Hardiness in plants is a tricky thing to gauge and it is difficult to tell people if a plant is completely hardy. So much depends on the location of the garden, the microclimate, the soil, the weather and the winter, as well as the provenance of the plants in some cases. A few years ago we all got a bit complacent after a succession of mild winters and then we had a reality check here in the UK and Ireland with a couple of severe winters that killed many plants that old books warned us were not reliably hardy.
Varieties of the same plant also vary hugely in their hardiness and these sages show this clearly. Last May/June I planted up two ‘beds’ with herbs; one with edible, shrubby herbs and the other with fragrant/colourful herbs. The beds were actually old, brick. ‘frames’ that I think were either for growing melons or other plants that needed protection, maybe violets or young plants. They were re-plastered and filled with sandy loam over rubble and mulched with 5cm of grit. It is the best-drained spot I could offer the plants. I am pleased to say that rosemary has grown well and the purple sage (Salvia officinalis ‘Purpurea’) is thriving as is the golden sage (Salvia officinalis ‘Icterina’). But there is a gap. This is where the much more delicate Salvia officinalis ‘Tricolor’ as planted. This is a much less vigorous plant anyway with smaller leaves that are a combination of purple, white/pink and grey. It is basically a variegated form of ‘Purpurea’ and it is almost as though the combination of colour is too much for the plant to cope with. It is certainly not as useful for cooking because of lack of vigour – the other two are fine for culinary purposes.
Golden marjoram (Oreganum vulgare ‘Aureum’) is a tough and beautiful plant and is as pretty as it is useful. The pink flowers later in summer are loved by bees.
There are some other gaps too. The lemon verbena (Aloysia citriodora) struggled on valiantly till about January and then looked as though it had given up – and it has!
Another casualty is the ‘French’ lavender ‘Raspberry Ruffles’. French lavenders (Lavendula stoechas) are popular because of the tuft of bracts at the top of the flower heads. They are not as pleasantly fragrant as the more common lavenders but that doesn’t stop people buying them – they are showy and beautiful. But as they are increasingly being bred in much warmer and drier climates – ‘Raspberry Ruffles’ is bred in Australia – I find that fewer have the ability to cope with cold and wet winters. The ‘Ruffles’ series are bred from the pretty tricky ‘Kew Red’ and is said to be two weeks earlier to flower than other varieties. It is said to be hardy to 5F which is -15 Celsius which seems very unlikely to me!
I am now pretty fed up with these showy French lavenders and I think that they should be treated as annuals or almost as bedding plants. The older, simpler varieties such as Lavendula stoechas ‘Willow Vale’, though less exciting, is much more likely to be more than a flash in the pan.