Be among the first to grow the unusual and drought-tolerant mao, or Hawaiian cotton, in your garden. The plant is an endemic Hawaiian species. Mao is rare in the wild today although it was once well-established in dry, coastal locations on many of our islands for centuries, even before contact. Coastal development has greatly reduced its numbers in the wild, but it grows well in cultivation and can add beauty and interest to a garden setting.
Gossypium tomentosum is similar in some ways to other members of the genus. The generic name is derived from the Greek word for cotton, gossypion. All plants in this genus are in the Malvaceae, or Hibiscus family. The Hawaiian cotton species name, tomentosum, is derived from the Latin tomentosus meaning “covered with tangled or matted, woolly hairs.” It is well named as the fruit that follows the flowering of mao plants is definitely a boll of woolly hairs. The “woolly hairs” of mao are usually not white like its cousin, Gossypium hirsutum, which is known as upland or Mexican cotton and is native to Central America. G. hirsutum is responsible for 95 percent of all cotton fabric production today.
Genetic studies indicate that the Hawaiian cotton is a close relative of the Mexican species. Mao’s ancestors may have come to the islands from Central America as seeds on the wind, on the wings or droppings of birds or on the waves as floating debris. Once they arrived, they developed several genetic differences but the close relationship to other cottons has made Hawaiian cotton very important in the industry. Mao is genetically resistant to some diseases and pests of commercial cotton and through careful breeding programs has offered its resistance to the worldwide cotton crop.
G. tomentosum is a shrub that grows from 18 inches to 6 feet tall and can spread laterally, forming clumps up to 10 feet wide. Mao has silvery-green leaves that are 3 to 5 inches across with 3 to 5 lobes, similar to those of some hibiscus plants. The silvery-green color comes from the presence of tiny soft white hairs on the leaves. This feature and coloration is usual in drought-tolerant species.
Mao is a prolific bloomer producing bright yellow, hibiscus-like flowers up to 3 inches in diameter throughout the year. The bracts of the flowers are sharply toothed and stay in place to enclose the fruit and seeds which follow the flowers. The fruit is enclosed in a three-part capsule that dries and becomes woody before breaking open to reveal about a dozen small black seeds covered with the reddish brown fibers we call “cotton.” Mao provides visual interest in both the flowering and fruiting phases of its growth.
The flowers as well as the dried fruit capsules and seeds can be used for lei making or in dried arrangements. The flowers of mao also produce a green dye traditionally used in kapa production. The name mao comes from the Hawaiian word for green — omaomao. The woolly fibers of the fruit were occasionally used for stuffing bedding but the fibers are far fewer than those on a true cotton plant. The seeds can also be processed to produce cottonseed oil.
The seeds are the best way to propagate mao. Most propagators recommend scarification of the tough seed coat before planting to improve germination. This can be done by actually nicking the seed coat with a knife or nail clippers or by soaking the seeds in water for about 24 hours to soften the coat before planting. Plant the seeds in a sterile planting mix for best results. Place the pots in light shade and maintain moisture until the plants are large enough to move to their final location. Be careful not to overwater.
Mao can also be propagated from cuttings or by air layering. These techniques are a bit more complicated, take longer and are not as foolproof as seeding.
Hawaiian cotton is actually a perennial shrub that can be used for borders or hedges or as an interesting specimen plant. The plants grow best in hot, sunny areas and only need occasional watering. They are very wind and salt tolerant but do not do well in areas with high rainfall or wet soil. They can be short lived unless conditions are optimal and will occasionally die in three to five years. They can be replaced if you save the seeds.
Occasional fertilization and mulching can extend the life of a mao plant and periodic pruning may be necessary to control the height, keep the shrub full and to prevent spreading.
Though problems from chewing insects, scale, mealy bugs or nematodes may occur sporadically, all are easy to treat and avoidable if the plants are kept healthy.
The Amy B.H. Greenwell Ethnobotanical Garden often has Hawaiian cotton plants for sale. Call them at 323-3318 to see if they have them or know where you can acquire them. Calling around to local nurseries, you may find other sources as well.
Planting and growing endangered native Hawaiian plants like mao can help keep them from extinction while providing you with interesting plants for your garden.
Diana Duff is an organic farmer, plant adviser and consultant.