Winners and losers

Which plants are born survivors?

Exotic plants

• Agave americana (pictured above): hardier than expected with young plants surviving -7°C. Even the variegated forms, generally held to be more tender, seem to have survived similar temperatures, albeit with some leaf damage.
• Aloe aristata: commonly grown as a windowsill plant, this is known to survive cold temperatures. However the comparatively little known and altogether larger A. striatula has proved quite hardy and this year survived -7°C. It can regenerate if cut back to ground level.

South African foliage plant Melianthus major (left): Features in exotic plantings. Most reports were of it being cut to the ground, with only one report of it being killed outright, but no minimum temperature was recorded.

• Bananas: Now widespread in gardens and, like Melianthus, can regenerate if cut to the ground. One report of M. basjoo being killed when planted in the open and exposed to -9°C, and a report of it surviving uninjured by -7°C when wrapped in straw. Watch our video advice on overwintering bananas
• Isoplexis: the Canary Island foxglove relative lived up to its reputation for tenderness, but there is a difference between the species. At Abbotsbury, where a minimum of -6°C was recorded, I. canariensis was killed but I. sceptrum survived.

Echium: also suffered. The most commonly-grown in subtropical gardens is E. pininana - killed by -3°C in one garden - but E. wildprettii proved to be distinctly hardier. The hybrid between these two species, E. ‘Pink Fountain’, also appears to have gained a measure of hardiness from E. wildprettii.

• Hedychium species generally were cut to the ground. This winter confirmed that H. gardnerianum is decidedly tender, being killed outright by -5°C.
• Dahlia: A succession of mild winters beguiled many gardeners into leaving their dahlias in the ground only to find them killed as the frost penetrated the soil. There were, however, some survivals and, interestingly D. imperialis appears to have survived in two places after -6°C.

Palms

• Trachycarpus fortunei: long grown in UK gardens and accepted as reliably hardy in most places. In recent years gardeners have been tempted to try a range of other species. With palms, as with tree ferns, they become much hardier if they have a distinct trunk when planted. Many sold in garden centres are little more than seedlings – even if they look sizeable – and, as result, are liable to killed in cold weather.
• Other species of Trachycarpus are now being grown: the compact and decorative T. wagnerianus seems to be as hardy as T. fortunei, but the more elegant T. martianus has proved distinctly less so. Abbotsbury reported it to have been damaged by -6°C.
• Butia: This South American genus has shown great promise, with a mature plant of B. capitata having only leaf damage with -9°C, although a young plant was killed by -8°C but survived in Eastbourne, although no temperature was given. Abbotsbury reported no damage for other species, B. bonettii, B. eriophylla and B. yatay. A seven-year-old plant of the latter species was also reported to have survived -9°C.
• Phoenix canariensis: widely sold in plant centres and it certainly is the hardiest member of the genus. Larger plants and those given shelter have survived with some damage, but young plants were killed by -7.5°C when planted in the open.
• Washingtonia filifera: reported to have been killed in one garden with -9°C but survived the same temperature with leaf damage in another.
• Rhopalostylis sapida: Despite being the palm with the most southerly distribution in the southern hemisphere, this plant was killed by -6°C.

Tree ferns

Dicksonia antarctica: with the great popularity of tree ferns for gardens, there were quite a few records for this plant, which is the most widely grown species. By and large it lived up to its reputation for hardiness, with only one report of it being killed. Most reports stated that the leaves were lost with temperatures of -7°C or lower, but under milder conditions it was undamaged. With all tree ferns, as with palms, once there is a trunk the plant becomes distinctly hardier.

• Other tree ferns grown: Dicksonia fibrosa was reported as uninjured by -3°C [Report in The Pteridologist]. At Abbotsbury D. squarrosa was seriously damaged while Cyathea dealbata sustained only leaf scorch.
• Watch our video on caring for tree ferns

New plants

As with any of these surveys, some of the most interesting information is about plants that have been recently brought into cultivation.

• Gardenia jasminoides ‘Kleim’s Hardy: a much sought after gardenia that can be grown outside. There is only one report, but that stated that a young plant against a wall survived -10°C, although it was cut back.

Wollemia nobilis (pictured above): Perhaps one of the greatest surprises is how hardy this recently discovered and introduced member of the Araucariaceae from New South Wales has proved to be. It survived the cold remarkably well, showing little signs of damage. A small plant at Wisley planted fully in the open has come through undamaged.

• Schefflera taiwaniana: an interesting survivor out of a flood of new araliads coming in from China, all of untested hardiness.
• Evergreen magnolias, formerly known as Michelia: traditionally been thought of as plants for only the mildest gardens, as species such as M. doltsopa are at their best in Cornwall and Ireland. Some of the more recently introduced species, such as M. laevifolia (Michelia yunnanensis) and M. maudiae came through the winter of 2009 with little or no damage.

Mediterranean plants

Plants from the Mediterranean region are common in British gardens and, by and large, prove to be fairly resilient to our winters, partly because even in the Mediterranean they will occasionally experience quite sharp frosts.

What they do not experience is sustained cold weather, and it can be especially damaging when combined with damp conditions. In addition some Mediterranean plants are not long-lived and older plants will tend to be more vulnerable to climatic stress.

• Rosemary: proved to be more prone to damage or even being killed than might be expected, although most reports were of it being uninjured.
• Olive trees (Olea europaea) and oleander (Nerium oleander) are two plants from this region that have become more widely planted than in the past. With the protection of a wall both these plants came through temperatures as low as -11°C with some damage, whereas fully in the open they were cut to the ground or killed at -7°C.
• Myrtle (Myrtus communis, above left): proved to be on the tender side with loss of branches at -4°C and a young plant being killed by -9°C.
• Lavender: there were no reports of Lavandula angustifolia being lost but recent introductions of other lavender species have proved less reliable with L. × allardii and L. dentata subsp. candicans being killed by -7 and -12°C respectively while L. dentata was cut back by -5°C.

Southern Hemisphere plants

The Southern Hemisphere (Australia, New Zealand, S. Africa and S. America) is a source of many well known garden plants such as Eucalyptus, Callistemon and Acacia. As with other kinds of plants, there have also been some trials of less well-known plants such as Banksia and Protea. Results have been intriguing.

• Eucalyptus: almost all came through but one - E. globules - was killed outright by -8°C and E. leucoxylon ‘Rosea’ was cut to the ground by -9°C.
• Callistemon: while most species in cultivation were reported as uninjured, C. citrinus was cut back by -7.5°C.
• Leptospermum (pictured above): most species proved reliable but one - L. scoparium. There were reports of large plants being killed by -7, even though given the benefit of shelter.
• Acacia: mature plants seemed to be fairly hardy. Acacia dealbata, for instance, saw young plants cut back by -7 and killed by -8, whereas a mature plant survived -9°C with little damage.
• Banksia: less well known and being experimented with. B. marginata was found to come through -10°C uninjured, and B. grandis survived -6°C, although B. integrifolia was reported to have lost leaves at -10°C.

Protea cynaroides: This South African plant, pictured left, was cut back by -7°C and killed by -5 when grown in a pot.

Correa: also more widely grown and seems to have come through the low temperatures either uninjured or with slight damage. Correa ‘Ivory Bells’ survived -9°C while C. ‘Marion’s Marvel’ was cut back by -10°C as was Correa reflexa.