We advise planting Dahlia, Penstemon , Gaura and a few of the woody Salvia's such as Salvia Hot Lips after the frosts have past in late spring. These slightly tender perennials need to have time to get themselves well established in the garden prior to the onset of winter.
Gardeners employ various methods to make sure they can keep these plants from one year to the next -
- Taking cuttings and overwintering them in a greenhouse or on a windowsill - this is a particularly useful insurance policy if you grow Penstemon or tender Salvia
- Avoiding cutting plants back hard until the last of the spring frosts have passed.
- Covering plants with horticultural fleece during periods of frost
- Growing plants in pots so that they can be moved to a sheltered location overwinter and wrapping the pots in bubble plastic.
- Covering plants with a layer of protective mulch e.g. straw
What do we mean when we say a plant is tender?
In 2014 the Royal Horticultural Society devised new hardiness ratings for plants which we commonly grow in our gardens in the UK.
Of course the hardiness of a plant can be affected by a range of different factors, plants within one Genus such as Salvia or Penstemon, can range in hardiness from slightly tender to fully winter hardy. Every garden will have areas within it which are more protected from the prevailing weather conditions or become a frost pocket.
The RHS Hardiness ratings
All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets
- H1a - Under glass all year (>15C)
- H1b - Can be grown outside in the summer (10 - 15)
- H1c - Can be grown outside in the summer (5 - 10)
- H2 - Tolerant of low temperatures, but not surviving being frozen (1 to 5)
- H3 - Hardy in coastal and relatively mild parts of the UK (-5 to 1)
- H4 - Hardy through most of the UK (-10 to -5)
- H5 - Hardy in most places throughout the UK even in severe winters (-15 to -10)
- H6 - Hardy in all of UK and northern Europe (-20 to -15)
- H7 - Hardy in the severest European continental climates (< -20)
Read more about how the RHS hardiness ratings were devised