Watercress Pond Plant Growing, Care & Seeds Guide (Nasturtium officinale)

Watercress (yellow cress) belongs to Brassicaceae, the mustard family, which was formerly known as Cruciferae – so named due to members of this family possessing four-merous flowers that resemble a crucifix or cross shape. Native to Europe, India, western Asia, and northern Africa, Nasturtium officinale has since been introduced to North America and Australia, where it is largely considered a noxious weed and, in some areas, is highly invasive and capable of overtaking natural ecosystems.

Watercress is hermaphroditic, with each flower possessing both male and female parts, and is capable pollination via wind and water dispersal of pollen and seeds (respectively), or by means of bees, butterflies, moths, and flies, all of which rely on this plant within Nasturtium’s native range. It’s also able to spread vegetatively by simply falling over, the stems becoming roots that new shoots can then spring from. Its fibrous roots are dined on readily by snails, wild deer, cows, birds, muskrats, shrimp, some fish species, and, of course, humans.

Nasturtium is naturally an exceptionally efficient water and soil purifier, able to adjust its nutrient intake depending upon what’s there. For example, the more phosphorous or nitrogen is present, the more of these watercress’s roots will soak up (there are, of course, limits to this). In a stream in New Zealand that had ammonium, nitrates, and phosphorous present, wild watercress growing in the stream were able to effectively filter these out during the plants’ peak growing times when nutrient uptake is the greatest.

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If planting from seeds, watercress should begin to germinate within a week if temperatures are between 50 and 60° F (10 to 15° C). It grows very quickly, typically reaching full size (up to 20 inches in height, though some wild individuals have been logged at as tall as 75 inches when grown in water) in around 45 to 60 days. Its spread is several meters, so truly one or two watercress plants go a long way.

It does well in either full sun or partial shade, but full shade is likely to kill it. Hardiness zones 3 through 11 work just fine for watercress, though it seems to have the most robust growth in zone 5 and above. Watercress typically begins blooming in late spring, with tiny fruits ripening about 2 months after the first bloom and dropping their seeds not long after that. It’ll continue this cycle usually until the first frost hits, at which point it’ll settle into dormancy for the winter.

Watercress is able to grow in several feet of water with substrate present that it can dig its roots into, marginal water banks, or soil that is kept consistently moist.

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Watercress seeds can be placed in damp soil as deep as 5 centimeters. For already established plants, it can be placed in enough saturated soil to cover the roots and a few centimeters of the stem, or in water that covers has much as half of the stem. If planting in water, either plant it in a pot or aquatic planting basket, or cover the roots with substrate and rocks to deter fish from digging them up and eating them.

Watercress do prefer being planted in water rather than soil, but do well in either. If you wish to harvest watercress to eat, reportedly these plants are less flavorful if grown in soil rather than water.

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Watercress is very resilient, and so long as water or soil is kept within its desired slightly alkaline pH range it should do just fine. If planted in soil, make sure that it never dries out. Nasturtiums grow and spread quickly, so you may want to trim them back as needed to prevent overgrowth. Remove any clippings and fallen leaves and flowers from the pond to maintain healthy water quality. Many ponders utilize watercress in hydroponics systems or bog filters to help filter water that can then flow back into the pond.

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How to Winter Watercress In ponds

Watercress is exceptionally hardy, able to survive in USDA hardiness zones 3 and above. In the autumn, it’ll lose its foliage, leaving only the basal rosette of leaves behind. This will overwinter and should resprout on its own the following spring. If you live in a more temperature region, it may not die back at all and will simply continue its cycle of flowering and fruiting unless temperatures fall below approximately 50° F (10° C). It is not necessary to bring watercress indoors for the winter.

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Outside of its native range, Nasturtium officinale is considered to be quite invasive. It grows quickly and prolifically, thus outcompeting native plants, eliminating native food sources for wildlife, and blocking waterways. In some areas, large establishments of watercress have halted the flow of streams and smaller rivers, allowing water to become stagnant.

If you live in the U.S., 46 states consider watercress to be invasive. Before deciding whether or not you want watercress in your pond, do some digging to figure out whether or not it is legal in your area. Otherwise, you could face substantial fines and also inadvertently cause significant ecological harm if the plant escapes your pond, which is likely considering it can grow either in water or damp soil and wind can carry the pollen and seeds fairly far.

Nasturtium officinale is considered toxic to dogs and cats, but not birds, livestock, horses, people, or most wildlife. There are no known reports of it being toxic to fish.

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Is Watercress Edible? Will Fish Eat it?

Watercress is quite edible, and is loaded with vitamin C (more than is found in oranges!), iron, and calcium due to its ability to readily pull nutrients from soil and water. For centuries, humans have used it in popular dishes, such as vegetable stir fries, as well as medicinally for things such as stomach ulcers and skin inflammation.

Fish, including koi, are likely to dig up and nibble the tasty, fleshy roots so you’ll need to cover these thoroughly with gravel and/or rocks that are too heavy for fish to nudge aside. However, considering watercress spreads easily, it may be a bit of a boon if your fish choose to eat some of it.

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Where to Buy Watercress Plants & Seeds? (UK & US)

Watercress can be purchased readily online, at most pond and aquarium retailers, and at plant nurseries. A quick search revealed that it can even be purchased from local supermarkets in Michigan, where it’s considered invasive. Because of this, please do be diligent in doing your research to make sure that watercress is actually legal to have in your area.

In addition, be very careful to not spread it into natural ecosystems, as it’s very difficult to get rid of once it’s established itself and overtaken native plants.

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