It sounds simple. You want to grow for an extended season, or perhaps year-round. Cultivating small fruit under cover may be intriguing, or perhaps hydroponics sounds appealing, and a controlled environment is a must. A protective growing structure – a cold frame, high tunnel, or greenhouse – is needed. Choosing the correct structure, however, can be complex.

The frame type, height, width, door openings, coverings, ventilation, heating and other options must be carefully chosen, according to desired use. You also need to consider initial cost, cost of operation and future plans for expansion. Some structures excel at being not only year-round growing houses, but also retail showrooms. Others are bare-bones options, such as a cold frame, designed as an entryway into extended-season growing at a minimal cost.

Donabedian Bros., Salem, N.H. Finding the correct system for your specific circumstances starts with understanding the needs of your intended crops.

Planning for growth

“Keep things simple but efficient in the planning process,” Bob Rimol, the founder and owner of Rimol Greenhouse Systems (RGS,, advised. “You can always do add-ons later to become more automated and self-sufficient.”

Perhaps the most important logistical question to ask is: “Where is the best site location for my greenhouse?” Improperly sited greenhouses lead to drainage issues, collapse from snow or wind, a detrimental growing environment with poor sunlight or airflow, and ultimately to failed crops.

Freestanding greenhouses shouldn’t be located too close to other structures. Snow accumulation, drainage and wind received by the greenhouse are impacted by nearby structures or trees. Shade is also a concern, and the shadow of large, nearby trees or buildings can block sunlight. Situating the greenhouse to optimize sun exposure, particularly the important morning sun, is recommended. The seasonal changes in sun angle must also be factored in, as winter and summer sun will differ. You should also consider what crops will be grown and whether the greenhouse will see year-round or seasonal use. Simply orienting the greenhouse for best sun exposure, on an open site with good drainage, can go a long way toward providing the best environment for a healthy crop.

Terraced ground is prone to drainage issues and should be avoided, while rocky ground is usually workable with some extra effort. Stormwater runoff issues should be addressed as well, and any setbacks from wetlands or water bodies taken into consideration. Local ordinances regarding greenhouse structures should be reviewed to see if any site plans or permit approvals are needed. And if you are planning more than one greenhouse, it is prudent to allow at least 12 feet between them, both for snow removal and taking off the covering.

Determining the size of the needed growing area is a critical step. Too much space means added costs for any supplemental heating, as well as a large investment for a small return. While getting caught short on space can be remedied in the long run, it will cause immediate frustration.

“The main issue is planning your growing with a layout of the crops, and adding 20 percent extra space as a contingency,” Rimol said.

Greenhouse types

Do you need a basic system, with an arched frame, roll-up sides and removable coverings, or are your needs more complex? Basic extended-season growing space – whether planting crops in the ground, or in trays on benches – can be had with a cold frame.

RGS’ cold frame model, the Catamount, is 15 feet wide and comes in lengths of 48, 72 or 96 feet. The model is given extra strength via a cross-connected purlin, allowing it to withstand some snow accumulation. The bows can be placed 4 or 5 feet apart, depending on growing needs. Due to its size, the Catamount works well for standard 15-foot ground coverings, as well as standard 24-foot widths of polyethylene covering. Options include roll-up sides (automatic or manual), a heating system, extended ground posts for added height, and manual or automated ventilation.

American Horticultural Supply offers Quonset and grid-style cold frames. Standard and oversized Juwel cold frames are available from A.M. Leonard. GGS Structures’ cold frames are constructed with high-quality steel arches for protection from rust and corrosion. International Greenhouse Co. and Atlas Mfg. also offer a variety of cold frames.

If more sophisticated options are needed, a variety of greenhouse frames are available from RGS in 18 to 34-foot widths. The basic Eastpoint model is a suitable option for growers looking to overwinter vegetable crops. Gas heating options, mechanical ventilation and automated side roll-up options add convenience, while the optional polycarbonate end walls add durability. It features a stronger Gothic-style frame, designed for added wind and snow loads.

“The Eastpoint is much stronger, so there is no worry about snow load,” Rimol said. “Eastpoint is much more open and airy, so you do not get the heat buildup like you would with a cold frame. There are more options available with an Eastpoint.”

Agra Tech’s commercial greenhouses are designed to optimize natural ventilation. Freestanding and gutter-connect models are available from Atlas Mfg. Nexus Greenhouse Systems offers Quonset, Gothic, peak, curved, straight and open roof designs with a variety of coverings. Ludy Greenhouse Mfg. Corp. and Stuppy also offer a wide variety of greenhouse models. Advancing Alternatives supplies roll-up curtain systems, including freestanding, gutter-connect and curtain wall types, as well as controllers and other equipment.

Moving up

While there is no formal, standard definition of a high tunnel, many define a high tunnel as a nonpermanent structure with no permanent heating system, designed for basic extended season use. RGS considers a high tunnel to be any greenhouse structure that has elevated sidewall heights to allow equipment to pass through. At RGS, high tunnel structures come in all shapes and sizes, from simple structures providing a few weeks of extra growing time, to full-year growing houses, complete with complex heating and ventilation. The height of most RGS greenhouse models can be adjusted upward, making the greenhouses into a “high tunnel system,” by using extended-length ground posts.

More complex greenhouse styles come in a variety of widths, and even with varying sidewall heights. Do you need standing access throughout the width, or are low-sloping sides workable? Do you require something more permanent than polyethylene coverings, which need to be replaced after several years? Some models have ridge vent options, a choice of gas or oil heating options, additional mechanical ventilation options and more.

Door options (single or double, sliding, hinged, or roll-up) allow for ease of access and can also make the structure more attractive for retail space. Doors can be constructed from several materials, and insulated doors may be warranted, depending on use.

Rimol advises growers not to overreach, but to be realistic about how they are going to use their structure, the time they will devote to managing the greenhouse environment, and the needs of the crops they are growing in the greenhouse. While growers should be realistic regarding their goals, cutting corners will add to the time it takes to manage the greenhouse, Rimol cautions.

Monkshood Nursery, Stuyvesant, N.Y. Freestanding greenhouses shouldn’t be located too close to other structures.

“A few conveniences like motorized roll-up sides or motorized gable shutters will allow you to not ‘babysit’ the greenhouse and protect you against fluctuations for heating or cooling,” Rimol said. “Although polycarbonate ends are more expensive, they are a better investment for the long term. You have triple-wall polycarbonate, which is a much better insulator than single-layer poly. The other advantage is that the polycarbonate on the end walls will last about 20 years, so there is no maintenance, versus changing the poly every four or five years.”

Ventilation is another serious matter to be considered. It helps to control humidity levels, which are critical in greenhouse crop production, as well as the carbon dioxide exchange rate. CO2 is a crucial component of plant photosynthesis and growth, and proper airflow reduces disease pressure. The necessary airflow exchange rate is calculated based on the structure’s area in cubic feet. The rate can be achieved passively without fans, by rolling up sides and opening any ridge or wall vents, either manually or with an automated system. Mechanical ventilation options include automatic fans and motorized shutters and can be operated by state-of-the-art computerized environmental control systems.

While glass has been the traditional greenhouse covering, and fiberglass has faded out of style, most structures today are covered with either polyethylene, in single or multiple layers, or polycarbonate, which can also be in single or multiple-layer construction. Light penetration, heat retention and the expected life of the covering are some factors to consider, along with the initial and replacement costs. Inflation blowers can be used between polyethylene covering layers to enhance insulating ability.

Donabedian Bros., Salem, N.H. Be realistic about how you are going to use your structure, the time you will devote to managing the greenhouse environment, and the needs of the crops you are growing in the greenhouse.

Not every grower needs the most exclusive options, but depending on your business plan, a greater initial investment might make sense. Beginning with a higher-end frame, in a smaller size with fewer options chosen, and adding size and options as the business expands might ultimately be a better economic decision, compared to beginning with a basic structure when a more controllable environment is warranted. Someone looking to grow an array of hydroponic greens year-round, for example, might want to consider a more advanced system from the start.

Monkshood Nursery, Stuyvesant, N.Y. Structural options, site selection, initial cost and plans for future expansion are all things that should be considered when choosing a greenhouse.

Specialized equipment

RGS offers four levels of hydroponic greenhouse packages. Hydroponic systems begin on the Northpoint or Nor’Easter greenhouse frame. The Nor’Easter model is meant to withstand adverse weather conditions, with a truss support system designed to double the strength of the bows.

The hydroponic packages feature 8-millimeter triple-wall polycarbonate, a double layer of 6-millimeter polyethylene film, locking insulated doors, exhaust fans and full ventilation system, plus heating options. More deluxe options include added fans, energy-saving film, environmental controller, insect screening, and longer or wider greenhouse frames.

CropKing offers hydroponic greenhouse systems for lettuce, herbs, tomatoes and microgreens.

Marett Farms, Londonderry, N.H. The Gothicstyle frame is designed for added wind and snow loads.

Another specialty greenhouse is the movable, rolling system. RGS’ Rolling Thunder model has tracks two times its length and a wheel system. The rolling system allows a grower to maximize use of the greenhouse by starting one crop, then relocating the house over new ground for a second greenhouse crop, to provide protection to tender crops at the end of the season, or to allow crop rotation, cover cropping and other techniques to be implemented without sacrificing the ongoing use of the greenhouse.

Four Season Tools and FarmTek also offer movable structures.

Do your homework

“Rimol Greenhouse Systems works closely with growers of all abilities. Many of the purchasers are novices with little or no growing experience,” Rimol said. “RGS educates as much as possible about choosing the right structure with the correct options.”

Growers seeking to extend their season or embark on year-round growing operations need to do their research prior to making any greenhouse decisions. Finding the correct system for your specific circumstances starts with understanding the needs of your intended crops. Extending the season for tomato growing will require different specifications than growing cold-season vegetables under cover. According to Rimol, the deciding factors in choosing a system are “what you are growing, when you are growing, and how you are growing.”

The author is a freelance contributor based in New Jersey. Comment or question? Visit and join in the discussions.