Adding a hobby greenhouse to your garden

The winter seems to drag on and on this time of year for the avid gardeners in Southern Ontario who can hardly wait to get outside to work at one of their favorite hobbies. But don’t despair, there is a very pleasant way to extend our all too short growing season by starting your own plants in a cold frame or a hobby greenhouse near your house, protected from the last snowy gasps of winter.

If you have been spending loads of money on buying plants every spring, only to wish that they would live through the winter and come back next spring – now you can have an easy solution and save money while you are at it!

Whether you just use your greenhouse for a couple of months in the spring, or make it a four- season one, a hobby greenhouse not only provides the plants and flowers with the needed environment to survive the winter, but it can also give your hands and your mind the needed environment to ‘make it’ through the coldest of the fall and winter months.

You plant what you want, when you want and how you want. You control the sun, the lights, the water, the heat, and the cool air.

A hobby greenhouse is a place where you can grow whatever type of plant, flower or vegetable (and fruits!) that you desire. In the early spring months, you can start to sow your seeds, bulbs, all in hopes of having a great summer garden.

You can start and grow many unique varieties that you can’t find at local garden centers. And you can start them earlier to have larger plants to transplant in warm weather.

For instance, this gardener starts many flowers and vegetables indoors (even sweet corn and spinach) under lights starting in mid February. They’re moved to the greenhouse in late March, and depending on the fickle weather, transplanted to the garden from April to mid-May.

Most years we’re enjoying fresh vegetables by mid-June and even tasty ripe tomatoes by mid- July from a February sowing!

Although a hobby greenhouse can be used for growing plants year-round, increasing heating costs force many gardeners use them for only a few months in the spring and fall. However, every year new technology advances are giving us new coverings such as double wall plastics that reduce heating costs.

Getting started in a greenhouse is easier than you think. A structure can range from as simple as an old recycled storm windows to cover a cold frame, to a small hobby greenhouse costing a few hundred dollars to build, or even an elaborate greenhouse/sunroom addition to your house costing $50,000 or more. For this column, we’ll feature the very affordable hobby greenhouse.

The hobby greenhouse is usually constructed of a clear or semi clear substance that allows light in to the growing area so you can harness the power of the sun for your plants. If you like to grow plants that require little sunlight, you can use a shade cloth all of the time, and you can create shelving that makes shade in the greenhouse. No matter what climate you live in, you can expand your gardening hobby into the winter months with a greenhouse.

When this gardener caught the ”grow your own plants from seeds” bug four decades ago, the only small home greenhouses available had to come from England where everyone seems to have one in their back garden. But they cost thousands of dollars to bring here.

So, my first greenhouse 25 years ago was a self-built, 8-foot square structure. It was made from a kit of connectors from Lee Valley that fit recycled 2” X 2” lumber and was covered with 6 mil plastic vapor barrier. The floor was some old plywood sheeting on 4” X 4’s”. Originally built to last only one spring, that $100 investment has now survived 25 years and turned out thousands of plants for use around our home and “giveaways” to neighbours, relatives and friends (there’s a superstitious among many gardeners that giving plants away brings good luck to the gardener — works for me!)

By 2022, the hobby greenhouse industry has exploded in Canada, with dozens of companies offering a huge range of hobby greenhouse in all sizes and materials from $99 and up. Even the local hardware and Canadian Tire stores have reasonable priced small units available. Searching the Internet is another easy way to find them and a quick Google search the other day turned up 545 sites from Canada alone where you can get greenhouses and supplies. There is even a Facebook page now with over 21,000 members to ask for advice –

Hobby greenhouses are made of a variety of coverings and frames. Traditional greenhouses originally were covered with glass. However, glass is one of the least efficient materials to retain heat, so greenhouse glass should be double or even triple strength to increase heating efficiency and decrease breakage.

Fibreglass usually comes in corrugated form and is translucent rather than transparent. Fibreglass scatters light to create a virtually shadow less greenhouse. Fibreglass retains heat more efficiently while transmitting less heat into the greenhouse than glass.

UV treated polycarbonate provides much of the clarity of glass and is stronger and more resistant to impact than other glazings. It is also more fire resistant than other plastics. It comes in double walled sheets with many structural walls separating its two flat sides. It diffuses light to minimize shadows and has a 12+ year lifespan.

Polyethylene film now covers a large percentage of all greenhouse square footage in Canada. It’s popular with commercial growers because of its low cost and simplicity of maintenance. It lasts two to five years, depending on the thickness and UV treatment used, and then can be easily replaced with new poly film. Used in single thickness, it is good for simple cold frames and greenhouses used for starting seeds and other seasonal needs.

When used in two layers with the space between being inflated by a fan to create an insulated air space, polyethylene film retains heat more efficiently than glass. It is important to buy it from a greenhouse supply company to be assured of the UV coating.

Frames of traditional greenhouses were constructed of wood, usually redwood or cedar because of their natural resistance to the elements and glass. However, wood frames are larger and heavier than metal, thus increasing the shadow in the greenhouse and eventually wood will deteriorate in the humid climate of a greenhouse.

Galvanized steel is used in most commercial greenhouses because it is long lasting, inexpensive and strong enough to require less framework, creating less shadow in the greenhouse. It is usually covered in poly film.

Aluminum frames are usually used with glass or rigid coverings such as polycarbonate. It can be anodized in many colors and has low maintenance requirements. Not as strong as steel, an aluminum frame will have more members and create more shadow.

PVC pipe has become increasingly popular as a frame for greenhouses over the last five to ten years because of its extreme low cost, portability and ease of installation. Although not as strong as metal or wood frames, it can be strengthened with metal wire supports. Ideal for extending the growing season, starting seeds, growing transplants and winterizing plants and when covered with polyethylene film, it is the most economical type of greenhouse.

To grow year-round or in excessively cold or windy climates, however, a metal frame that could be fitted with an insulated covering would be a better choice.

Because of high winds and heavy snowloads in Ontario, it’s critical that the greenhouse be securing anchored to a heavy foundation and the frame be strong enough to withstand a couple of feet of wet snow.

Other features to consider:
• Lighting: Lighting your greenhouse benefits your plants and also allows you to garden after sundown.

  • Heating: Heating your greenhouse will allow you to grow all year round.
  • Ventilation: No matter what type of heating method you choose, you must keep the air circulating to prevent the heat from collecting at the top of the house. Heat retention is increased when the greenhouse flooring or foundation is rock, gravel, or concrete.

• Cooling: A must if growing in hot summer. Most plants are happiest in temperatures ranging from 60 to 75 degrees. A vent in the rear of the greenhouse with minimal dimensions of 36″ x 36″ is advised and fans are easy and convenient methods of cooling. Shade cloth with 65% to 85% shade capacity is a very inexpensive way of cooling a greenhouse.

• Watering: An irrigation mist system will help maintain moisture in the greenhouse, which is very important in prolonging plant life.

Knowing how you intend to use the greenhouse and establishing a budget will help you decide what kind of greenhouse you need and how many options and accessories to add. Because most gardeners tend to expand their gardening once they have a greenhouse (mine has grown to 8’ X 16’!), it is a good rule of thumb to get a greenhouse bigger than you think you need.

To help you decide whether you would like to get a hobby greenhouse, there are now many books published on the subject. Try your local library or bookstore. Here are some of my favourites: A beginner’s guide to using a hobby greenhouse

Roger Marshall: The greenhouse gardener’s manual

Green Div: Greenhouse growing for beginners

Andrew Mefferd: The greenhouse and hoophouse grower’s handbook

See you in the greenhouse!

Submitted by Jim Fitzgerald