Editing Season extension (section)

==Structures==

* Unheated [[greenhouse]]s (also known as ''cold houses'') offer protection from the weather, such as sub-optimal temperatures, freezing or drying winds, damaging wind gusts, frost, snow and ice. Unheated greenhouses can extend the growing season of [[cold hardy]] vegetables well into the fall and sometimes even through winter until spring. Sometimes supplementary heating is appropriate when temperatures ''inside'' the greenhouse drop below 32 degrees Fahrenheit.<ref name="Coleman-2009""/>{{rp|pages=2-12}}

* Passive heated or low-energy greenhouses: Using principles of [[passive solar building design]] and including [[thermal mass]] will help keep  an otherwise unheated greenhouse several degrees warmer at night and on [[overcast]] days.<ref>[https://www.cochranetoday.ca/opinion/passive-solar-greenhouse-is-an-elegant-solution-to-extend-your-growing-season-2714492 Passive solar greenhouse is an elegant solution to extend your growing season], CochraneTODAY.ca, September 18, 2020</ref><ref>[https://www.gardenandgreenhouse.net/articles/november-december-2011/passive-solar-heating-for-greenhouse-operations/ Passive Solar Heating for Greenhouse Operations], Garden & Greenhouse, September 5, 2011</ref><ref>[https://atmosgreenhouse.com/blog/the-case-for-a-mostly-passive-solar-greenhouse The Case for a (Mostly) Passive Solar Greenhouse], Atmos Greenhouse Systems</ref> Other systems such as [[ground-coupled heat exchanger]]s, [[solar chimney|thermal chimney]]s, [[thermosiphon]]s, or "climate batteries" can also be used to take ground-stored heat and use it to help heat a greenhouse.<ref>[https://ag.umass.edu/greenhouse-floriculture/fact-sheets/geothermal-heat-for-greenhouses Geothermal Heat for Greenhouses], University of Massachusetts Amherst, 2008</ref><ref>[https://atmosgreenhouse.com/blog/sources-of-free-heat-in-a-climate-battery-greenhouse Sources of Free Heat in a Climate Battery Greenhouse], Atmos Greenhouse Systems</ref>

* [[Polytunnel]]s (hoop houses): Whereas a greenhouse has a frame and is glazed with glass or stiff polycarbonate sheets, polytunnels are built with thin polyethylene plastic sheeting stretched over curved frameworks, often extending as long "tunnels". ''Low tunnels'' are short enough that a person cannot walk inside them, perhaps 2 to 4 feet tall, and the plastic must be lifted to access the plants. ''High tunnels'' are commercial-sized buildings, tall enough to walk through without bending and sometimes tall enough to operate tractors inside. Sometimes polytunnels are built with two layers of plastic sheeting and air blown in between them; this increases the insulation factor, but also cuts down on the amount of sunlight reaching the plants.<ref name="Coleman-2009""/>{{rp|pages=55-58, 125-130}}

* [[Row cover]]s are lightweight fabrics placed over plants to retain heat and can provide several degrees of frost protection. Row covers, being fabric, allow rain to permeate the material, and also allow plants to [[Transpiration|transpire]] without holding in the moisture (as happens under plastic sheeting). Row cover material can be laid directly onto the crop (''floating row covers''), or laid over a framework of hoops or wires. Row covers can be set up outside of any protective structure or placed over crops within high tunnels or greenhouses. In its simplest function, it allows a light frost to form on the cover instead of on the leaves beneath. Outside row covers must be clipped or pinned in place or weighted down on the edges. Inside row covers may be draped to the ground without further attachment.<ref name="Coleman-2009""/>{{rp|pages=58-66}}<ref>{{Cite web|title=Row Cover & Insect Netting Options & Uses {{!}} Comparison Chart (PDF)|url=https://www.johnnyseeds.com/growers-library/tools-supplies/row-covers-comparison-chart.html|access-date=2020-11-06|website=www.johnnyseeds.com}}</ref>

* [[Cold frame]]s are transparent-roofed enclosures, built low to the ground, used to protect plants from cold weather. Cold frames are found in home gardens and in vegetable farming. They are most often used for growing seedlings that are later transplanted into open ground. A typical cold frame has traditionally been a rectangle of framing lumber with an old window placed over it. Since the advent of plastic sheeting, it is often used instead of old windows. 

* Temporary coverings: In smaller gardens almost any type of cover, including [[Cloche (agriculture)|glass cloches]], newspaper cones, baskets, miscellaneous bits of plastic, and mulches such as hay, leaves, or straw can be used as frost-protection that is pulled on and off each day when frost is likely to occur overnight.