Beginners Guide to Cycads
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Although cycads are often grouped together with palms (e.g. Palm and Cycad Societies of Australia), they are actually completely unrelated. Cycads are in fact gymnosperms or coning plants (like pine trees), rather than angiosperms (flowering plants, like palm trees and most other plants). Gymnosperms are much older than angiosperms, first arriving on the scene about 240 million years ago (hence the common name of dinosaur food), while the angiosperms are much more recent arrivals. Gymnosperms are basically the link between ferns, and flowering plants. Prior to the arrival of the flowering plants, cycads were one of the dominant plant groups on the planet, and were distributed all over the land surface of the earth, however now their distribution is far more restricted (Central America, south and central Africa, Australia, and Asia).
Cycads are also dioecious, which means that they have male and female plants, (most plants are monoecious, or hermaphrodite, with both sexes on the same plant). Interestingly enough, it is impossible to determine the sex of a cycad except when it cones (these are its reproductive structures; males cones are long and thin, while the female cones are short and squat) i.e. we still don't know how sex is determined in cycads (its almost certainly genetic, but until someone throughs some serious money at the problem, it will remain a mystery).
General Cultivation Rules:
There are a couple of general rules for the cultivation of cycads, the first of which that they nearly all (with only a couple of obscure exceptions) like a very well drained potting mix. This can either be achieved by being carefull not to over water (the easiest solution), or if you have several plants, you can make up your own potting mix.
I use standard potting mix, to which I add @10% perlite, or polystyrene balls, to keep the mix open and free draining. In the ground they also require a well-drained position. The other thing that cycads like is deep pots, especially the seedlings. They can put down quite a long taproot that often gets bent around the bottom of ordinary sized pots. This root however, doesn't get longer as the plant grows, it usually just gets fatter, and forms an underground storage area for hard times, so that the larger plants are usually quite happy in ordinary shaped pots.
Commonly Grown Cycads:
Far and away the most commonly grown cycad is Cycas revoluta, often called sago palm. There are a number of reasons for its popularity, such as its attractiveness (it forms a medium sized plant up to 2m across, with very attractive dark green glossy leaflets), and its ease of growth (it is very forgiving, although it prefers full sun/light shade, in a moist, well drained position). It originally comes from some small islands off the south coast of Japan, where it grows on coastal cliffs. A plant that is becoming much more commonly available is C. thouarsii, a large and very vigorous grower from Madagascar. It will form a circle about 4 metres (12 feet) across, and its foliage has a distinctive bluish tinge. It likes full sun, and lots of water, but still demands a well-drained position.
Another commonly seen cycad is Zamia furfuracea, commonly called the cardboard sago, because of its very stiff leaflets. It comes from Central America. It forms a small clump, up to 2m across, and 1m tall, with very round, light grey/green leaflets. It also prefers full sun/light shade, in a well-drained position. Another plant from Central America is Dioon spinulosum, which grows to about 4m across, with quite spiny, light green leaflets. These plants come from limestone-based soils, so can be a bit pernikety on acidic soils (e.g. nearly all soils on the east coast of Australia, although it probably does quite well in Floridas's coastal soils).
Lepidozamia peroffskyana (often called Dinosaur Food in Australian nurseries) is also frequently seen in garden centres, and nurseries. It comes from south-east Queensland/north-east NSW where it is found in open eucalypt forest, on the edges of rainforest. Its forms a larger plant than those previously mentioned, getting up to 3.5/4m across. It also has very attractive dark green glossy leaflets, which get a nice bronzy tinge if the plant is grown in full sun. It also requires good drainage.
Bowenia serrulata, and B. spectabilis are also relatively common in nurseries, and are quite distinct from other cycads. They superficially look much closer to ferns than cycads, (they have branching leaves, and don't form the circular leaf arrangement of most other cycads), and like a shady, moist position (though again, it must be well drained). They make a very attractive understory plant.
Ceratozamia, a genus from Central America, aren't commonly found in nurseries, which is a great shame, because they are, by and large, easy to grow, and very attractive. They typically prefer light shade, and a moist well-drained position, although in areas of very high humidity, they can be grown in full sun. They are also quite tolerant of short cold snaps.
Encephalartos is a genus of cycads from south and central Africa, which are extremely popular with collectors, but this popularity has unfortunately kept prices relatively high, so they are rarely found in non-specialist nurseries. They tend to have very interestingly shaped dark green or "blue", spiky leaflets. These plants do grow very well in sub-tropical climates however, so if you do come across them, most make very worthwhile additions to the garden. The most commonly found is E. ferox, which likes a well-drained position, and (unlike most Encephalartos), prefers light shade. There are some highly prized "blue" species (with prices to match) (e.g. E. horridus, E. lehmannii) which are rather touchy (they come from desert areas, so like to be kept on the dry side). The blue colour is actually a coat of wax, which is a reasonably common adaptation found in desert plants to help protect the leaves.
Macrozamia is a genus confined entirely to Australia, and is very occasionally seen in nurseries. Again, they typically prefer full sun/light shade, and a well drained position.