Greenhouses can help overwinter tender plants, grow food all year, or just extend the growing season by several weeks to a few months. You can buy them ready-made, but it is cheaper to build your own with readily available materials – and it’s much easier building one when it’s warm.
Here are a few ideas for cheap greenhouses that can be put together in a day or two:
1. Simple pallet greenhouse
The simplest and most inexpensive greenhouse  can be made with a few old pallets. It may not accommodate a whole lot of plants, but can offer a warm home to a few precious ones over the winter. It can also be used to start your seedlings well in advance, too.
One pallet is used to make the floor and can keep pots well off of the cold ground. A square or rectangular frame made of pallet slats becomes the back. Two long slats can connect the back top end and the bottom front end diagonally to form triangular sides that provide structural strength.
A triangle fixed with clear plastic can be fitted on hinges to one of the sides. This forms the door of the greenhouse. Stapling clear plastic to the front and the other side completes the structure.
2. Mini greenhouse from recycled windows
You can have a small greenhouse to overwinter your ornamentals or house your herb garden with as little as three large glazed windows. The wall of the house or a garden shed serves as the fourth side of this square-shaped structure. With the eaves offering some protection against direct rain and snowfall, sheet glass or Plexiglas cut to the right size can serve as the roof.
You can use a pallet for the base and have a frame made of long wooden planks for attaching the three windows. One of them should be fixed on hinges to act as a door. The solid wall can be painted white for better light reflection or black for increased heat absorption. Provide shelves against this wall to maximize space utilization in this mini greenhouse.
3. Lean-to greenhouse
A lean-to greenhouse is a simple, yet sturdy structure owing to the supporting wall behind. It can be built against the wall of the house, garage or garden shed. Correct siting is very important in this type of greenhouses to take maximum advantage of sun exposure during the winter months. South-facing walls are traditionally preferred, but the amount of light received can also depend on the position of other buildings and tall trees nearby.
The slant of the lean-to is determined not only by the roof structure of the supporting building, but by the climate of the area. A steep roof is ideal for places experiencing heavy snowfall to avoid a heavy collection on the roof. The structural framework can be made of wood with framed panels of glass or Plexiglas fixed to them to serve as the sides. Corrugated plastic roofing is ideal for roofing as well as a door on hinges.
4. Freestanding greenhouse from old windows and glass doors
If you have some woodworking experience and a number of glazed windows and doors to recycle, a free-standing greenhouse of desirable height can be fabricated. The sides and the roof are all made of these windows fixed onto a wooden structural frame. Stacking the windows vertically will give plenty of space for tall plants and climbers.
Plants can be grown right in the ground or on raised beds or pots depending on the use. With a few louvered window panels incorporated into the design, the greenhouse will have much-needed ventilation during the hot season. That way, it can be a permanent structure in the garden to grow food year-round.
5. Cold frame greenhouse
Cold frames are commonly used as seedling nurseries prior to planting them out in the open, but these structures can do double duty as greenhouses, too. They are essentially wooden boxes with glass tops that can be raised to access the interiors and for ventilation. The back of the box is typically higher than the front so that the glass top lies at a slant to allow in more sunlight. Usually kept facing the south for longer exposure to sunlight, the tender seedlings get a head start in the warm microclimate inside these boxes.
If you already have a cold frame, you can raise it on a base made of bricks or concrete blocks to accommodate large plants and pots. Or you can convert tall cedar planting boxes into cold frame greenhouses. It involves increasing the height on one side by adding an extra panel and attaching glass panels or old windows on hinges to that side. Or you can make sliding doors with Plexiglas with or without a frame.
6. Soda bottle greenhouse
If you have plenty of soda bottles and lots of patience, you can make a greenhouse of any dimension. The structure needs a basic wooden frame, but the sides as well as the roof are made out of these transparent plastic bottles. The arrangement is modular with long panels made up of a number of bottles threaded onto sticks of a specific length. The bottoms of the bottles are cut and stacked tightly together on each stick.
After making plenty of these modules, they can be arranged close together and then nailed to the wooden frame to form the sides and the roof. The sunlight passing through the glass bottles keeps the air inside the greenhouse warm, but the structure is otherwise open to the elements as there are plenty of air gaps in the roof and the side walls. If you need more insulation, you can cover the structure with a sheet of clear plastic or bubble wrap.
7. Portable mini greenhouse
A plastic-covered lightweight greenhouse is a great option if you have plants growing in heavy pots. Instead of bringing the pots into the greenhouse, you can take the greenhouse to where the pots are kept. This greenhouse is made with half-inch PVC pipes interconnected to form a Quonset-type structure.
Materials such as PVC pipes, 3-way elbow connectors and adapters can be sourced from a plumbing supply store. Scissors and a hacksaw are all the tools you need to cut the materials and assemble the structure, but primer and PVC cement can be used to make the joints strong and stable. After making the structural frame with the pipes, it is covered with clear plastic sheeting. The plastic is fixed to the frame with zip ties.
Clear plastic sheeting is inexpensive and usually lasts only a season, but the frame can be reused with fresh plastic covering. Visqueen is a bit more expensive, but more durable.
8. Barn-style greenhouse
If you want to build a sturdy, permanent greenhouse, you should go for the barn-style structure that can withstand the vagaries of nature. It will give you great returns for your time and effort, and can be used year-round for growing food.
It basically has a typical barn-style wooden framework that is then covered by transparent polycarbonate sheeting for the roof as well as the sides. Corrugated plastic sheet that combines strength and excellent flexibility can be used, too.
The roof can be gambrel, gabled, or slanting one-way (skillion), depending on how much rain and snow your area receives. The plastic sheets are fixed to the wooden frame with screws. These sheets can be easily cut into size with a circular saw, but keep the dimensions of the barn the same as the standard sheet length to reduce labor and wastage.
What DIY greenhouse ideas have you tried? Share your suggestions in the section below: