Giant dioon is the cycad that becomes a tree. It builds a genuine trunk over many years and carries long, arching, flat leaves made up of many leaflets edged with fine spiny teeth, which gives it a softer and more palm-like look than most of its relatives. It comes from limestone rainforest country in southern Mexico and behaves like a forest plant. Use it as a feature in a sheltered courtyard, or as the upper layer of a tropical understorey planting. Shelter while young, exposure once trunking It grows in full sun to part shade and takes low water once established, though the two ends of that range apply at different ages. Young plants want filtered light and shelter, because harsh sun on a soft new flush scorches the leaflets before they harden, and the damage stays on the plant for years given how long each set of leaves lasts. That is the failure mode here: buying a young plant, putting it straight into an open western position, and watching the first flush burn. Once the trunk is up and the crown sits above the surrounding planting, it takes far more exposure. Give it free-draining soil with organic matter worked through, steady moisture through the warm months, and never let it stand wet through winter. Plant into a raised or mounded bed if your soil holds water, and keep an organic mulch over the root zone through summer. It is comfortable in a large pot for many years, which also lets you move it as the light around it changes. All parts are toxic if eaten, so keep it away from dogs and grazing stock. Which cycad for which position Chestnut dioon is the same genus doing the opposite job, with stiff blue-grey fronds, a compact crown, an appetite for dry gritty soil and open sun, and far more cold tolerance. Take edule for an exposed gravel courtyard and spinulosum where there is canopy, humidity and shelter. Encephalartos whitelockii is the alternative if you want an arching crown as a standalone specimen and can give it warmth, though it is stiffer in the leaf and sharper to handle. Spinulosum is the pick when you want a cycad that eventually reads as a small tree. All three are slow, so the size you buy is close to the size you live with. It sits with our tropical plants. Leaf removal and steady feeding Remove leaves only once they have browned right through, cutting close to the trunk in spring, and leave the crown otherwise intact so the plant keeps the reserves it needs for the next flush. Never trim a full crown back to force new growth. Wear gloves, because the leaflet teeth are fine but they catch. Feed through spring and summer with a slow-release fertiliser formulated for palms and cycads, applied over the root zone and watered in, then taper off in autumn. Check the undersides of the leaflets as new leaves harden, since scale and mealybug settle there first and are far easier to control early.Choosing a sizeThis plant is available in 6 sizes, from 200mm up to 90L, priced from $38.95 to $1209.00 per plant. The size shown is the pot the plant arrives in, which is the rootball, not the height of the plant. The smaller pots hold younger plants that cost less each and establish quickly, which suits hedges, screens and mass planting where the plant count adds up. The larger sizes carry several more years of growth on the farm and give height and presence straight away, which is what you want for a single feature position or a screen that cannot wait. Not sure which to choose? Read our guide to when to plant in Australia.
