Greenhouses and Cold Frames

This simple overview of sawtooth greenhouses and cold frames will give you a feeling of what to look for and how to plan your project and reap a heavy harvest.

Greenhouses,cold frames,and hot frames are all useful in extending the growing season and/or protecting new plants and seedlings.Which type of structure you select depends on the size and location of your growing area,how much money you have to spend,,and how much time you have to grow.Simple cold frames and hot frames can be assembled from common materials like old,framed windowpanes and hay bales.Greenhouses are generally larger and more complex.They can be expensive to build and maintain but offer more flexibility for growing time and building use.

When deciding on a growing structure,first carefully analyze the project on paper.Consider how much space you have for the footprint and how many plants you can grow safely.Cold frames are small and can be as simple as a glass or plastic frame set on the ground with on artificial heat source.Their basic function is to protect young plants and seedlings from wind and cold in the early spring,but they can also be blacked out to induce early flowering and harvest.Hot frames are similar in size and structure but provide heat through manure,electricity,steam,or a hot-water pipe (radiant heat).You may use a hot frame to raise early seedlings and cuttings,after which the structure can be converted into a cold frame.Both frames share the advantages of economy,simplicity,small size,and portability.

Both large and small greenhouses cost more money,time,and space.With the exception of the lightweight “hoop”house or miniature greenhouse,they are also more permanent.The type of greenhouse selected will be determined by its location and the panned use of the space.A learn-to or attached greenhouse will probably be smaller and less expensive to build than a freestanding structure.

Total area of the greenhouse is determined by the number of plants you intend to grow.Allow one square yard per mature plant.Do not forget to allow about six inches (15 cm) space for air circulation between benches and sidewalls.Add space for walkways-standing room only or room for a wheelbarrow-and possibly a center bench.Glass,plastic panels,and sheeting all come in standard widths,and it is easier to build in a size compatible with these units rather than have to cut the panels down.For example,an eight-foot (2.4 m) house can be made with two 48-inch (120 cm) wide fiberglass panels.Center height depends on the level of the eaves.Low growing plants can take an eave of five feet (1.5 m);tall plants need six or seven feet (1.8 or 2.1 m)..After determining eave height,a simple formula will give you the center height:Center height=eave+0.25 width.A twelve-foot wide (3.6 m) house with a five-foot (1.5 m) eave will have a center height of eight feet (2.4 m).

Budget and building sills will weigh heavily in the decision-making process.The last expensive structure per square foot is an even-span 16-foot wide that will house two side-beds or benches,that will house two side-beds or benches,two walks,and a wide center-bed or bench.An eight to twelve foot wide lean-to with wide beds or benches and a central walk is the least expensive option overall.Whichever option you choose,building it yourself will be cheaper than hiring a contractor.You can purchase many of the plumbing and electricity installations in kits or pre-assembled.

Climate will play a role in choosing your greenhouse.For example,a cold frame in the mild Pacific Northwest can give you a six-week jump on the growing seasons.This would not work in a colder region like the upper Midwest.Likewise,a hot or tropical area will require more shade and water.While the large cold frame is the most economical of structures,it will not function as a cold-climate garden.Location and exposure will depend on climate,but in general,you will want the greenhouse to be sheltered from strong winds and to be away from any areas where falling limbs or other debris might be a problem.There are a number of external design options.Cold frames can be as simple as a window sash laid over a rectangle of straw bales or a piece of plastic stretched over a metal or PVC pipe frame and held in place with clamps.Duct tape also works wonders to keep plastic in place.The advantage to plastic sheeting is that it can be removed during the day to take advantage of fresh air and the sun’s warmth and them be replaced at night to protect plants from cold air.The cold frame can be easily converted to a hot frame by installing electric heat and a watering/misting system.

Greenhouses can be attached (lean-to,window-mount,even-span) or freestanding.A lean-to uses an existing structure for one or more sides and is limited to single or double-row plant benches with a total width of seven to twelve feet (2.1-3.6 m) and length up to that of the building.The advantages of the lean-to are its proximity to electricity,water,an heat,but on the downside are its limited size,light,ventilation,and temperature control.

A window-mount replaces an existing window,providing a relatively low-cost way to grow short plants,small seedlings,or cuttings.It can be installed fairy simply with common household tools.The disadvantage if its small size.

Low-profile greenhouses are perfect for crops of short plants.It is easy to set up a low-profile hoop house of a greenhouse alongside a building that gets full sun.The short greenhouse or cold frame is simple to darken during full summer and lets you reap the benefits of the harvest early!

Small greenhouses and cold frames also work well on patios,balconies,and roof-tops.They protect plants from wind.

An even-span can be an attractive option.Like the window-mount o lean-to,the even-span is attached to the house and bears similar limitations of size,light,ventilation,and temperature.Unlike the lean-to or window-mount,the even-span can be larger an can open into the house-providing heat and humidity-or even function as a conservatory,an attractive place to relax.It is,however,more expensive to heat and maintain.Such greenhouses are most popular.

The freestanding greenhouse offers the most flexibility in size and location.It can be built to take full advantage of the sun,but it does not retain heat well and can be expensive to keep warm.Many frame types and coverings are available in kits or raw materials.

Mobile Vertical Farming can be in wood or metal.You may select a panel frame which is more expensive to build (panels are individual units) but has the advantage of quick installation and breakdown for storage.If portability is an issue,there are miniature greenhouses and hoop houses that can be purchased as a kit for under $300.These structures,because they can be picked up and moved,are usually considered temporary by municipalities and often do not require permits.