bottom of the tub with soil and planting directly into the mud. There are several reasons for using the individual pot method. The optimum water depth for aquatic plants varies depending upon the species and by placing upside-down flower pots or bricks on the bottom of your tub, each plant can be placed shallow or deep, according to its needs.
     The nutrient requirements of aquatics varies as well. For example, it is recommended to feed water lilies with special slow-release fertilizer tablets several times during the growing season in order to promote blooming.. Individual pots allow the water gardener to feed only those plants that require an extra boost of nutrients. The pots will also confine the more rambunctious aquatics and prevent them from crowding out their neighbours in small ponds.
     Potted plants are also an advantage when preparing for winter, particularly if a glazed or terra cotta bowl is being used for the tub garden. In an areas subject to below-freezing temperatures, which includes all of Canada,  the bowl is in danger of cracking if it is left outside full of water over the winter. Ceramic pottery has no flexibility whatsoever, and even a few centimeters of ice may exert enough pressure to shatter a ceramic pot. When winter looms, it is therefore advisable to remove the plants and empty the bowl, which can then be stored upside down or in a dry location. Unglazed terra cotta requires even more protection, as even a hard frost can cause spalling (flaking) of the surface.
     Pond plants also need to be protected from freezing and perhaps the most convenient way to do this for  temperate zone gardeners (Pacific Northwest) is to purchase a large plastic tub, commonly known to gardeners as a 'muck bucket'. In late Fall, hardy aquatic plants are simply transferred into the bucket, which is then filled with water. The plastic is flexible enough to accommodate the formation of ice without cracking and the water insulates the plants against freezing. In climates colder than zone 8, the pond plants will need to be placed in a cool location indoors, unless a large, deep pond is available for winter storage.
     Tropical floating plants, such as Water Hyacinths, are usually considered to be the water gardening equivalent of bedding plants and are composted or similarly disposed of by late fall. Tropical marginal plants such as Taros or Umbrella Plants are quite happy to spend winter indoors on a sunny windowsill in a secondary role as houseplants.

The 'Specimen' Tub Garden

    If the mini-pond is considered to be essentially an outdoor aquarium, the intention when installing a 'specimen tub garden' is to create a landscape feature. The main difference between the two is the manner in which the displays are viewed. The mini-pond style of tub garden is intended to be viewed from above; a typical installation would be on a deck or patio, with a group of lawn chairs surrounding the miniature pond. With the 'specimen' tub garden, the viewer must step back even further. The intention here is to install a bold landscape feature, usually a single plant per tub, and one that is worthy of a prime position on the deck, patio or lawn. This is not a new concept, for tubs of lotus and tropical water lilies have graced the courtyards of Bali, China and Thailand for hundreds of years.
     The warmth conveyed to the water by a tub garden situated in a sunny location allows even a gardener in the cool Pacific Northwest to transfer a prized tropical water lily from the confines of the greenhouse to a favoured summer location outdoors. A small hardy water lily could also be placed in such an environment, but there are several reasons why a tropical can be more rewarding, albeit requiring more effort. Many varieties of tropical water lilies blossom in stunning shades of blue and purple, colours which are impossible to obtain from hardy water lilies. Tropicals are also profuse bloomers, a single plant often producing multiple flowers simultaneously. In addition, the blooms of certain varieties of tropical lilies are intensely fragrant, an important bonus if the tub is placed on the deck or patio. Unlike the hardies, tropical lilies raise their flowers up to 12 inches or more above the water, a pleasing effect even from a distance.
     This characteristic is even more pronounced in the Lotus, known in horticulture as the genus Nelumbo. A mature lotus will often produce blossoms on stems 4-5 feet tall, rising above huge leaves which in turn are elevated 3 feet or more above the water. Unlike the tropical water lilies, lotuses are hardy perennials in many parts of Canada and winter care is similar to that of the hardy water lilies.
     If the landscape design calls for a more subdued statement, the giant Papyrus: Cyperus papyrus, is an elegant specimen for the tub garden. This striking species, although not hardy in Canada, is surprising easy to grow and will readily fill a 3 foot diameter container in a single season.
     If the winter storage of a large, tropical aquatic presents a problem, there are hardy species which are also showy enough to serve in specimen tubs. Even the lowly cattail, inhabitant of marshy ground across Canada and the USA, has a desirable green and white striped form: Typha latifolia 'Variegata', which is perfectly suitable as a specimen plant. If a 'tropical look' is desired, a clump of Hardy Thalia (Thalia dealbata), a winter-hardy marginal aquatic plant resembling the famous Bird of Paradise, will effectively fill the role. 
     At first glance, it may appear to some that water gardening within the confines of a 3 foot diameter container is an uncomfortably restrictive proposition. But, as with other forms of gardening and landscaping, it may well be the limits of our own imaginations which truly binds us.

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