University of Vermont Extension 
Department of Plant and Soil Science

Anytime News Article
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WATER GARDENING
 
Dr. Leonard Perry, Extension Professor
University of Vermont
 
 
Small water gardens and ponds can add beauty and tranquility to gardens.  Proper location, installation, choice of plants, and care will ensure your water feature lasts for many years with a minimum of problems.

On a larger scale, you can create a water garden by digging a pond or small pool. For the most variety of plants, you should make it a minimum of about 2 feet deep and 4 to 6 feet across. Once the hole is dug, line it with 2 to 3 inches of sand, with a PVC pool liner on top. Black plastic can be used, but use a thick grade and several layers. The sand keeps the bottom of the liner from contacting rocks and being punctured.

On top of the liner you can place thick black felt pond liner. This felt keeps washed river stone, which you may then wish to add, from puncturing the liner from the top. If you're going to add a pond pump, underwater lighting, fountains, or blocks for your pots, now is the time. Many of these supplies can be found at local home and garden supply stores, larger garden centers, or from mail order sources (look for their ads in garden magazines).

The edge of the pond can be finished with bricks or flat stones such as slate for a more formal effect. Simply lay these around the pond, over the edge of the liners. Native stones placed irregularly will give a more informal edge, just make sure they are stable.

Tub gardens can be created from whiskey barrel halves, lined with plastic or rigid liners made specially for this purpose. Old plastic trash cans, halves of plastic drums, large ceramic pots, metal or plastic cattle troughs are other sources of tub gardens. Attractive barrels may be left on the ground, or the less attractive ones sunk about level with the surface. If sinking, keep the edge a few inches above the ground to keep soil from washing in.

Most the plants will be in pots, sunk in the water. Depending on the plant, you can place them at various heights by means of various heights of blocks or bricks placed underneath them. Or, when digging a pond, create stepped terraces as various levels. Water lilies for instance might be placed a foot below the water's surface. Place oxygenating grasses on the bottom. Place other perennials in pots just below the water's surface.  Make sure and check your state list of invasive water plants so you don’t use them.  These may include flowering rush, watermilfoil, frogbit, parrot feather, purple loosestrife, yellow floating heart, and yellow iris.

Algae is one of the few problems in tub gardens, and is seen as green growth in the water. This often happens in the spring and early summer with higher light and warmer temperatures. Once a balance of enough plants, and perhaps other life is established, it should clear. The other life includes tadpoles or snails. If algae forms blankets, it can be removed with a notched stick of piece of rough wood, poked into the mass, twisted, then drawn to the side and out. A filtration system, as in pools, can help remove free-floating algae.

Soil for water plants consists of two parts ordinary garden soil and one part well-rotted cow manure. If available, use equal parts garden soil and pond muck (the soil from the bottom of a pond). If neither muck nor manure are available, add a half cup of bonemeal per bucket of soil. Avoid more fertility as this will only increase the algae. Once planted, line the top two inches of the pot with sand or washed gravel. This helps prevent algae growth.

Most pots can be used for plant containers, but should be large enough for the plants grown. Special wooden pots (cedar or cypress) or perforated plastic cages or mesh baskets are often used.  I use clay pots that I make sure and remove in winter when I drain my small pond.

Some water plants withstand freezing but most don't. Even the hardy water lilies will survive if in large ponds below the ice, but not if frozen. For most smaller water features in the north, bring the pots of lilies and water plants indoors for the winter.

In late fall remove the containers of plants, cleaning off the old leaves and dead foliage. If you won't be putting back into tubs of water indoors, let pots drain overnight. Then place in plastic bags left open at the top. Move aquatic plant pots to a garage or cellar where they won't freeze, such as at 32 to 35 degrees F. Keep moist, not letting them dry out, over winter.  For me, tropical water plants such as water hyacinth and water lettuce need part light and air temperatures about 55 degrees (F) or above, in a small tub of water, to overwinter successfully.  Place back outdoors in your water feature in spring, once freezes and frosts are past and you have cleaned it.

Large water features, such as ponds, in the north will need to be deep enough to not freeze if hardy water plants and fish are to be left in them over winter.  This may be a minimum three to five feet deep, depending on your climate zone.  Keep in mind that in some cities and towns, ponds deeper than 18 inches may be considered pools and so need to be fenced.  If ponds aren’t deep enough, or start freezing anyway, try either a pond heater or a plastic ball on the pond surface.  As the wind moves the ball around, it will keep the surface from freezing. 

Much more on pond types, accessories, and all aspects of successfully installing a pond can be found in the articles from Garden Supermart (www.gardensupermart.com).
             

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