Materials such as fleece, hessian, bracken, straw and polystyrene can be used to insulate plants from cold or wind. To prevent sweating and possible rotting, protective covers should be removed when extended periods of very mild weather are forecast, but replaced as necessary if the weather becomes cold again.
Tender climbers such as Eccremocarpus, Passiflora mollissima and Solanum jasminoides are trained against warm walls to give them protection, but also benefit from having their lower stems packed with straw or bracken in winter. This is held in place with fleece, netting or hessian wrapped around canes and secured with string, wire or garden twine.
Examples of shrubs that may need wrapping include Pittosporum tobira and Cestrum. In cold or exposed situations, borderline hardy plants such as Callistemon, Clerodendrum bungei, Clianthus puniceus and Pittosporum tenuifolium may also need protection. Figs are wrapped to protect the embryonic fruits even though the plant is hardy.
Smaller specimens can be protected by constructing a rigid frame or wigwam of bamboo canes around the plant, packing around with bracken or straw and covering with netting. In wet periods, temporary waterproof cover should be added, wrapping clear polythene over the whole structure to prevent it getting wet and rotting.
Larger specimens can be surrounded with a 5-7.5cm (2-3in) layer of bracken or straw sandwiched between sheets of wire netting. A detachable lid can be placed on top in very severe conditions.
Shrubs growing against walls can be packed with straw or bracken behind and around the branches. A batten can be fixed to the wall above the plant with fleece or netting suspended from it, hanging down like a drape over the plant. A batten at the bottom of the drape allows the covering to be rolled up in mild weather.
Wrapping tree ferns
Tree ferns in mild, sheltered areas may be fine with a packing of straw over the crown and a polystyrene cap to keep off the rain, but in colder areas complete wrapping is recommended. The trunk is easily wrapped in fleece. The fronds should be tied upright with straw or bracken packing at the centre, and the whole bundle wrapped in a double layer of horticultural fleece. The root area is mulched with organic matter to protect the roots from frost.