Water Hawthorn Facts, Care, Benefits, & Hardiness (Aponogeton distachyos)
Water hawthorn (Aponogeton distachyos)—also known as Cape hawthorn, Cape pond weed, or Cape asparagus—is a floating aquatic plant in the Aponogetonaceae family native to the Cape Provinces of South Africa. It has since become naturalized in California, parts of Western Europe, Southeast Australia, and New Zealand.
Water hawthorn can be identified by its slender, oval-shaped leaves (3 to 6 in. / 7.6 to 15 cm long) and forked, white inflorescence that float on the water’s surface. It also has submerged, linear leaves that lead to a tuberous root buried in the substrate.
The various names of water hawthorn provide information about the plant’s appearance and life history. The specific epithet distachyos is Latin for “two-spiked,” referring to the plant’s pair of flower spikes that meet to form a curling V-shape. As suggested by the genus Aponogeton, which may mean “neighboring water” in Celtic or “without earth” in Greek, water hawthorn can be found on the margins of water bodies or in shallow ponds. Other accounts claim that the genus Aponogeton refers to the Apono people of Western Africa or the Italian healing springs at Aquae Aponi.
Benefits & Uses of Water Hawthorn (Cape Pondweed)
The flowers are reportedly vanilla-scented— similar to hawthorn (Crataegus spp.), from which water hawthorn received its common name. It is often visited by bees, dragonflies, and other pollinators.
In its native South Africa, water hawthorn is used in traditional dishes and medicines. The names for this unique plant in Afrikaans include waterblommetjie (“water flower”), wateruintjie (“water onion”), and vleikos—referring to the seasonally dry vleis (ponds) in which the plant grows. The flowers of water hawthorn are used to make the traditional dish waterblommetjiebredie, meaning “water flower stew.” Waterblommetjiebredie is similar to green bean stew and is usually prepared with lamb or mutton, onions, and a good bit of sorrel. Waterblommetjie’s juicy stem bears a similarity to asparagus, and it can be used medicinally to treat rashes, burns, and other abrasions. The leaves can also be used as a poultice.
Water Hawthorn Growth, Hardiness & Climate
Water hawthorn can be a prolific grower, reaching a height of up to 4 feet (1.2 m) and spreading up to 3 feet (90 cm) across. This plant grows best in temperate and subtropical climates. It falls within USDA hardiness zones 6 to 10, which means water hawthorn can withstand minimum winter temperatures of -10° to -5° F (-23.3° to -20.6° C). Water hawthorn prefers cool, still waters below 70° F (21° C). It will bloom in early winter and spring, becoming most productive in December, which is rare for most aquatic flowering plants. It will often become dormant when it gets too hot in the summer. Water hawthorn prefers full sun though it will grow in partial shade, and it appears to tolerate most pH values.
How to Plant Water Hawthorn:
Water hawthorn grows on the margins of ponds and prefers a water depth of 6 to 24 in (15 to 61 cm). It is best to plant water hawthorn in an area with full sun exposure. Water hawthorn may be grown from seed or from tuber, and you can also plant mature water hawthorn directly into the pond substrate.
If you are growing water hawthorn from seed, be sure to keep the seeds wet from when they are harvested until they are planted. To propagate water hawthorn, start by sewing ripe seeds in a pot that is immersed in at least 3 in (7.6 cm) of water. In one to two months, after germination, move the seedlings to individual pots in a greenhouse, ensuring they remain in water for the duration of their growing period. Plant mature water hawthorn in late spring or early summer after the last frosts have cleared.
You can also grow water hawthorn from its tuberous rhizome. You can either purchase the tuber or divide the rootstock of an existing mature water hawthorn between winter and early spring. Plant the tuber in a pot filled with loam. Place the plant in shallow water and then, as it grows, gradually move the pot to deeper water.
How to Care for Water Hawthorn:
Water hawthorn is quite easy to maintain. Once you have planted the Water hawthorn in a sunny area on the margins of your pond, very little maintenance is required. To increase the rate of growth, you may fertilize water hawthorn while it is actively growing on a monthly basis. Cease fertilization when it is time for the plant to go dormant.
How to Winter Water Hawthorn
Water hawthorn can overwinter outdoors if the pond does not ice over. In fact, in warmer climates, water hawthorn will continue to seed throughout the winter. If your pond is expected to freeze, place water wawthorn in a tub and move it to a greenhouse or a warm area of your home before the first frost. You can place an aquarium heater in the tub so that the water hawthorn stays warm throughout the winter.
Is Water Hawthorn Toxic, Poisonous or Invasive?
No part of water hawthorn is toxic, but its status as an invasive is uncertain. While water hawthorn is not generally considered invasive in the US, it is controlled by Ireland as an invasive plant and is considered an environmental weed in some parts of Australia. There are anecdotal reports of water hawthorn taking over ponds in Ireland, but these examples are scattered and are not sufficient to consider this plant a detriment to your pond.
For now, you should not be concerned when planting water hawthorn. However, if you want to err on the side of caution, you can collect ripe seeds before they have the chance to fall into the water and germinate, limiting the spread of water hawthorn in your pond.
Is Water Hawthorn Edible? Will Fish Eat it?
While it is unlikely that fish will consume any part of the water hawthorn, this plant will improve the habitat complexity of your pond. The floating leaves and flowers will provide shade for fish. Additionally, the submerged leaves and stems will provide a great place for fish to take shelter and lay their eggs. One great benefit of water hawthorn is that it blooms in winter and spring; therefore, it will provide shade and shelter when other floating aquatic plants, like lilies (Nymphaeaceae), have become dormant.