Aquatic animals and underwater vegetation benefit from the shade and temperature buffer provided by shade in a garden pond. Shade also prevents algal blooms that deprive ponds of oxygen. Some aquatic and marginal plants provide shade during the hot summer months and through the fall. In the spring, this vegetation may not have grown in completely from winter dieback, and there is a danger of algae blooms and heat or light extremes.
Install aquatic plants that provide surface cover such as water lilies. Plant these in water between 8 and 18 inches deep, depending on the variety. Free-floating plants such as duckweed, water lettuce and water hyacinth may be added to help you achieve approximately 40 to 60 per cent shade for your pond, which is ideal. Avoid covering more than 65 per cent of the surface of your pond with plants.
Plant marginals such as rushes, dwarf bamboo, cattails and iris at the edges of your pond. Taller marginals are best placed at the southwest edge of smaller ponds to take advantage of the shade provided by the plant’s vertical height. For larger, non-lined ponds, consider planting trees on the southwest side. Some trees that do well in the boggy soils next to large ponds are willows, birches, bald cypress and Eastern red cedar.
Create floating islands of aquatic plants. Determine the diameter of floating island you wish to build. Choose plants for the edges of the floating island that cascade or arch to hide the edges of the floating island. Cut a section of the plastic fencing at least three and a half to four feet wide, and long enough to accommodate the circumference of your floating island. Roll the plastic to form a long cylinder with two inches of overlap. Zip-tie it along the entire length. Zip-tie one end closed.
Stuff the cylinder with the empty, tightly capped plastic bottles until full. Pack them snugly, but make sure you can still form a circle with the cylinder. Zip-tie the ends together to form the closed circle edge of your floating pond. Measure the finished inside diameter of the circle. Cut a circle with these measurements from the roll of plastic fencing. Zip-tie the edges of it to the centre of your floating island.
Mix enough cement mix and water to make a gallon, and fill the empty milk jug with it. Allow it to set for 24 hours. This is the anchor. Tie one end of the rope securely to the handle of the plastic jug. Set your floating island into the edge of the pond. Rinse the roots of the plants for the floating island. Work the roots down into the fencing so that they dangle freely in the water below. Zip-tie the roots gently to the bottom fencing.
Use arbor tape to loosely tie some of the vegetation from the plants on the outer edges so that they cascade over the cylinder edge of the floating island. Tie the other end of the rope to the bottom of the floating island. Gently place the gallon jug anchor in your desired location at the bottom of the pond. The floating island will stay anchored roughly above it.
Plant the floating island densely enough to cover the island, but do not pack the plants in. Allow space for them to fill in over time.
Don’t shade out aquatic plants that need full sun to flourish. If necessary, replant them where they will receive at least six hours of direct sunlight during the growing season.