How do I convert a RHS rating to Canadian?

Match the temperature range. RHS hardiness rating bands and Canadian plant hardiness zone bands are both defined by temperature, so a RHS rating maps onto whichever Canadian band or bands cover the same range. The match is usually approximate rather than exact, because the two systems divide the scale differently.

Do RHS and Canadian mean the same thing?

No. Plant needs at least this level of cold tolerance. Plant tolerates down to this zone. They are different claims, and reading one as the other is the most common cause of a plant being bought for the wrong climate.

RHS to Canadian — hardiness zone conversion table

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RHS hardiness rating is used in United Kingdom; Canadian plant hardiness zone is used in Canada. Both are anchored to temperature, so they can be lined up — but they divide the scale differently, and one band in one system often spans two in the other. Treat the table below as the nearest equivalent, not a precise translation.

They are not the same kind of claim. Plant needs at least this level of cold tolerance. Plant tolerates down to this zone. That difference matters more than the numbers: reading one as though it were the other is the single most common way a plant ends up bought for the wrong garden.

RHS to Canadian conversion table

Each RHS band against the Canadian band or bands covering the same temperatures
RHS	Temperature range	Canadian equivalent	What it means
H7	down to −20 °C	Zone 0, Zone 1, Zone 2, Zone 3, Zone 4, Zone 5	Very hardy — survives prolonged cold below −20 °C
H6	−20 °C to −15 °C	Zone 5, Zone 6	Hardy in a very cold winter
H5	−15 °C to −10 °C	Zone 6, Zone 7	Hardy in a cold winter
H4	−10 °C to −5 °C	Zone 7, Zone 8	Hardy in an average winter
H3	−5 °C to 1 °C	Zone 8, Zone 9	Half-hardy — needs sheltered spot or unheated greenhouse
H2	1 °C to 5 °C	Zone 9	Tender — protect from frost
H1c	5 °C to 10 °C	Zone 9	Warm temperate — outdoors only in mild areas
H1b	10 °C to 15 °C	Zone 9	Subtropical — frost-free conditions
H1a	15 °C and warmer	Zone 9	Heated greenhouse only

Why the conversion is approximate

RHS ratings run from H1a (greenhouse only) up to H7 (very hardy). Your local rating should be at or above the plant's rating to grow it outdoors.

Canadian zones are numbered 0–9 and run roughly one number lower than USDA at the cold end. The official system also weighs frost-free days, summer rainfall, summer maximum, snow cover and wind, so map values to your area using the official map for accuracy.

Because the two systems were built for different places and different questions, a converted number tells you roughly where a plant sits on the cold scale — not whether it will thrive. Summer heat, humidity, rainfall pattern and the length of your growing season all matter, and none of them appears in either rating.

Check a rating against your own conditions

Converting the number is only half the job. Cross-check a rating against your own climate, or find your zones in all four systems by answering a short set of questions about where you garden.

See also the full band tables for RHS hardiness rating and Canadian plant hardiness zone.