Most water plants are easily propagated by plant division or by cuttings. The key to successful water-plant propagation is ensuring an appropriate aquatic environment for the new divisions or cuttings to become established. This includes having fresh growing medium and water that is clean, constantly recirculating, well-aerated and chlorine-free. In a home water garden, these conditions are easily achieved by preparing a small propagation area.
Prepare Propagation Location
Create a space in your present water garden for aquatic plant propagation. Using a flat-bladed shovel, dig a trench 8 inches deep by 12 inches wide to the side of your existing watercourse between your waterfall or inlet and your pond. Level off the bottom to suit your propagation needs. An area 12 inches wide by 24 inches long is sufficient for a single tray of aquatic plants.
Line the trench with rubber pond liner material leaving sufficient overlap with your existing watercourse liner.
Allow the recirculating water from your pond to flow through the trench. Adjust water flow if necessary so that water does not spill over the sides of the trench.
Propagating the Plants
Poke holes in the bottom 1-inch of 4-inch pots using a utility knife or screwdriver. Set 4-inch pots into potting trays, and fill the pots 2/3 full with clay soil or aquatic potting medium. Cut aquatic fertilizer tablets into quarters with a utility knife or sharp scissors, and insert a 1/4 tablet into the clay or potting medium in each pot.
Use sharp scissors to cut 4-inch lengths of vertical stem from each aquatic plant desired for propagation. Alternatively, for plants with thick rhizome systems, gently lift the connected mat of plants and cut a section of rhizome including a vertical stem shoot using sharp scissors.
Place one 4-inch stem section or one rhizome-and-shoot section in each prepared 4-inch pot. Fill the pot to within 1/2 inch of the surface with additional clay soil or potting medium.
Place the tray of filled 4-inch pots into the prepared aquatic plant propagation area. Adjust water flow rate if necessary to ensure that water circulates freely past the tray of pots but does not overflow the water course.
Monitor the plants for growth. When two new leaves have appeared, transplant the propagated water plants to their permanent location.