by Cynthia W. Mueller, Galveston County Master Gardener

Female Cycas revoluta. Image courtesy of Dr. Mike Arnold

Cycads (Cycas revoluta and others), often referred to as Sago Palms, have increased in popularity in Southern landscapes in recent years because of milder winters and because of their tropical looks and easy-care reputation. They are slow growing plants, which means that they are thought of as some of the more expensive, but permanent, residents of the landscape, so gardeners are often interested in increasing their stocks through rooting offsets or growing from seeds.

Dr. Bill Welch has grown and observed many of these cycads for years. He remarks, "The most common cycad for Texas and southern gardens is Cycas revoluta. Except for occasional cold damage sago palms are very tough plants. They cheerfully survive heat and drought but dislike wet, poorly drained sites. Their positive form and symmetrical leaf arrangement add a bit or formality to a garden. Cycads work well in containers but larger pots are best. For hardiness zones 8 and north be prepared to move them indoors or provide cover during cold spells. Other cycads useful for indoor or outdoor use include Zamia furfuracea, cardboard palm, Z. floridanum and Dion edule. All of these are less cold hardy than sago palms and are best grown where they can be protected in zone 9 and higher. Z. zamioculus has become more available in recent years and is popular for use indoors." Cycads are ancient gymnosperms that were typical plants of the Jurassic era, at the time of dinosaurs (about 150 million years ago). About 11 genera are included, comprising about 185 species. Even though they superficially resemble palms or ferns, they are related to neither.

Many times gardeners are fascinated by the pinecone-like 'megasporangium' that appears on mature plants, but are not quite sure what to do next to insure a crop of seeds.

The most important virtue for gardeners wanting to grow cycads from seed is - patience! Unlike many other plants in the landscape, cycads are dioecious, meaning that each one is either male or female, so that to get viable seeds both sexes need to be present, or at least one member of the opposite sex should be just over the fence in the neighbor's garden! This proximity is very important because small insects known as thrips (especially Cycadothrips chadwicki) move pollen from the male to female cones and are capable of squeezing through small openings in the cones to do so.

Thrips Cycadothrips chadwicki

When growing conditions are right, and the plants have reached a mature status, each sex will produce a megasporangium in its pithy, fibrous crown, some of which have been likened to a large pinecone or even an ear of corn.The male megasporangium contains clusters of microsporophylls containing pollen grains (microspores). Often these microsporophylls look surprisingly like individual segments of pine cones.

Cycads are unusual in that they generate both heat and strong, alluring odors in the microsporangia which are methods of drawing insects to investigate and distribute pollen. Dr. Irene Terry et al. (2) have reported that the temperature of a megasporangium may rise as much as 25F in mid-day during the receptive period. Graduated increases in odor are thought to drive the thrips into male cones, then back out again covered with pollen, which they take with them on visits to female cones, which are also capable of exuding an attractive scent. It was earlier thought that pollination was only achieved through windborn means, landing on drops of sticky material in the female cones which later dries, drawing the pollen into the receptacles. A period of time goes by while the pollen tube grows and develops, finally releasing fluid and sperm (which are motile), and which finally manages to enter the egg cell. Several months may pass between pollination and fertilization.

Working With Seeds: Dr. Severn C. Doughty described the sequence of events associated with the long event of embryo development in his article in Ornamentals South (1). As long as six months in some cases goes by while the embryo continues development. After the seeds are shed, the red, yellow or orange seeds/fruit may be eaten by animals, birds or bats, although the toxic seeds are usually quickly eliminated from the animal's system. Another period of waiting takes place while the embryos continue to develop and finally crack the hard seed coat. If the seeds are gathered by gardeners, the outer parts can be removed immediately, in case the coatings have an inhibitory effect on germination. Soaking for a day or so helps to soften the outer coat first.

Peel off the fleshy material around each seed with a sharp knife. If working with a large number of seeds, it may help to drop the cleaned seeds into a bucket of water overnight so that the heavier, fertile ones will sink to the bottom. Those with a lightweight or incomplete cotyledon will float and could be discarded at this stage. Individual seeds may be scarified, or scratched through with a three cornered file at the micropylar (pointed) end. After treating with fungicide the seeds may be buried to l/3 to l/2 the thickness of the seed in sterilized media such as sand, perlite, or a 50-50 mixture of perlite and peat. Periodically treat the soil media with more fungicide.

Temperatures between 75F and 90F are good for germination, and bottom heat is also beneficial. Allow the seeds to take their time. Pick out individual seedlings when they have one or two true leaves and repot in the same sort of medium and grow for two to three years under 40-50 percent shade cloth. After this the light can be increased to suit the species involved.

Leaf size, shape and "leatheriness" can often be manipulated by growers, with plants grown in stronger light usually being more compact in appearance.

Working With Offsets: Cycads may be increased through rooting the offsets that appear here and there on the trunk of the plant. If the shoots or offsets are from the base of the cycad, they may already have a few roots. These can be pried off carefully, let dry for a day or two, and dusted with sulphur or other fungicide. Then allow them to finish rooting in potting media.

If roots are not present, carefully cut the offset away with a sharp knife and let it dry for up to a few weeks till a callus has formed over the break. Dust the base of the offset and the wound in the cycad trunk with sulphur or fungicide to promote good plant health. A dusting of rooting hormone powder may also be applied. Then set the offsets into good potting media. If only a few leaves are attached to the offset, leave them. If leaves appear to be too numerous, cut away as many as 50%. Check occasionally for ongoing root development. Fertilize the developing suckers with a weak solution of a balanced fertilizer and plant them out when they appear to be thriving independently.

References:

1. Doughty, Severn C. History, Description & Culture of Cycads, Ornamentals South vol. 3 No. 3, pp 10-15, 1981.
   
2. Terry, Irene et al. Odor-mediated Push-pull Fertilization in Cycads. Science 318, no. 5847, p. 70, 2007.