Cultivation notes
Tree ferns thrive in a sheltered, humid and shaded position. They should be planted in humus-rich, neutral to slightly acid soil.
Extremely slow growing, these desirable plants only increase by about 2.5cm (1in) a year. Therefore, if you want a plant for immediate effect, you should choose a fern with a length of trunk that suits your planting scheme.
If you buy containerised ferns in leaf, plant at the same level as they were in the container.
Frondless lengths of trunk are also available. Plant just enough of the trunk to ensure the plant remains stable. After planting frondless tree ferns water every day until the foliage starts to emerge.
To encourage rooting, don’t feed the plant during its first year.
Watering and feeding
The trunk and crown of tree ferns will not tolerate drying out, so water regularly to ensure the trunk remains damp and spray the trunk with water during hot weather.
After the first year of planting, apply a dilute liquid feed to the fronds and trunk once a month, from mid-spring to mid-summer, when the plant is in growth. Alternatively, spread controlled-release fertiliser around the base of the plant in spring.
Winter protection
Although some tree ferns will survive all but the most severe winters, it’s best to err on the side of caution and protect plants to avoid damage to fronds. In mild gardens all you need to do is place a handful of straw in the crown, but more substantial wrapping is needed if you have a more exposed garden. In cold gardens tree ferns are best lifted and brought into a conservatory or greenhouse.
Propagation
If they produce them, tree ferns can be propagated from spores found on the underside of their leaves. However, cold temperatures or difficult growing conditions may inhibit spore production.
The easiest way to propagate tree ferns is from offsets. These are young plants that develop from the roots or trunk. Offsets develop slowly, so are best left to mature until they can be easily handled. Then do the following:
- Sever the offsets cleanly from the parent trunk or roots
- Pot them up in loam-based compost such as John Innes No 1 or 2, just deep enough so that they sit upright
- Water them in and place the pot in a propagator at 15-20°C (59-68°F) in bright but filtered light
- Once new growth shows, start to harden them off to outdoor conditions
Problems
Tree ferns are usually trouble-free, but may be affected by cold weather, woodlice living off decaying organic matter in the stems, and red spider mite, which can be a particular problem for plants kept under cover in glasshouses and conservatories.