Tropical water plants either originally came from or were developed from subtropical to tropical regions. Australia is a huge country with climates that vary from cold temperate areas with heavy frosts through to tropical regions. Many tropical aquatic plants can grow well in the subtropics, but become decreasingly tolerant as conditions approach the cold temperate areas. However some species are resilient enough to be able to tolerate frost.
Just as some tropical water plants do not perform well in the cooler regions, the same can be said in reverse with some of the cold tolerant varieties not performing well in the tropical regions. A prime example of this is the Japanese Iris (Iris ensata), which needs a cold dormancy period to rest and then flower well the following Spring-Summer.
The secret to growing tropical water plants in southern Australia.
Tropical water lilies are amongst the most highly desired tropical aquatic plants for ponds in warmer climates, preferring water temperatures above 24°C. These magnificent plants produce flowers that stand up to 30cm high, out of the pond water. Some of the flower colours range from pinks to reds, whites and yellows, but also some of the richest purples and blues.
In cooler climates, tropical water plants should only be planted when the water temperature is above 24°C. Planting too early can cause the plants to go into shock and send them back into dormancy. Most need 8 hours of direct sunlight in order to grow or flower well. If planting in shadier locations, select areas with morning shade so that the plants are able to be in the warmer afternoon sun. Generally larger ponds are slower to warm up, but they are also slower to cool down. This increases the stability in the pond temperature and improves the potential for tropical aquatic plants to do well.
Can I grow Lotus in Victoria and Tasmania?
Yes you can. The trick with these tropical water plants is similar to that mentioned above. Lotus should only be planted or re-potted once water temperature gets above 22°C. This is best done in November-December. Timing is important as the Lotus needs to grow over the Summer months, so that it is strong enough to survive the long cold Winter. Many varieties can be grown successfully this way. Flowering should commence fairly quickly at this time, however it is best to place the plants in a warm position. Sudden changes in weather conditions, particularly cold nights can halt or slow down flowering.
What if I want to grow varieties of tropical aquatic plants that are not cold tolerant?
Some will survive the cold under the water, as they go dormant during the Winter. Oz Watergardens is located in the Yarra Valley in Victoria and we do receive regular frost down to -3°C. There are a number of tropical water plants that grow successfully in our climate, that we feel we can confidently recommend for the cooler climates.
Tropical water plants such as the tropical water lilies can also be removed from the pond, stored indoors in a cool dark place until the leaves dry. When dried the tuberous bulb can be washed from the soil and be stored in a container of damp (not wet) sand. Then store the container in a cool dark place. Re-plant the water lily in Spring when the pond water temperature reaches 24°C.
There is also the option of growing some tropical aquatic plants, replacing them as you would for other garden annuals. Some of the most striking foliage, enticing flowers and beautiful perfumes can then still be grown and enjoyed for most of the year.
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