Four Season Greenhouses
indoor climates for year-round abundance

A four-season greenhouse can be as simple as a High Tunnel or a Growing Dome, or as complex as a custom building with a foundation and automated controls.  The choice depends on the number of "hardiness zone steps" you want to make, between your outdoor climate and the indoor greenhouse climate you want to create.  For example, a simple insulated hoophouse with no solar heat storage or backup heat, may enable you to grow zone 7 - 8 greens and cold hardy vegetables, through a zone 4 winter outside, representing a 3 - 4 "zone-step".  At the other extreme, it will require an insulated foundation, solar heat storage system such as a climate battery, and an energy efficient enclosure with some form of backup heat, to grow zone 11 - 12 tropical perennials indoors, with a zone 4 winter raging outside, a "7 - 8 zone step".
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Row Covers inside a high tunnel greenhouse provides a "3 zone step", in this case creating a zone 8 climate within a hardiness zone 5 climate.
Elkstone Farm, tropical house capable of an "8-zone step" in Steamboat Springs Colorado, raising bananas, papayas, and citrus, year-round.
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A custom 4-season house with insulated north roof, east, north and west walls, and a full climate battery, creates a "7-zone step".
Central Rocky Mountain Permaculture Institute - Phoenix Greenhouse - an "8-zone step" on renewable energy alone.
a slide show gallery of 4-season greenhouses: