There are three main strategies for providing overwinter protection to tree ferns: keeping them in a conservatory all year round; overwintering small plants in a protected environment; and protecting larger plants outdoors in situ. Deciding which strategy is right for you will depend on several factors including the plants location, position and species.
Dicksonia antarctica is the most commonly grown specimen outside of warmer climates. It can be described as hardy down -10°C but this shouldn’t be taken for granted. Where temperatures dip below -2°C some protection to plants should be considered. Other species vary on how tolerant they are to cold climates. Cyathea australis and Dicksonia fibrosa can be considered nearly as hardy as Dicksonia antarctica and should be protected in a similar way.
Mature plants become more tolerant over time, firstly because they are more established as a plant and have more protection around key areas and secondly 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. Where possible it is advisable to bring any plants with a trunk of less than 1-2ft into a cool conservatory, greenhouse, or even a shed, to offer it more protection. It is also desirable to cover the plant with fleece on those nights with hard frosts for added protection, but remember to continue water the trunks once or twice a month.
Larger plants, although more hardy, still need some protection. The easiest way to provide this is to is to compact a good amount of straw in the crowns of the ferns to stop ice from freezing the crown. In plants less than 4ft added protection may be necessary by insulating the trunk with polystyrene plants trays secured around the trunk.
The main thing with larger plants is to ensure that there is sufficient protection to the crown, but also to ensure the crown can breathe so it does not root. Some people will loosely place straw in the crown and it is important to check a few times over winter to clear any wet fallen leave from the crown.
If you are unsure as to which is the right fern for you keep check our Growing Tree Ferns page for more advice.