Phormium — New Zealand Flax

If there is any plant that adds year-round drama to a mixed border, decorative pot, poolside, or even a parking strip, it is Phormium. This evergreen perennial comes in all sizes with solid or variegated leaves that encompass a full spectrum of colors. Depending on the named cultivar, it can thrive in either sun or shade, tolerate coastal sprays and winter frosts, and be moderate in its thirst for water.

The genus has only two species, both of which are quite large: Phormium tenax and Phormium cookianum. However, it has a wide range of more garden-sized hybrids with distinctive leaf colors that are crosses between the two species, both of which are natives of New Zealand where they have been widely grown for their valuable fibers; hence the name, Phormium, which is Greek for basket.

Phormium tenax has stiff, sword-like, grayish green to bronzy green leaves up to 6-in. across marked with a thin line along smooth margins. Foliage rises 6-10 ft. tall and stretches 4-8 ft. wide as groups of leaves fan out on two sides from a central clump. In mature plants, sturdy stems bearing tubular, 2-in. flowers in rusty red or reddish orange rise high above the foliage.

Phormium cookianum can be distinguished by its somewhat smaller, curved outline. It displays medium-green leaves tinged with pink at their base, 4-5 ft. long and 2-3 in. wide. Some mature clumps can spread to 8-10 ft. or more. Yellow flowers appear on tall stalks in spring and summer, followed by long seed capsules. 

Unlike the stiff and vertical leaf structure of Phormium tenax, leaves on P. cookianum and its hybrids arch gracefully and droop slightly at their tips. However, those arching leaves are subject to sunburn if not given some afternoon shade, and this species tends to require more water than the more drought tolerant P. tenax. Pink and cream leaves are especially susceptible to sunburn.

As alluring as many of the phormiums are, mature plants can be half again as large as their nursery tags state and may outgrow their allotted garden space. An example is the beautiful maroon-red ‘Dusky Chief’ that was originally described as a medium grower at 3-4 ft. in height, but has turned out to be a much more vigorous 6-8 ft. clumper. When sited carefully, however, any of their spectacular forms is enhanced by a low-growing groundcover and adequate distance from neighboring plants.

Take care when planting to avoid setting phormiums too deeply and burying the crown, which can cause crown rot. Where gophers, moles, and voles are a problem, plant phormiums in wire baskets to protect roots. Phormiums are generally deer resistant but hummingbirds love the flowers despite their lack of showiness. Remove flower stalks when blossoms wither. Mealy bugs are their most common pest. Check for them between the leaves at the base of the plant. Remove by hand or treat with horticultural oil.

It is not uncommon for variegated leaves on Phormium hybrids to lose their bright colors, turn a dull green or brown, and revert back to their parent foliage. In this occurs, cut off the entire affected fan down to base of the clump.

Several hybrid species are notable for their bright colors or unusual forms. ‘Dazzler’ grows to 3 ft. or taller and 5-6 ft. wide with 1½ in. wide pink leaves striped in scarlet. ‘Sundowner,’  ‘Maori Chief,’ and ‘Maori Queen ’ can be breathtaking sights as the last of the sun’s rays filter through the arching leaves and capture the brilliance of their pinks, reds, greens and bronzes.

Several new hybrids have appeared in nurseries that are said to stay lower than 3 f t. Old favorites ‘Jack Sprat’ remains a proportionate 12 x 12 in. dwarf with spiky bronze foliage; ‘Thumbelina’ is somewhat larger.  

All phormiums develop multiple crowns that can be divided in the fall or early spring, ideally before a good rain, and transplanted elsewhere in the garden.  

December 2019