I recently invested in a beautiful tree fern for our shady back garden. A gardening friend told me that I’ll need to give it some protection from winter cold to prevent it being damaged. Is this really necessary? DM, Dublin
Tree ferns have become very popular with Irish gardeners in recent decades, their dramatic silhouettes and stately presence used to add structure and drama as well as winter interest in the shape of their whiskery trunks and giant, arching, evergreen fronds. To see them growing at their impressive best in this country, pay a visit to Kells Bay Gardens in Co Kerry, which is home to a remarkable collection of towering specimens lovingly tended by owner and nurseryman Billy Alexander, some of them dating back to the early Victorian era.
Native to Australia and parts of southeast Asia, the hardiest and most commonly grown species is Dicksonia antarctica, whose cinnamon-coloured trunk is topped with a giant shuttlecock of finely cut fronds that are typically three to four times its height. Other very ornamental but less hardy species of tree fern include Dicksonia squarrosa and Cyathea dealbata. All are available to buy from Kells Bay Gardens’ nursery, along with many other unusual species of ferns (kellsgardens.ie).
Tree ferns are really only suitable for sheltered gardens in similarly mild, coastal regions of Ireland where harsh frosts are a rarity. Below minus 2C, the foliage will blacken and die back to the crown, while temperatures below minus 12C will generally kill them outright – hence their huge casualty rates after the fiercely cold weather that came with the Beast from the East.
Alexander advises stuffing a protective layer of pine needles into the crown of the plant (the point in the trunk from which the fronds emerge), which will offer protection from temperatures as low as minus 4C. Tree ferns like an acidic soil, so the pine needles serve a second purpose as a useful acidic organic mulch that helps to feed the plant. But if and when the forecast is for temperatures below minus 4C, then you’ll need to offer greater protection in the shape of several layers of horticultural fleece secured over the crown and fronds, making sure to remove this whenever temperatures rise to avoid weakening the plant.
[ Collecting ferns was like an addiction, I just kept collectingOpens in new window ]
Despite their reputation as shade-loving plants, tree ferns will grow quite happily in a sunny spot as long as they’re given protection from wind and cold, and an ericaceous soil (or an ericaceous potting compost, if grown in a large container). What they won’t tolerate is dry growing conditions. To keep yours happy, make sure to water it daily (twice that for newly planted specimens) and generously from March-October once temperatures reach above 10C, slowly drenching the crown of the plant as well as liberally wetting the fronds. A monthly liquid seaweed feed (again, directly into the crown) is also very beneficial.
