Cold hardiness & minimum temperature

Is Franklin's Gem Boxwood (Buxus microphylla 'Franklin's Gem')cold hardy? Hardiness zone & min temp

Also called Franklin's Gem Boxwood.

More about franklin's gem boxwood

About Franklin's Gem Boxwood

Buxus microphylla 'Franklin's Gem' · also called Franklin's Gem Boxwood · flowering

Franklin's Gem is a compact Japanese boxwood prized for dense, rounded evergreen growth and strong resistance to bronzing in winter. It thrives in full sun to part shade, well-drained neutral-to-alkaline soil, and modest water once established. Slow-growing to about 60-90 cm, it shears cleanly into low hedges, edging, and tidy globes.

Cold limit: USDA 5-9 · RHS H6 (-23 to 30°C)

Watch for — Winter bronzing: Foliage can purple-bronze in cold, windy sun; 'Franklin's Gem' resists this better than most, but a wind screen or anti-desiccant helps in exposed sites.

What franklin's gem boxwood's hardiness rating actually means

Yes — franklin's gem boxwood is genuinely cold hardy. Rated RHS H6 and USDA 5-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H6 means: Hardy throughout the UK and northern Europe. On the US scale that maps to USDA 5-9 — the zones where it can be left outdoors year-round.

New to these scales? The USDA hardiness zone map explained covers how the zone numbers work, and you can find your own zone with the zone finder.

Minimum temperature — and what happens below it

Minimum survivable temperature is roughly about −20 to −15 °C. Franklin's Gem Boxwood is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for franklin's gem boxwood as it gets too cold:

It tolerates winter lows to about −20 to −15 °C once established.
Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root.
First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.

Can franklin's gem boxwood go outside or overwinter — and where?

Plant it out within USDA 5-9 and it overwinters with little or no help.
It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy.
The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

Work back from your local frost dates with the frost-date calculator: the last spring frost and first autumn frost are what really decide when franklin's gem boxwood can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Franklin's Gem Boxwood hardiness — frequently asked questions

Is franklin's gem boxwood cold hardy?

Yes — franklin's gem boxwood is genuinely cold hardy. Rated RHS H6 and USDA 5-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Franklin's Gem Boxwood is hardy across USDA 5-9; it belongs in the ground or a frost-proof container, not on a windowsill, and many types actively need a cold winter to perform.

What is the minimum temperature franklin's gem boxwood can survive?

Minimum survivable temperature is roughly about −20 to −15 °C. Franklin's Gem Boxwood is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is franklin's gem boxwood?

Franklin's Gem Boxwood is rated USDA 5-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can franklin's gem boxwood survive winter outside?

Plant it out within USDA 5-9 and it overwinters with little or no help. It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy. The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

What happens to franklin's gem boxwood below its minimum temperature?

It tolerates winter lows to about −20 to −15 °C once established. Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root. First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.