Prepare your aquarium to support Hygrophila "Compacta." This plant is generally very tolerant of its living conditions, provided your aquarium has the small amount of surface area it requires. The pH of the water should be between 6.0 and 8.0. The general hardness of the water should be less than 350 parts per million, meaning that Compacta can tolerate fairly hard water.
Obtain some cuttings of Hygrophila "Compacta." Select a side shoot with several nodes, from which roots and leaves will emerge. Cut off a 4-inch length of the shoot with a pair of sharp scissors. Compact cuttings suitable for transplanting are also readily available from aquarium suppliers.
Lay down a substrate of fine gravel in your aquarium if not already present. Your aquarium will typically have a substrate acceptable for Compacta. Bury the cut ends of the shoots in the substrate. Ensure the cuttings are not too close to each other, or they will not get enough light. Anchor the cuttings in place with pieces of bogwood.
Apply liquid fertilizer, according to the instructions. Hygrophila "Compacta" will develop yellow leaves if the water does not have enough nutrients.
Trim Compacta stems with sharp scissors to keep it from outgrowing its space. The existing leaves will typically drop off the cutting when you transplant, but will grow rapidly once it establishes its root system. Hygrophilia "Compacta" will frequently flower when the stems emerge from the water.