Red Mulberry

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.

NC State Extension Gardener Plant Toolbox, 'Actinidia arguta', plants.ces.ncsu.edu/plants/actinidia-arguta/ (fetched in-container 2026-08-31; READ BY THE MAINTAINER 2026-09-01): 'A male and female plant is needed for fruit production' - the dioecy this rule fires on - with the self-fertile exceptions named on the same page ('Issai': 'Self-pollinating, lower growing cultivar'; 'Chang Bai Giant': 'May fruit without male, more abundant fruit when male present'), and named male pollinizers ('Ken's Red': 'Male, used as pollinator'; 'Meader': 'Male pollinizer...'). [read]