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Curcuma - Hidden Cone Gingers for the Temperate Garden

To get a bold-textured tropical look in a warm temperate garden, there is a short list of exotic plants that fit the bill. One of my favorites is the little-known but amazing genus Curcuma. Curcuma, or hidden cone gingers, is a genus of mostly tropical plants known for their dramatic bold foliage, flamboyant floral show, and in the case of Curcuma longa, as a culinary spice. Curcuma can range in height from just under 2' to over 7' tall. The slightly hidden flowers resemble psychedelic pinecones...a nice trip back to the 1960s. We urge our readers to visit the garden on our Open Nursery and Garden Days in summer and fall to see our Curcuma collection. One of the reasons that Curcuma have never reached a high level of popularity is that they haven't begun to sprout during the spring garden center season, but because of this, they can be interplanted with spring bulbs such as daffodils, which go dormant before Curcuma emerges. Curcuma are plants that you must purchase as a leap of faith, then sit back and enjoy later in your garden. 

 

How to grow Curcuma...Grow your own Turmeric Plant!

In their native habitats, Curcuma emerge during the monsoon season and are triggered to become dormant by dry weather. This roughly corresponds to the winter/summer cycle in temperate gardens. Ginger expert, Tony Schilling, says "treat them to monsoon conditions - warm, wet and well fed in the summer, and cool and dry in the winter." If you let your Curcuma get too dry, they will lose their leaves and stop flowering. Moist, but well-drained, organically-rich, slightly acidic soils produce the best flowering. Curcuma prefer sun for at least a couple of hours, but most species will also do fine in high, open shade.

We have also found that Curcuma will perform best if lifted and divided every 5 years in order to maintain their vigor. In doing so, keep in mind that if you divide the plants when they are too small, they may not flower for a couple of years. At a minimum, leave 3-5 eyes (the creamy pointy things) per division, but more is better. Dividing is best done in spring or summer. When re-planting, place the rhizomes 4-6" below the surface to give them some cold protection, although the rhizomes will eventually grow to the depth that best suits them.

After frost kills the tops, you may cut back the stems and compost them or leave them alone and the stems will detach from the rhizomes naturally. In climates where the Curcuma aren't winter hardy, lift and store the rhizomes inside in a box of sawdust or peat moss (to prevent desiccation) where the temperatures stay above freezing.

Curcuma also make great potted plants, however, gardeners will need to re-pot the plants often because the thick rhizomes quickly grow large enough to split open a pot. Potted specimens require lots of water (daily or even more frequently) when they are active and root-bound.

Curcuma Pests and Diseases (aka: Ginger ailments)

Luckily, Curcuma are not bothered by many pests, with slugs and snails being the worst…especially on the unfurling leaves. In containers or in a soil that is too dry, mealy bugs and spider mites may become a problem. In old plantings, a fungal disease called mushroom root rot may occur. The first symptom is the browning and loss of the top few leaves on the stem. If you cut open a rhizome and find brown flesh with white specks your plant probably has root rot. Cut off all of the infected parts of the rhizome, dust the remaining healthy parts with sulfur powder and replant in a new location. 

 

How to Propagate Curcuma

Most Curcuma are sterile, leading to the current assumption that most plants in the trade are hybrids, so don't expect to see any seed unless you have access to wild collected species. In the wild, specific Curcuma pollinators are also present that are not present in the temperate garden. Thus Curcuma will not set seed in the garden unless you hand pollinate them during the summer. If you manage to actually get seed, they are relatively easy to germinate. Seed should be collected as the seed pods open in the late fall and must be surface sown (don't cover) immediately. The seed may take several months of warm temperatures to germinate.

Curcuma History - Ethnobotanical and Economic uses - Curcuma longa and Turmeric

Cultivated for more than 4000 years for the spice turmeric, Curcuma longa rhizomes have been a source of food, spice, and medicine...so many uses that Turmeric is sometimes called the world's healthiest spice. Curcuma longa rhizomes are dried and ground into the spice turmeric which gives curry powder its distinct yellow color and odor. Turmeric has several purported medicinal uses including reducing inflammation, lowering blood pressure, slowing down Alzheimer's disease, and relieving pain. Turmeric is quite popular in traditional chinese medicine and with western herbalists and health nuts. The rhizome of Curcuma longa is also a source of a dark yellow dye used in cosmetics and food coloring. Another species, Curcuma amada, has rhizomes that are eaten fresh and used as both anti-inflammatory medicines and contraceptives. Curcuma zedoaria rhizomes are eaten as a spicy, but bitter vegetable, and are also used to combat flatulence…move over Beano®. Oils from Curcuma are used in perfumes and, of course, many Curcuma are grown as cut flowers. As gardeners discover that many of the curcuma species are winter hardy, there is tremendous growth potential in this market as well.

Curcuma Morphology

Curcuma is a deciduous herbaceous perennial with thick, fleshy, branched rhizomes. Their "stems" are not true stems, but actually pseudostems, because they are composed of long, succulent, interlocked leaf petioles from which the leaves arise. Pseudostems with clasping leaves are common in this group of plants and can also be seen in both canna and bananas (Musa, Musella, Ensete). All the genera in the family Zingiberaceae have food storage rhizomes with a "gingery" or "lemony" scent. The leaves, which are similar to a canna, can be solid green, variegated, or have a red central blotch.

Curcuma have flower spikes that arise from the top of the pseudostem or sometimes on a separate stem directly from the rhizome. Flowering may occur early in the growing season, just before the leaves unfurl or along with them late in the growing season, depending on the species. The bracts near the top of the spike are colorful and showy, but do not have florets. The florets are held lower down on the spike amongst less-showy bracts. Like poinsettias, the actual flowers are not the featured attraction. The florets are white, yellow, pink or orange in color and the bracts can be a variety of colors including white, pink, yellow, green, burgundy, or multicolored. The overall effect is that of a technicolored pinecone. Curcuma need heat to trigger flowering and thus do well in warm climates such as the Southeast US. In mild climates (like Great Britain) Curcuma may grow well but never bloom.

Although Curcuma come from warm parts of the world, they go through a dormant period in which the plants die back to the rhizome and then are slow to re-emerge in the spring. Many gardeners assume that they have lost their plants but are relieved to see them finally emerge in June and July when the soil temperatures heat up.

Curcuma Taxonomy

Curcuma belong to the ginger family Zingiberaceae, which includes many useful herbs and ornamental plants. The spice, ginger (from Zingiber officinalis), is the best known and most widely used. Important ornamental cousins include Alpinia (Shell Ginger), and Kaempferia (torch-ginger). The gingers are more distantly related to other common ornamental plants such as Musa (bananas), Heliconia, Canna, and Maranta. All Zingiberaceae share a common trait in that their flowers produce just one true stamen.

The genus Curcuma consists of between 80 and 117 species of medium-sized plants. Their center of diversity is in southeast Asia, but some species extend to the Himalayas, Southern China, Australia and the Pacific Islands. The name Curcuma was coined by Carl Linnaeus and refers to the Arabic word "kurkum" which is their name for the yellowish color of the root.

Curcuma are commonly known by a number of common names, including turmeric, Indian saffron, Siam tulip, zedoary, and hidden lily. The first two names refer to its use as a spice and the name "hidden lily" refers to the fact that some species have short inflorescences that are obscured by the leaves.

List of Curcuma Species, Cultivars, and Hybrids

Below is a list of some of the interesting species and cultivars that have been successful at Plant Delights Nursery and Juniper Level Botanic Gardens. There are many more possibilities available for gardeners from Zone 8b and south. Recent genetic work in Curcuma is showing that many of the plants which we think of as species are actually ancient sterile hybrids…that work continues while we strive to find species that tolerate our central North Carolina climate (Hardiness Zone 7b, 35ºN latitude).

Curcuma elata (Spring Hidden Cone Ginger) has stood out in our trials as one of the finest cold-climate garden specimens in the genus Curcuma. The huge, bold-textured, canna-shaped green leaves compose the giant 6' tall clump. For us, this is the earliest Curcuma to flower, mid-June in NC, when the 1' tall pinecone-like spikes sprout from the base of the plant. Each flower spike is topped with bright pink bracts which serve as mini-umbrellas for the yellow flowers that poke from the side of the cone below. (Hardiness Zone 7b-10 at least). 

Curcuma longa (Turmeric) (syn. Curcuma domestica) is one of the toughest Curcuma that we grow. The 3' tall pleated green leaves of Curcuma longa are adorned, starting in early September, with colorful pinecone-like flowers that are nestled among the leaves. (Hardiness Zone 7b-11)

Curcuma myanmarensis (Burma Pink Hidden Cone Ginger)(aka: Smithatris myanmarensis) is an amazingly hardy and floriferous hidden cone ginger. Curcuma myanmarensis hails from Burma (Myanmar), where it forms slowly multiplying clumps in the moist woodlands. In the garden, the central stalk is adorned by two light green leaves, then topped by a terminal 18" tall stalk that ends in a short pink torch. Curcuma myanmarensis is the longest flowering ginger that we grow, with flower stalks being produced from late spring into October (NC). Curcuma myanmarensis is an easy-to-grow sister to the more difficult and less hardy Curcuma alismatifolia. We recommend planting at least 6" deep if your soils are prone to freezing in the winter. (Hardiness Zone 8-10 guessing)

Curcuma ornata (Ornate Hidden Cone Ginger) has a tropical appearance in the border or in a color bowl. It's hard to beat this Asian species, which resembles Curcuma zedoaria, except that the leaf is much larger: 28" long and 8" wide. Each textured green leaf has the same fabulous reddish purple stripe down the center. In addition to the larger leaves and larger stature of the clump, Curcuma ornata has a reddish purple cast to the lower stem. The hidden pinecone-like flowers of light pink are attractive for nearly a month in June. (Hardiness Zone 7b-10 guessing)

Curcuma petiolata (Hidden Cone Ginger) has large, tropical looking leaves (10" long by 6" wide) that form a 3' tall clump. The foliage grows out of a short underground rhizome, making an upward growing small clump. The flowers resemble purple pinecones and are formed in the middle of the clump from mid-to late summer. (Hardiness Zone 7b-10 guessing)

Curcuma petiolata 'Emperor' (Striped Hidden Cone Ginger) This Tim Chapman introduction from Thailand makes an easy-to-grow, 2' tall by 2' wide clump of pleated green leaves (18" long by 6" wide), each with a dramatic white border. This is the only known variegated curcuma. In early summer, you will enjoy the pinecone-like flower of purple and green at the base, and for the rest of the growing season you will adore the tropical foliage. It has survived 0 degrees F in our garden with no protection, but in colder climates it makes a great house plant. (Hardiness Zone 7b-10) 

Curcuma zedoaria (Hidden Cone Ginger) is a spectacular ginger that garners all the attention from our visitors...especially since it has survived 0 degrees F in our garden. The large, tropical-looking green leaves (2' long by 5" wide) have a dramatic, wide, purple-red stripe down their centers. As the leaves emerge, so do the flowers, resembling oversized '60s psychedelic red-and-yellow pinecones on 1' scapes. Each plant makes a clump to 3' (taller in warmer climates) by 2-3' wide. (Hardiness Zone 7b-10)

Curcuma zedoaria 'Bicolor Wonder' (Bicolor Hidden Cone Ginger) was selected for its attractive bicolor flowering bracts...solid white except for purple fingernail-sized tips on the end of each bract. The 6' tall, bold, aspidistra-like foliage, with a maroon stripe down the leaf center, emerges in mid-June alongside the pinecone-like inflorescence. (Hardiness Zone 7b-10)

Curcuma zedoaria 'Pink Wonder' (Pink Wonder Hidden Cone Ginger) The foliage of this selection resembles a fancy aspidistra on steroids...6' tall green leaves with a central burgundy stripe. The flowers on this selection emerge like pinecones on separate 1' tall stems alongside the foliage. Curcuma 'Pink Wonder' was selected for inflorescences that are white at the base and bright pink on the top. (Hardiness Zone 7b-10)

Curcuma zedoaria 'White Wonder' (White Wonder Hidden Cone Ginger) The 5' tall pleated green leaves, without the maroon stripe, are adorned in fall with pure white "cones". (Hardiness Zone 7b-10)

List of Curcuma Hybrids

Curcuma 'Pink Plush' (Pink Plush Hidden Cone Ginger) This is a wonderful Tom Wood hybrid. The 30" tall clump is composed of long green leaves, each highlighted by a central purple stripe. The clumps are adorned with 1' tall stalks of lovely pink pinecone-like flowers from late August into October. So far, this has survived 8 degrees F with no protection. (Hardiness Zone 8-11)

Curcuma 'Sulee Sunshine' (Sulee Sunshine Hidden Cone Ginger) is a hybrid from Thailand breeder Annop Ongsakul. Developed for the tropical cut flower market, Curcuma 'Sulee Sunshine' has come through two mild winters (15ºF) in our garden. This splendid selection flowers for us from August through October with 9" stalks, topped with long-lasting 8" flower "cones," dipped in pink and yellow. As a background, the 18" long by 8" wide pleated green leaves naturally fold away from the flowers unlike many of the other curcumas. (Hardiness Zone 8-10 at least)

Curcuma 'Summer Snow' (Hidden Cone Ginger) The green leaves only reach 3' in height, adorned by the cone-shaped flowers which are nestled about 2' off the ground in September. (Hardiness Zone 7b-10)

References

Branney, T.M.E. (2005), Hardy Gingers including Hedychium, Roscoea, and Zingiber, Timber Press, Portland Oregon

Chapman, T.S., (1994), Ornamental Gingers - A Preliminary Guide to Selection and Cultivation

Constantine, D., (2008), Hedychium, an annotated list of the species and cultivars grown in the UK, http://www.users.globalnet.co.uk/~drc/hedychium_home.htm

Plant Delights Nursery and Juniper Level Botanic Garden - Gardening with Hardy Tropicals

Ravindran, P.N., et. al., (2007), Botany and Crop Improvement of Turmeric, in Turmeric: the genus Curcuma, 1st Edition, CRC Press

Spencer-Mills, L. & K. (1996), Glorious Hedychium, The Garden magazine, December 1996, pp. 754-759

Wood, T. (1999), Ginger Lilies, The American Gardener magazine, November/December issue, pp. 40-45.