Giant arrowhead, also known as California arrowhead and Aztec arrowhead, is a unique flowering plant in the water plantain family (Alismataceae). Like most other members of this family, giant arrowhead is an aquatic plant, often growing in ponds and marshes. It can frequently be found at the edges of ponds and does well in shallow water.
You may recognize the genus name sagittaria as coming from the Latin word “sagitta,” meaning arrow. As its name suggests, giant arrowhead produces large, arrowhead-shaped leaves. White flowers with burgundy spots and yellow centers appear in the summer and bloom all season long.
Members of the water plantain family are considered to have a cosmopolitan distribution, meaning that they can be found in most regions of the world. The sagittaria genus contains around 30 species of plants, which can be found on several continents. Giant arrowhead, specifically, is native to South America and subtropical areas of the southern United States, with a wide distribution across North and South America. Although its distribution is broad, it is also disjointed, occurring in isolated patches across its range as native habitats have become more and more fragmented and altered by humans.
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Fast growing, a mature giant arrowhead’s lush leaves can grow up to 28 centimeters long and 23 centimeters wide, providing shade for pond margins. Its petioles, or leaf stalks, can grow to 0.75 meters (2.5 feet) long, while the entire plant can grow as tall as 6 feet total in height. Giant arrowhead is easy to care for when planted in the proper conditions, but is not winter-hardy. This plant easily spreads through both seeds and rhizomes, so this is something to keep in mind when selecting it for your pond as you will likely need to cut or separate plants.
In the wild, giant arrowhead can often be found growing in shallow, ephemeral waters. In your garden, giant arrowhead will happily grow at the edge of a pond. To plant giant arrowhead from seed, plant in moist, rich soil in the spring. Seeds need light to germinate. Once the seeds have sprouted, be sure to keep seedlings submerged under water. Leaves will start out thin and underwater, but will expand to their full arrowhead shape once more mature and out of the water.
To plant an established giant arrowhead, place in a large pot and submerge it in your pond so that the plant is covered by 6 inches or more of water. Keep in mind that it will likely grow quite tall, so plant it where it won't block out other plants or things that you'd like to be able to see.
Giant arrowhead is an easy, self-sustaining plant for the most part, as long as it has enough moisture and nutrients. Planting it in the shallow margins of your pond will ensure it has a suitable environment to grow in, especially if you have fish adding to the nutrient contents of your water.
As giant arrowhead spreads through rhizomes, it is worth considering planting it in pots and lowering these into the pond, instead of planting directly into the soil.
Giant arrowhead can survive winters in hardiness zones 7-11 without requiring much extra care from gardeners. In colder zones, dropped seeds may be able to survive the winter but the plant itself is likely to die. If you live outside of zones 7-11, keep in mind that giant arrowhead will most likely not behave as a perennial. If you are set on having this species in your pond, you can either purchase a new plant each year or collect seeds for sowing after the last frost.
As mentioned above, giant arrowhead is primarily found in portions of North and South America. That means that if you live elsewhere, giant arrowhead is technically invasive. This species grows easily, and spreads by both seeds and rhizomes, so it can take hold of new ecosystems fairly easily if you are not careful. Be sure to only purchase and plant it within its native regions!
In Australia, giant arrowhead is considered an invasive weed, as it is becoming an increasing problem there. When not native, giant arrowhead can cause problems due to shading water and out-competing native plants. If you live in Australia, please do not plant giant arrowhead! Even if you live elsewhere, it is a good idea to only plant in your personal pond or water garden (not in natural areas) and plant in pots so that it is less likely to spread.
Giant arrowhead is not known to be toxic to humans, domesticated animals, or wildlife, and is in fact eaten by some wildlife. Ducks in particular enjoy munching on its tender tubers and roots.
Giant arrowhead is edible. In fact, many species in the sagittaria genus are harvested for their edible roots. Your fish are unlikely to eat it, but if they do, they should not be harmed. This is a common pond species and is safe for fish to be around. Be sure to clean any dropped or trimmed foliage out of your pond to limit decomposition in your water and maintain healthy water quality.
In North and South America, giant arrowhead can be purchased from plant nurseries, both online and in person. Elsewhere, online nurseries may be your only option. Since the water plantain family is so widespread, it is worth considering a species that is native to your area. As always, be careful when planting non-native species in your pond—as mentioned earlier, giant arrowhead should not be planted in Australia in particular.
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