Nymphaea Pennsylvania - Water lily

Tropical water lilies love warmth and cannot tolerate our winters, so they must be protected from the cold. Each rhizome of the 'Pennsylvania' water lily should be planted in a container of 14 to 20 litres, under 20 to 60 cm of water (maximum 80 cm). Choose a lightweight and easy-to-move model (for example, a plastic pot with drainage holes). When the water temperature reaches around 20 °C, the container will be moved outside and submerged in a pond, a tub, a barrel... Plant the rhizomes in loamy soil, rich in clay, sticky, and free of stones (never use potting soil, as it is too light and promotes algae growth). The use of open baskets is strongly discouraged. Fill your container up to 5-8 cm from the edge. Plant your rhizomes vertically, burying them in the soil up to the collar. Place 2 to 3 Osmocote cones (NPK formula: 10-11-18+2MgO+TE) around the rhizome, burying them 5 or 10 cm into the soil. Place a layer of pumice 2-3 cm thick to secure everything. Water the whole thing with the watering can to saturate the substrate. Place the container at the correct depth in the pond or tub. Provide these tropical water lilies with a very sunny location where they will receive a minimum of 6 to 7 hours of full sun daily. Each rhizome should have about 1 m² of water surface to develop properly. Apply fertiliser two to three times between April and August.

To help the vegetation start, place the containers against a south-facing wall around April (depending on the region). Then, position them in their final location (for the season) as soon as frost is no longer a concern and temperatures reach 20 °C. Make sure the water level remains fairly stable and that the water is neither too acidic nor too alkaline (a desirable pH between 6.5 and 7.5).

Wintering: Tropical water lilies must be overwintered if not grown year-round indoors in a heated room. Outside, leave them in place until real frosts are announced. The natural decrease in water temperature is favourable for the formation of bulblets around the mother rhizome and for the plants to enter dormancy. Overwinter your tropical water lilies in their container, which you will place in a 100 to 200-litre container, ensuring the water temperature is maintained between 12 and 15 °C. Place everything in a bright room, such as a cold greenhouse or conservatory. In March, the rhizomes start to grow. This is the time to divide and replant them for placement at the end of April or early May.

You can also remove the rhizome and bulblets from the water at the end of November, rinse them thoroughly, and store them in sphagnum or blonde peat enclosed in a "zip" bag. Place everything in a room maintained at 20°C out of the water. Replant your rhizomes and bulblets in spring when the water temperature reaches 20°C again. Start the culture in a small volume of water that heats up well during the day, for example, in a small basin exposed against a south-facing wall. Place them in their final location as soon as growth is well underway.

Never leave Nymphaea's rhizomes exposed to the sun or air to prevent them from drying out; plant them as soon as you receive or purchase them.

If you have fish in your pond, it is preferable to spread a thick layer of large gravel on the surface of the planted pot to discourage them from digging in the soil, nibbling on the rhizomes, and thus soiling the water. During the summer, remove excessive leaves that grow in the centre of the clump and keep only the most vigorous ones. Also, remove any yellowed or stained leaves and emergent aquatic "weeds" from the surface.