La zona de rusticidad es la variable correcta para las perennes, y solo para las perennes.
Mecanismo: Las zonas codifican la temperatura mínima invernal media anual, que determina si una perenne leñosa sobrevive hasta la primavera. Es la magnitud equivocada para una anual, que nunca llega a ver el invierno. Una zona demasiado cálida es un segundo mecanismo, distinto. Los inviernos suaves no matan a una perenne; no le dan el frío que necesita. Los frutales caducifolios necesitan un periodo de latencia invernal para brotar y dar fruto, así que en una zona más suave que aquella a la que está adaptada una planta, esta puede sobrevivir y nunca producir. Solo se aplica el extremo frío, porque solo la supervivencia invernal se deduce de lo que mide una zona; el extremo cálido es un consejo, no un rechazo. Ese límite cálido pertenece a la variedad, no a la especie, y ese es el límite honesto de lo que esta regla puede hacer. El requisito de frío se publica por variedad y varía muchísimo dentro de una especie, así que un techo a nivel de especie dice "el rango modelado no llega a tu zona", nunca "ninguna planta de este tipo te dará cosecha". Por eso, por encima de su rango, el planificador sigue ofreciendo la planta, con el consejo de elegir una variedad clasificada para tu zona, en lugar de rechazarla.
Evidence: confirmed against 3 sources in the research-based literature.
the 3 sources
THE FLOOR IS TRUE BY DEFINITION and needs no citation: the USDA system defines a zone AS a band of average annual minimum winter temperature, so 'a plant colder-hardy than your zone survives your winter' is the definition restated. This rule was `verified_trivially` on that basis alone until 2026-07-26. THE CEILING WAS NEVER COVERED BY IT - a minimum-temperature definition says nothing about a plant failing for want of chill - and that gap is why ISSUES #13 exists. The pointer below closes it.
OSU Extension EC 1303, 'Growing blackberries in your home garden' (Bernadine Strik), catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/ec1303.pdf (read 2026-07-26). THE CEILING'S MECHANISM, STATED: 'Winter cold-hardy cultivars adapted to the colder regions of Oregon (such as zones 5 to 7), may not grow normally in regions of the Willamette Valley (zone 8) where winters are warmer and plants receive less winter chill.' A plant failing in a WARMER zone for want of chill - which is what this rule's upper bound enforces and what no source said until now. THE SAME PAGE MAKES IT A CULTIVAR PROPERTY: 'Even cultivars within the same type (trailing, erect or semierect) differ in fruit quality and flavor, appearance, tolerance to pests, cold hardiness, and plant longevity', and the remedy it gives is the one this rule's rejection text now repeats: 'Minimize risk by choosing types and cultivars that are adapted to your hardiness zone.' The page then publishes a table of sixteen cultivars EACH WITH ITS OWN ZONE RANGE, which is the strongest available evidence that a species-level band is an approximation. [read]
WHAT THIS DOES NOT SETTLE (amended 2026-09-24). The mechanism is named, but the corpus carries ONE band per species where the source carries one per cultivar, so the warm limit is explained without being precise. That is why, since 2026-07-26, the planner treats the warm end as advice rather than a refusal: above a species' band it still offers the plant and says to look for a cultivar rated for your zone, never that nothing will crop. Every species band now records what its sources say, though most are still marked estimated.