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Spring has arrived in the water gardens at Denver Botanic Gardens. Hardy waterlilies are breaking dormancy, developing submerged leaves and their first few floating leaves of the season. Aquatic iris, cattails, pickerel plant and lizard’s tail are also showing a flush of new spring growth.
Beyond these changes which can be seen when visiting the Gardens, there are many behind-the-scenes preparations taking place. From propagating plants from seeds, tubers, cuttings and divisions to creating planting designs for each water garden, the horticulture staff and volunteers are busy laying the groundwork for the upcoming summer months.
The giant water platters (Victoria ‘Longwood Hybrid’) that will grace the pools this summer got their start as seeds in our greenhouse in late March. These were provided to us by Longwood Gardens in Kennett Square, PA, where this hybrid was originally developed by Patrick Nutt in 1960.
The pea-sized seeds were placed in a heated tub of water in our aquatics greenhouse with the temperature maintained at 86-88 degrees F. The average germination time is 7-10 days. Once the seeds develop their first leaves and roots, we plant them in 2” containers of sand with a tablespoon of peat moss in the bottom to bring the pH down a bit. The heat can then be turned down to 75 degrees. As the plants grow, they are repotted into larger containers, with a final container size of 8-10” diameter.
In early June, the heat will be turned off in the greenhouse tubs to allow the platters to adjust to the cooler water temperatures they will grow in outdoors. They will then be transplanted into 20-24” solid tubs filled with clay loam and placed in the Monet and Science Pyramid ponds in late June.
The platters are heavy feeders and require weekly fertilization throughout the season. Be sure to visit often to observe their rapid growth during the summer months. You may also find baby ducklings taking an afternoon nap on the strong and buoyant leaves.
Gorgon plants (Euryale ferox) are also grown from seed in the greenhouse during this time. These seeds will germinate in cooler water than the Victoria waterlilies, and have even been known to pop up in our outdoor ponds from seeds that overwintered in the muck at the bottom. Those grown from seed in the greenhouse will be planted outside in May.
Many of the tropical waterlilies you will see during the summer in the water gardens are started from tubers that were harvested from lilies the previous fall. These are stored in our tuber fridge at 55 degrees and are then pulled out in April and placed in tubs of water heated to 75 degrees in the greenhouse. They will be placed outside in late June along with the Victorias.
Umbrella palm and dwarf papyrus, two tropical marginal aquatic plants used in our display ponds, are easy to propagate by taking leaf cuttings. These cuttings are taken in mid-March from larger “mother” plants that are stored in the greenhouse for the winter months. The cuttings are placed in 4” containers of clay loam which are then placed in a tray of water on top of a heat mat maintained at 85 degrees. The bottom heat provided by the mats is necessary to get the cuttings to root in quickly. Within 7-10 days, the viviparous leaves will put up new growth. These small plants will then be sold in the aquatics division of our Spring Plant Sale over Mother’s Day weekend.
Another spring chore that provides us with additional plants for both our Spring Plant Sale and our water garden displays is dividing. On Sundays during the spring, Colorado Water Garden Society members gather for morning work sessions at the Gardens to help divide and repot hardy waterlilies outside along with tropical marginal plants including cannas, taro and papyrus in the greenhouse.
The designs for each water garden are created in January and February. An effort is made each year to add new plant varieties to the collection, and these are ordered from wholesale nurseries in early March. New plants are ordered for the spring plant sale and all are potted on Sunday work days with the Colorado Water Garden Society members’ help. Interpretive signage is also created during this time of year to help educate visitors about any new additions to the aquatic plant collection.
We hope you will join us throughout the spring, summer and fall to enjoy the water gardens at Denver Botanic Gardens. Stay tuned for another blog post this summer with more details about the work that goes into maintaining aquatic plants during the height of the season.