Gardening with Greenhouses - Solitude Springs Farm & Vineyard

Gardening with Greenhouses Aaron Stierle Solitude Springs Farm & Vineyard Spring 2013

Greenhouses and Concept • Transparent to translucent structures constructed to trap heat and moisture • “Greenhouse effect” - where the short wavelengths of visible light from the sun pass through a transparent medium and are absorbed, but the longer wavelengths of the infrared reradiation from the heated objects are unable to pass through that medium • A major part of the efficiency of the heating of an actual greenhouse is the trapping of the air so that the energy is not lost through convection

Greenhouse Effect

Benefits • • • • • •

Longer growing season Warmer temperatures for heat-loving plants Earlier harvests Can grow greater variety of plants Reduced water consumption Reduced (in some cases) pesticide use

Disadvantages • • • •

Can overheat – require ventilation Excessive moisture can lead to fungal diseases Require water during rainy season Require annual and seasonal maintenance – Annual maintenance: repair/replace transparent cover, structural preservative treatment, cleaning – Seasonal maintenance: winter snow removal, dust removal during dry season, etc.

• Voles can be a problem

Construction Ideas • Many options are available – Frame: wood, metal, PVC pipe – Shape: Gothic, peak roof, lean-to, high tunnel, low tunnel – Glazing: glass, rigid plastic panels, clear plastic sheeting (Visqueen). – Size: small (6’ x8’) to large (48’ x 96’)

Examples

Fig 1. Gothic, polycarbonate

Fig 4. Hoop house/high tunnel

Fig. 2 Peak, Visqueen, wood

Fig 5. Glass, wood

Fig. 3 Glass, metal

Fig 6. Lean-to, wood, polyc.

Foundation • Permanent structures benefit from a foundation • Simple hoop houses (low tunnels) use 2’ or 3’ rebar pounded into the ground and pressuretreated wood to help hold the rebar in place • Anchored cinderblock walls can also serve as a foundation, but frost heaving on permafrost can disrupt them.

Foundation/Floor • “Floating” concrete pad – concrete pad poured on gravel bed • Typar/geotextile floor – use durable plastic fabric tacked down with ground staples to prevent weeds and form a floor to walk on, self-draining • Elevated wood floor – use pressure-treated plywood over floor joists and posts • Provide for drainage!

Framing • Wood: – Use pressure-treated wood to prevent rot from moisture condensation. Do NOT use CCA treated wood (not marketed since 2003) – Readily available and easy to cut into shapes – Relatively lightweight, but expensive – Use appropriate dimensions to support snowload, can intercept a significant portion of sunlight

Framing • Metal: – Strong and durable – Needs proper treatment and maintenance to prevent rust if aluminum is not used – Can use old military-style double-hung aluminum windows as walls of greenhouse – Use caution if covering metal frames with plastic sheeting to prevent tears or snags

Framing • Plastic – PVC pipe is readily available, relatively strong, rot resistant, and easy to work with – Typical cross-section is a half circle – Maximum size is limited by strength of PVC pipe – May require removal of the cover during the winter. – End wall construction can be complicated – Can break during very cold weather if hit

Shape • Gothic arch: – Sheds snow, maximizes height – Can be difficult to build end walls – Requires bending glazing panels

• Peak roof: – Sheds snow if roof pitch is 45 degrees – Best if supported under peak, reduces accessibility

• Lean-to: – Attached to a structure

Shape • High tunnel: – – – –

Rounded top (with or without sidewalls) Greater vertical space available Prone to damage from wind and/or snow; UAF Most successful in snowy/windy climates if cover removed during winter – Maintenance and ventilation can be difficult due to excessive height (often 12 ft high or greater) and sheer volume of interior – Costly to buy, ship, and erect; winter removal – Popular with growers of specialty crops

Shape • High tunnel (con’t): – Some have elaborate mechanisms to roll up sidewalls to assist with ventilation – Hoop houses are low-cost version that use PVC pipe and polyethylene plastic sheeting • maximum height only in center and decreases rapidly toward edges • Moderately resistant to wind damage during growing season; hail/heavy rain can be a problem

Shape • Low tunnel: – Cheapest, easiest to install; occasional cover replacement – Mini hoop-house design – half circle arch; maximum height only in center and decreases rapidly toward edges – Resistant to wind damage during growing season; hail/heavy rain can be a problem – Usually 3-4 ft high and wide; no end walls or modifications for ventilation – Cover a single row or a raised bed

Glazing • Glass: – Long-lasting and no need to replace unless broken – Durable, unaffected by mold or mildew – Can have very high light transmission rates – Very expensive, unless using old windows

Glazing • Plastic greenhouse panels (polycarbonate) – Moderately long-lasting; contain UV inhibitors – Precut to standard sizes – Replacement is usually not difficult – Expensive ($1.40/ sq. ft), but typically more durable than glass – Double layer “corrugated” designs add insulating quality – Vary in amount of light transmitted

Glazing • Visqueen (clear polyethylene plastic sheeting) – Relatively cheap (5¢/sq. ft.), readily available in a variety of sizes and thicknesses – Lightweight and easy to work with – Varies in light transmissivity, but generally lower than glass and polycarbonates – Least durable, lowest insulating value, tends to billow in wind – Rapidly degrades (