Dicksonia antarctica need over winter protection if temperature falls below freezing. The trunk and crown are the most important to protect, the fronds are able to quickly re-establish in the spring. The crown is the only point from which the fern is able to produce new top growth, so it’s important that it is not exposed to temperatures that will kill those tissues. The trunk is hardier than the crown, through the insulation it receives from the roots that cover it. The trunk does still need protecting to allow the flow of water and nutrients to the crown.
I always try and encourage people to leave the fronds intact over winter. Although they may get burnt by frost and turn brown they can are still useful to the plant. In the event that the winter is not as harsh as anticipated, any ferns that stay green will be able to perform photosynthesis giving the plant a boost of nutrients during the early growing season. If you choose to remove the fronds it will not cause major harm to the plant, but will mean that a new flush of fronds will have to emerge before photosynthesis can resume. The other benefit to leaving the fronds intact is in the spring the fronds will hang down and create a ‘skirt’ of dead fronds around the trunk. This can help the plant retain moisture, some people think this is tatty to me this is a tree fern in its natural state!
Here are some of our favourite methods of frost protection for Dicksonia antarctica tree ferns:
Garden fleece is now readily available from your local garden store. It can either be brought of a roll as a sheet or as a protective sleeve in different sizes. Using fleece is good as it allows the plant to breathe and is relatively easy to protect plants. If you have chosen to leave the fronds on I would advise you tie them up and then bend them over the top of the crown before wrapping the plant. You can use fleece to protect the entire length of the trunk but ensure you tie any fleece tightly around the plant to avoid the wind catching it.
You can use straw in a similar way to fleece. It also allows the plant to breath and won’t start rooting over one winter. If using straw make sure you lift and turn the straw a couple of times throughout the winter to make sure that crown is healthy. Don’t use hay instead of straw as this will degrade too quickly and encourage mould to grow.
The use of a structure to create a mini ‘greenhouse’ for bubble wrap is essential as the plastic will not allow the moisture around the plant in or out. The structure could be made out of bamboo canes or other material. You must consider how exposed the plant is and whether the structure is capable of standing up to wind is position will get. This method will take a little time but is worthwhile if you experience very harsh winters and want to protect a large plant in situ.
You can use leaf mulch in a similar way to straw. Leaf mulch is a natural protection, similar to the native growing conditions. Just make sure the leaf mulch is not packed to tightly or to wet. I would only use this method as a short term protection and not for the whole winter. If the leaf mulch is not removed it will continue to biodegrade and encourage rot.
Bringing plants into a greenhouse will give the best protection but being able to do this is a real luxury! The main thing to ensure is the plants do not dry out as they still need watering throughout the winter. The tree ferns I have in a heated potting shed overwinter are watered every 3/4 weeks.
Which ever method of protection you choose I always recommend checking your plant to make sure the crown is healthy throughout the winter and remove any insects that are nesting in the warmth.
Mature plants will become more tolerant over time, as they establish in their new micro climate. Also as the plant grows taller the crown is further from the ground where the temperature will be lower. Extra care will be needed for smaller plants. It is advisable to pay extra attention to any plants with a trunk of less than 1-2ft.