Guides · Climate zone
Zone 6b: what survives your winter
Winters to −20 °C (continental, mountain). Hardiness is the first filter on any plant list: a species below your zone is not a risk, it is a purchase with a date of death.
Zone 6b is a USDA hardiness zone: the average coldest winter temperature is around -20 °C. It does not tell you about summer heat, rainfall or wind, and it is not the only thing that matters — but it is the one that decides, on its own, whether a plant is alive in March.
Places we read as zone 6b: Upper Valais, Switzerland, Graubünden, Switzerland.
Two local corrections are worth making yourself. A city centre, a south wall or a courtyard runs half a zone to a full zone warmer than the open countryside around it. A valley floor where cold air pools, or an exposed plateau, runs colder. If your garden sits in one of those, use the neighbouring zone instead.
Hardy in zone 6b
15 species — 3 trees, 1 hedge, 1 shrub, 1 grass, 5 perennials, 4 edibles. Prices are French retail nursery prices per plant, 2026.
| Species | Type | Height | Spacing | Price | Why it belongs |
|---|---|---|---|---|---|
| Field mapleAcer campestre · Érable champêtre | tree | 8,00 m | 6,00 m | 165 € | The reliable small native canopy for heavy ground; takes clay and wind without sulking. |
| Snowy mespilusAmelanchier lamarckii · Amélanchier | tree | 5,00 m | 4,00 m | 145 € | Three seasons out of one small tree: white blossom, edible fruit, red autumn. |
| Sweet cherryPrunus avium · Cerisier | tree | 7,00 m | 6,00 m | 78 € | Prune only in summer: a winter cut on a cherry invites bacterial canker. |
| HornbeamCarpinus betulus · Charme | hedge | 2,00 m | 0,33 m | 6 € | Holds its brown leaf through winter and is the cheapest good hedge on clay. |
| Panicled hydrangeaHydrangea paniculata 'Limelight' · Hortensia paniculé | shrub | 2,00 m | 1,20 m | 18 € | The one hydrangea that takes real sun in the north and heavy soil everywhere. |
| Purple moor grassMolinia caerulea 'Transparent' · Molinie | grass | 1,40 m | 0,70 m | 11 € | One of the few good grasses for heavy, damp ground. |
| Hardy geraniumGeranium × oxonianum 'Claridge Druce' · Géranium vivace | perennial | 0,50 m | 0,50 m | 6 € | Covers ground under shrubs on heavy soil and asks for one cut a year. |
| Lenten roseHelleborus × hybridus · Hellébore | perennial | 0,50 m | 0,50 m | 14 € | Flowers in February under the canopy, when nothing else does. |
| Soft shield fernPolystichum setiferum · Polystic à soies | perennial | 0,70 m | 0,60 m | 11 € | Evergreen fern, unfazed by dry shade once its second year is past. |
| Wood sageSalvia nemorosa 'Caradonna' · Sauge des bois | perennial | 0,60 m | 0,40 m | 7 € | Flowers twice if you cut it back hard after the first flush. |
| YarrowAchillea 'Terracotta' · Achillée | perennial | 0,70 m | 0,50 m | 7 € | Flat heads that read well against grasses, and it does not need staking on poor soil. |
| Autumn raspberryRubus idaeus 'Zeva' · Framboisier remontant | edible | 1,60 m | 0,50 m | 7 € | An autumn variety is cut to the ground each February: no canes to tie in. |
| BlackcurrantRibes nigrum 'Andega' · Cassis | edible | 1,50 m | 1,50 m | 12 € | Fruits on last year's wood: take a third of the oldest stems out every winter. |
| Garden mintMentha spicata · Menthe verte | edible | 0,60 m | 0,40 m | 5 € | Only ever planted in a sunken pot. In open ground it takes the bed. |
| StrawberryFragaria × ananassa 'Mara des Bois' · Fraisier | edible | 0,25 m | 0,35 m | 4 € | Replace the plants every third year: yield halves after that. |
Not hardy in zone 6b
These want a milder winter than yours. In a pot that can be moved, or against a warm wall with sharp drainage, some will survive; in open ground they are a bet you will lose in a cold year.
- 01Olive (Olea europaea) — needs zone 8b or milder, so down to -9 °C, not -20 °C.
- 02Lavender (Lavandula × intermedia 'Grosso') — needs zone 7b or milder, so down to -15 °C, not -20 °C.
- 03Rosemary (Salvia rosmarinus) — needs zone 8a or milder, so down to -12 °C, not -20 °C.
- 04Cotton lavender (Santolina chamaecyparissus) — needs zone 7b or milder, so down to -15 °C, not -20 °C.
- 05Rock rose (Cistus × purpureus) — needs zone 8a or milder, so down to -12 °C, not -20 °C.
- 06Laurustinus (Viburnum tinus) — needs zone 8a or milder, so down to -12 °C, not -20 °C.
- 07Japanese holly (Ilex crenata 'Dark Green') — needs zone 7a or milder, so down to -17 °C, not -20 °C.
- 08Golden oats (Stipa gigantea) — needs zone 7b or milder, so down to -15 °C, not -20 °C.
- 09Autumn moor grass (Sesleria autumnalis) — needs zone 7a or milder, so down to -17 °C, not -20 °C.
- 10Japanese forest grass (Hakonechloa macra) — needs zone 7a or milder, so down to -17 °C, not -20 °C.
- 11Thyme (Thymus vulgaris) — needs zone 7a or milder, so down to -17 °C, not -20 °C.
- 12Mediterranean spurge (Euphorbia characias subsp. wulfenii) — needs zone 8a or milder, so down to -12 °C, not -20 °C.
- 13Silverberry (Elaeagnus × ebbingei) — needs zone 8a or milder, so down to -12 °C, not -20 °C.
We read your zone from your postcode as the first thing on the Brief, and every species in your Dossier is checked against it before it is drawn.