Highlighting winter winners and losers
Following the hard winters of early 2009 and 2009–2010, the RHS has undertaken a plant hardiness survey – and preliminary results have thrown up some surprising results.
RHS Chief Scientist John David collated results from an online survey of what survived, and he’s following it up this year by asking gardeners to email in findings in their own gardens.
David’s report found that during the cold spell in January and February 2009, plants such as rosemary have suffered, with parts or all of it killed. Many dahlias that were left out didn’t survive, yet cordylines, callistemons and oleanders, together with olive trees and certain palms, such as Phoenix canariensis and Butia capitata, have survived well in surprising places.
Background
The run of comparatively mild winters over the past 10 to 15 years was brought to an end by a period of cold weather, with the first appreciable snow fall, in the months of January and February 2009.
Temperature report - what happened where?
- Cold weather was most severe in southern England
- Unusually cold temperatures recorded in the south west
- Temperatures in northern England and Scotland were generally about normal.
- Over most of southern England, minimum night time temperatures reached -7 °C, with lows of -12 °C being reported inland
- Daytime temperatures did not rise above 0 °C for several days.
What really affects your plants?
The upsurge in popularity for planting half-hardy exotics and the influx of plants from warm temperate regions makes our survey particularly pertinent, but it also provides information in the context of global climate change.
The ability of a plant to survive cold weather varies according to the type of plant, and it not just down to where in the world it originally came from:
- Some plants from more tropical regions prove to be surprisingly winter hardy
- Others from much closer to home prove to be much more unreliable
- Plants that are older and better established are more likely to survive
- Plants over a certain age are more vulnerable - especially those from Mediterranean regions
Key factors
- Soil type
- The degree of moisture retention of the soil is critical
- Protection of the plant
- The ripening of the plant during the previous year
These factors go some way to explaining why a plant may have survived a lower temperature in one locality whereas it was more severely damaged, or even killed, by a marginally higher temperature elsewhere.
One other feature of plant performance is that while most plants will sustain some damage or will even regenerate when cut to the ground, others will just die and have little or no capacity to regenerate.
Hardiness survey – we reveal the winners and losers