Longwood canna is a beautiful aquatic plant that will thrive along the margins of an ornamental pond. This variety is a hybrid between Canna glauca and Canna x generalis, which are known for their stunning foliage and striking summer blooms. This specific hybrid was first cultivated in Longwood Gardens, a sprawling botanical garden and horticultural research center in Philadelphia.
Both parents of this cultivar belong to the Cannaceae family of canna lilies, of which there are around 10 species. They are not considered true lilies and are more closely related to the Heliconia, Ginger, and Arrowroot families. Native to tropical and subtropical regions of the Americas, canna lilies are now naturalized as far as Asia and Africa.
This herbaceous perennial is often a customer favorite in plant nurseries because of its broad leaves and bright loving flowers. The plant itself can grow to be quite tall, sometimes reaching a height of 6 feet (180 cm) in suitable climates! Its bluish-green leaves are soft to the touch and are shaped like lances.
Its flowers are 3 – 6 inches (7.6 – 15 cm) wide, theatrically rise above the foliage, and are an unforgettable shade of coral pink or peach. When ambient conditions are favorable, the flowering period of Longwood canna can last from mid-summer to fall or until the first frosts occur.
Facts, Benefits & Uses of Longwood Canna
Though Canna glauca tends to grow best under tropical conditions, Longwood canna and several other water canna cultivars are able to tolerate mild temperate climates. If you intend to grow these around your pond, it is advisable to make use of containers that are placed deep enough to fully submerge the canna root systems. Their spreading rhizomes or tubers are quite needy when it comes to nutrients, and may benefit from fertilizers used for other aquatic plants. They can even aid in extracting potentially harmful nutrients and pollutants out of your pond water.
The blooms of Longwood canna will certainly attract numerous pollinators, including hummingbirds, to your pond! If you’d like to create a haven for bees and butterflies in your garden, consider lining an entire wall or allocating a whole pond edge for canna cultivars. As they tend to have extended bloom periods, they can keep your surroundings quite colorful even after the blooms of other plants have long disappeared. Moreover, several parts of this plant are edible and are thus safe around pond inhabitants and house pets.
Longwood Canna Growth, Hardiness & Climate
Canna glauca and its varieties normally thrive in marshes, swamps, and around lakes in the wild. The growth of Longwood canna is often influenced by the condition of its rhizomes prior to planting. Firmer, plumper, and overall larger rhizomes are more likely to produce taller plants and more eye-catching flowers. Rhizomes with more growth points, technically referred to as “eyes”, may allow the plant to obtain more nutrients and become well-established at a quicker pace.
To encourage continuous or repeated blooms throughout Longwood canna’s flowering period (mid-summer to fall), you will have to deadhead the plant. This is done by removing flowers and fruits that are spent. It may a bit more complicated than it sounds as a single spike can produce multiple flowers. The right tools must be used to ensure that the plant doesn’t suffer from damage. Consult the “How to Care for Longwood Canna” section below for more detailed instructions.
How to Plant Longwood Canna
The best way to plant Longwood canna is by using its healthy rhizomes. Make sure to select for those that have many “eyes” or growth points. These should be placed around 4 – 6 inches (10 – 15 cm) deep in rich, loamy soil after the final frosts have passed or when the substrate is at least 18˚C (65˚F). Ideally, the growth points should be facing upward. Once you’ve flattened the soil on the surface, cover it with a thin layer of aquatic gravel or small stones. The set-up should have enough water to submerge the rhizomes under a depth of around 6 inches (15 cm).
If you have a greenhouse or cold frame, you can do this ahead of time. Keep in mind that if you’d like to grow these out of containers or baskets, rhizomes should be spaced far apart. As Longwood canna can eventually have a spread of 2 – 3 feet (61 – 91 cm) wide, each individual is best grown out of its own container. Allow the rhizomes to get acclimatized to their containers prior to transferring them into your pond.
Once the roots are established, you can move your Longwood canna deeper into your pond or until a depth clearance of up to 10 inches is met. Provide your plant with a slow-release fertilizer to ensure that it does not starve for nutrients during the growth period.
How to Care for Longwood Canna
Longwood canna is fairly easy to maintain and will not require much in terms of aftercare. For this reason, it has received the RHS Award of Garden Merit. Do watch out for pests, however, as this hybrid is notorious for attracting quite a few in the warmer months. Keep an eye out for the following pests: caterpillars (especially the canna leaf roller), snails, slugs, and beetles, which can damage canna lily leaves substantially.
As mentioned above, you may have to consistently “deadhead” your canna flowers to ensure that the plant blooms for as long as possible. If you do not deadhead your Longwood canna, it will dedicate its energy stores to producing more viable seeds instead of flowers. With sterilized pruning shears or a sharp pair of scissors, snip off flowers as soon as they begin to fade and pull off any seed pods that are starting to develop. Once the entire flower stalk is spent, take your sterilized shears once more and cut the stalk directly above the node from which it arises.
How to Winter Longwood Canna
Longwood canna can tolerate winter conditions in USDA zones 8 – 11. If you live in these zones, you can leave your canna outdoors all year round. If you live in cooler areas, you may need to bring your plant indoors for the duration of winter. Keep the pot or basket in an area that remains frost-free and make sure that the soil stays evenly and consistently moist. The substrate need not be waterlogged at this time.
Unable to bring plants indoors? You can treat your Longwood canna as an annual and dig out its rhizomes towards the end of autumn or before the first frosts occur. Do this by cutting down the plant, which should mostly be brown once temperatures have dipped to below freezing, to a height of about 6 inches (15 cm). Grab hold of the cut shoot and pull to lift out the rhizomes.
To prepare rhizomes for cold storage, remove any remaining soil and dry them out properly. Store them in a box of compost, vermiculite, or cedar shavings, and make sure the substrate does not grow too dry or too moist throughout winter. Keep the box in a cool area (at most 10˚C or 50˚F). Rhizomes can be replanted outdoors after the final frosts.
Is Longwood Canna Invasive or Toxic?
Longwood canna has the potential to grow aggressively in warm areas as its rhizomes can spread and produce new plants. This particular hybrid is not known for being invasive, however, as it is mostly cultivated in temperate zones with fluctuating temperatures. If you’re concerned about Longwood canna overgrowing your pond or water garden, make sure to restrict its spread to within containers or baskets.
Like all canna lilies, Longwood canna is non-toxic. It’s a safe plant to have around fish and other pets. Do be aware that a flowering plant with a very similar common name, calla lily (Zantedeschia aethipoica), can be highly poisonous to pets.
Where to Buy Longwood Canna & Seeds? (UK & US)
Canna ‘Erebus’ or Longwood canna can be purchased from plant nurseries and online plant portals that carry canna lily hybrids. Pay close attention to the cultivar name when searching for this plant as all of their rhizomes and young shoots can look very similar to one another. If you’re unable to find this specific hybrid in your area, you may opt for other Canna glauca cultivars, such as canna ‘Endeavor’ or canna ‘Panache’.
