Cold hardiness & minimum temperature

Is Silkworm Mulberry (Morus bombycis)cold hardy? Hardiness zone & min temp

Also called Silkworm Mulberry, Japanese Mulberry, Korean Mulberry.

More about silkworm mulberry

About Silkworm Mulberry

Morus bombycis · also called Silkworm Mulberry, Japanese Mulberry · edible

A fast-growing deciduous tree prized for centuries as the primary food source for silkworms (Bombyx mori) and for its sweet, edible purple-black berries. Highly adaptable, tolerating a range of soils. Fruits ripen in early to midsummer and can be eaten fresh or used in jams, wines, and desserts.

Cold limit: USDA 5–9 · RHS H5 (-15 to 35°C)

Watch for — Bacterial canker (Pseudomonas syringae): Causes sunken lesions on stems and dieback of young shoots, especially after cold, wet spring weather. Prune out affected wood to healthy tissue, sterilise tools between cuts, and avoid overhead irrigation.

What silkworm mulberry's hardiness rating actually means

Yes — silkworm mulberry is genuinely cold hardy. Rated RHS H5 and USDA 5–9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H5 means: Hardy in most of the UK and in cold winters. 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 −15 to −10 °C. Silkworm Mulberry is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for silkworm mulberry as it gets too cold:

It tolerates winter lows to about −15 to −10 °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 silkworm mulberry 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 silkworm mulberry can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Silkworm Mulberry hardiness — frequently asked questions

Is silkworm mulberry cold hardy?

Yes — silkworm mulberry is genuinely cold hardy. Rated RHS H5 and USDA 5–9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Silkworm Mulberry 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 silkworm mulberry can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. Silkworm Mulberry is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is silkworm mulberry?

Silkworm Mulberry is rated USDA 5–9 and RHS H5 — Hardy in most of the UK and in cold winters.

Can silkworm mulberry 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 silkworm mulberry below its minimum temperature?

It tolerates winter lows to about −15 to −10 °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.