Consider native flora and ferns are unlikely to spring to mind. That is unfortunate. There are several indigenous ferns, but only a handful are grown or commercially accessible. Hapuu ferns are an exception to this rule. The kupukupu fern is another notable exception.
The kupukupu fern is regaining lost territory throughout new and refurbished environments. Who would have guessed that a McDonald’s parking lot would be adorned with natural plants? Kupukupu does, at a McDonald’s in Oahu’s Temple Valley. Kupukupu is an excellent natural groundcover for industrial and residential environments.
What is Kupukupu Fern?
Kupukupu is an indigenous fern (found in Hawaii and other regions of the world) that is scientifically known as Nephrolepis cordifolia. The name “Cordifolia” translates as “heart-leaved,” which seems a little strange given that the leaves are not truly heart-shaped. The leaves, or fronds, are entirely sword-shaped. Indeed, this fern is also known as sword fern. Generally, the leaves are straight and upright, with the entire leaf being about the same width until it tapers to a tip. The leaves can reach a maximum length of two feet and are split into several leaflets, or pinnae, that are uniformly spaced throughout the length of the leaf. The tint varies from pale yellowish green and dark green.
Kupukupu fronds are rigid and highly straight when growing in full sun and are often a lighter hue. Shade-grown plants have larger, darker-green leaves that may droop somewhat. In direct sunlight or moderate shade, the leaves frequently have spore-containing sori (plural, sorus) down the undersides of the leaflets. The term “Indusia” refers to the buildings that around the sori. The terms sori and indusia are frequently used to describe ferns. Nephrolepis species, such as the kupukupu, have kidney bean-shaped indusia (and sori) that run parallel to the pinnae’s mid-vein. The spores resemble fine dust and are dark or brownish in hue.
Kupukupu is a fern that spreads by tubers and stolons. Tubers are underground stems that have been transformed, whereas stolons are above-ground stems that have been changed. Both enable for vegetative proliferation of the kupukupu. Stolons crawl along the ground, forming new plants at their apexes. Tubers frequently remain dormant underground until disturbed, allowing the plant to regenerate if the above-ground plant is removed.
How to Grow Kupukupu Fern?
Kupukupu is a simple plant to cultivate. It thrives in either full sun or light shade. Its growth habit will vary slightly, as indicated above, depending on the location in which it is planted. While kupukupu is drought resilient, it favors damp conditions and thrives in moist soils. It grows in a wide variety of soil types, with the exception of beach sand.
Plant kupukupu plants 8 to 16 inches apart in a staggered arrangement to ensure rapid and complete cover. It is advisable to separate kupukupu plants from other crops, such as lawn grass, using some form of divider. Kupukupu will spread and become slightly invasive, however lawn edging will slow this process and make it easier to uproot any wayward plants that leap the edging.
Keep newly planted kupukupu wet to stimulate rapid proliferation and filling in of the space. As the plants mature, they will send out stolons to fill up any places that remain unplanted. When the area is entirely covered, reduce the amount of water applied. Natural rainfall should be sufficient to maintain kupukupu plantations thriving on the windward parts of the islands. Water kupukupu with around 1 inch of water every week on the leeward, drier areas of the islands to keep it green.
Kupukupu fronds do occasionally dry out and die, but the pinnae (leaflets) fall off quickly and the dead leaves are not visible. You may choose to remove dead midribs on occasion to trim older plants. Alternatively, you can prune the entire planter to around 4 inches in height and allow the young fronds to fill in. This can be repeated every couple of years to re-energize established plantings.
Kupukupu Fern Care Guide
Kupukupu grows pretty nicely in containers. They thrive in 8-inch or bigger pots and prefer to be contained inside them. Utilize regular potting mix and plant one or two tiny plants in each container to achieve maximum effect quickly. Stolons can be pushed back into the pot to develop additional shoots or clipped to give the potted plant a more manicured appearance.
Kupukupu is occasionally attacked by caterpillars. Use caterpillar-killing sprays or wettable Bacillus thuringensis (Bt) to control caterpillars. Ensure that the Bt you purchase is made specifically for caterpillars and not for other insects (such as mosquitoes). Bt works best when sprayed directly on the caterpillars, so ensure that the spray thoroughly covers the ferns when applied.
Kupukupu can be produced from spores, but the process is far more challenging than it is worth. Vegetative propagation of kupukupu is significantly easier. This can be accomplished in a variety of ways. The simplest method is to pluck plantlets that emerge at the ends of stolons before they become too firmly entrenched. Separate plantlets can be planted in individual pots or straight in the garden.
Another option is to use the subterranean tubers to propagate new plants. When kupukupu plants become pot-bound or fully cover a planting bed, tubers develop. They are often white and slightly fuzzy, but can be slightly green and smooth. They are roughly the size of table grapes. Tubers are most easily collected from a potted plant. Pluck the tubers from the root ball by removing the plant from the container. There are generally numerous around the periphery of the root ball, but if you want a large quantity of tubers, split the root ball and collect the tubers that grew in the middle as well.
Tubers can be stored for up to a week or two before planting, but they perform best if planted immediately. They should be submerged approximately halfway horizontally in wet potting mix. Maintain a moist potting mix and watch for plantlets to develop on one end of the tuber. When the plantlets reach a height of 2 to 3 inches, remove them from the potting mix (tuber attached or not) and place them in separate pots or directly into the garden.
Kupukupu is most effective when used as a ground cover. Once established, it will readily ward off weeds. It should be utilized as a ground cover in bulk plantings with or near taller plants. It will completely suffocate smaller plants.
Kupukupu is an excellent house or office plant. It enjoys bright light but may live under fluorescent lighting, albeit the fronds will droop significantly more than those of plants cultivated in direct sunshine.
The fronds are particularly effective in haku and wili lei. They may also be used as foliage in flower arrangements, however they will survive only a few days, if not a week. In previous times, Hawaiians utilized the fronds to decorate hula altars, signifying the sprouting of wisdom.
A word about nativity
According to a 2005 report, kupukupu are not native to Hawaii but were introduced and are only found from Cuba to Venezuela. However, the most recent version of the Bishop Museum and Smithsonian Institute’s checklist of native plants continues to list it as native to Hawaii. Thus, are kupukupu indigenous? Although the jury is still out, this is a fern worth cultivating.