Tree Ferns in the UK

PimlicoDan
Published on January 26th 2020
11
tree ferns in a forest
Huge, prehistoric, reptile green and found in your garden: I can only be talking about one thing. No, not dinosaurs – tree ferns.
These majestic plants may have once been fodder for sauropods, but in recent decades they’ve become a popular, if somewhat pricey, addition to our gardens.
If you’re considering investing in one for your outdoor space, read on.
Tree ferns growing naturally in their antipodean forest home.

Is a tree fern a fern?

Yes. Tree ferns are true ferns. However, unlike most species which grow from a crown at ground level, these ferns produce impressive trunks. These trunks are not like that of a tree, but a rhizome (an underground horizontal stem) which grows vertically.
The most commonly-grown tree fern in the UK is Dicksonia antarctica, the soft or Australian tree fern. There are some other, less-frequently encountered species listed at the end of this article, though they are more tender.

Tree ferns in nature

In common with most ferns, tree ferns live in damp woodlands that have high humidity and shelter from rough, dry winds. They thrive in the cloud forests of Western Australia, where the air is saturated, and temperatures are cool and stable.
In the wild, tree ferns can grow to great heights – up to 15m – and have fronds (the leaves) which can form a canopy up to six metres across. Plants cultivated in gardens are generally smaller, a maximum two metres, but can still have quite an impact.
Mature tree ferns are often host to mosses, liverworts and other small ferns growing growing as harmless epiphytes on their trunks.

Why are tree ferns so expensive?

Tree ferns are expensive for several different reasons.
Tree ferns are not flowering plants. Instead, mature specimens produce tiny, dust-like spores. It then takes decades for the spores to grow into what we would recognise as an actual tree fern, as the trunks grow at a rate of around five centimetres per year.
Sometime small offsets will appear around older plants, which you can also propagate.
As tree ferns grow so slowly, you must use a responsible producer. In the UK, stock is obtained from certified, sustainable sources in Australia and New Zealand, so make sure to check.

How to grow a tree fern

Location

  • A damp, sheltered site in dappled, part or even full shade is preferred.
  • They will tolerate full sun, though will require more frequent watering.
  • The wind is a tree fern’s worst enemy, so avoid exposed sites.
  • Tree ferns will need winter protection in all but the mildest areas of the UK.
A group of palm trees on a leaf
A cool, shady and damp, sheltered spot will see your ferns produce large, healthy fronds.

Planting

  • In the UK, you can buy tree ferns in containers or just the trunk alone (usually with fronds removed).
  • To plant your tree fern, dig a hole that the plant can fit in with plenty of room.
  • In heavier soils, you may want to add leafmould for drainage.
  • Firm the plant in! Tree ferns may take several months to produce roots, so the trunk must be firm in the ground to avoid toppling.
  • Lastly, water the crown (growing point) of the plant and the top portion of the trunk. As the roots form the trunk, avoid the temptation to water at the base as with other plants. Water at least three times a week, if not every day, for the first six months and continue to water frequently after.
A plant in a garden
As you can see, this tree fern is in a relatively small pot with little growing media, as the roots used for absorption are mainly near the crown.

Overwintering

  • In warmer parts of the UK, such as Central London, the Scilly Isles and Cornwall, plants will survive unprotected during a mild winter. Elsewhere, they will need sheltering.
  • Younger plants in containers can be moved into greenhouses to save time. They may retain their fronds this way. Outdoors, plants will likely get blackened fronds as the colder weather hits.
  • Prepare your plants for winter before the first frosts arrive, usually from late October to mid-November.
  • Gently pack the crown with dry leaves or straw to protect the growing point. You can also put on a little fleece ‘cap’ to stop it from getting too wet.
  • For colder regions, or if the weather takes a turn for the worse, you can either:
  • Wrap the top portion of the trunk in fleece and bind in place with string;
  • Surround the top portion with chicken wire and pack with straw.
A close up of a statue
If in doubt, protect. Tree ferns are not fully hardy and are an expensive loss.

Troubleshooting

  • It can be a little nerve-wracking, removing the winter protection from the crown in spring. If the plant has been given enough protection, you’ll feel hard ‘knuckles’ on the plant. These are the fronds about to unfurl.
  • Squirrels have been known to nibble these knuckles, so if you have issues, cover the tree fern in chicken wire until growth begins.
  • If no growth occurs in the summer, the plant was likely damaged by cold or became too wet.
  • Dry fronds are usually down to underwatering or wind damage. Remember to place in a sheltered spot and give plenty of water (water the crown and trunk rather than the base). It’s impossible to overwater in the summer months!
A close up of a plant
The crown of a tree fern is the business end. Always water copiously in summer and protect during winter.

Other tree ferns

Although mild winters can tempt gardeners to grow alternative species outdoors year-round, only Dicksonia antarctica can be relied upon year-on-year. Several other tree ferns enjoy similar growing conditions, and if you live in a milder climate or have a cool greenhouse, they may be of interest:
Slender tree fern (Dicksonia squarrosa)
The slender tree fern is a shorter, narrower and neater version of D.antarctica. This tree fern will need to be moved undercover or be heavily protected over winter as it is only hardy to -5°C. The golden or woolly tree fern (D. fibrosa) is similar, but with lighter coloured fronds and hairier leaf stalks.
Silver tree fern (Cyathea dealbata)
The silver tree fern has bluey-green leaves with a silvery underside and a narrow, coarse trunk. Often considered to be one of the most beautiful tree ferns and depicted on the All Blacks rugby shirt. Only hardy to -5° when mature.
Lacey tree fern (Cyathea cooperi)
A fast-growing tree fern, but only half-hardy and will only possibly tolerate a light frost when mature. Probably best grown in a container where it can be placed outdoors for the summer and brought inside from November-April.
Dwarf Brazilian tree fern (Blechnum brasiliense)
This genus of tree fern is more frequently grown as a houseplant. Without a full trunk, this is a larger, hardier species than the indoor B gibbum. It beautiful, ladder-like fronds which begin copper in colour, changing to green as they mature. It is supposedly hardy to -5°C, although this is not very well documented.
The dwarf Brazilian tree fern is a stunning addition to a cool conservatory, forming a short trunk slowly over the years.

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