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How to start a greenhouse

Practical advice on getting a greenhouse going in your backyard

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More than a place to grow seedlings, a backyard greenhouse can be a sunny retreat on chilly fall days. Learn how to set one up on your property.

Home greenhouses have come a long way in the last decade. They are no longer ramshackle constructions of leftover windows, plastic sheeting and rickety wooden frames. Though these basic options can still work to shelter spring seedlings, pre-made greenhouses are becoming popular among gardeners looking to create a unique focal point in the garden.

Greenhouses can hold exotic fronds and flowers, setting the mood for a garden cocktail party in August. They can become a warm, sunny meeting room that inspires summer ideas in January. They can even revive you in March when you just can’t stand another moment of winter. Plus, they will still start those seedlings in spring and prolong your harvest in fall.

You can buy pre-made greenhouse kits in stores or online. Or if you want a classic “glass house” or “conservatory” from the world’s garden capital—England—that’s available, too, complete with roof ridge cresting and finials. Prices range from $100 for a walk-in and functional 1.8-by 2.4-metre space surrounded by plastic, to $1,500 and more for a glass-enclosed beauty with automatic heating and cooling.

When deciding on a greenhouse design, your first consideration is location. Picking the best spot is a balance of five requirements: maximum sunlight, access to electricity and water, good drainage, protection from prevailing winds and general convenience.

At $59.99, Canadian Tire’s soft-sided PVC model is an affordable greenhouse option.

At $59.99, Canadian Tire’s soft-sided PVC model is an affordable greenhouse option.

Considering that you can get started with a small greenhouse for less than $60 [Canadian Tire has a PVC soft-sided greenhouse kit for $59.99], and less than $1,000 for a 1.8-by 3-metre one with clear-as-glass polycarbonate panels [Canada Greenhouses has one for $879], the real question is not whether you can afford one, but rather how soon can you get yours started —Larry Hodgson, author of over 20 garden books, including The Garden Lover’s Guide to Canada (2001, Princeton Architectural Press)

the real question is not whether you can afford one, but rather how soon can you get yours started.

—Larry Hodgson, author of over 20 garden books, including The Garden Lover’s Guide to Canada (2001, Princeton Architectural Press)

Setting your greenhouse with the ends facing north and south will give the sides full sun exposure. Try to anticipate how much shade surrounding trees or buildings will cast, both at the height of summer and during spring and fall when the sun is lower in the sky. Deciduous trees can be helpful as they shade summer heat when it’s hottest and allow the sun to slip in during winter when the branches are bare.

You will need access to electricity to heat and cool your greenhouse and to provide light. An electric fan can circulate the air to cool and give a healthy atmosphere for the plants. Easy access to water is important for both the plants and the gardener, particularly if you are planning for underground pipes.

Commercial gardeners say that the person who waters the plants determines the profits. Watering is just that important. You can lose a greenhouse full of plants in one hot day if you do not water them properly.

Select a well-drained location. Whether your floor is concrete or earth covered in gravel, you don’t want water pooling in or around the greenhouse, creating a muddy mess or a frozen accident waiting to happen.

Prevailing winds can add cost to your heating in late fall, winter and early spring. An ideal location would have an open fence or planting about 4.5 metres away from the greenhouse to help break up the wind. A solid fence or planting at the same distance actually speeds up the wind, forcing it over the top and resulting in colder air. Make sure the walls, windows and door are airtight to contain as much warmth as possible.

Another way to save heating costs is to lower the overall temperature. Many plants will thrive in temperatures two or three degrees below optimum and this can make a significant difference in your total heating costs.

Consider the overall convenience of your greenhouse location, too. While the ideal site may be in the far corner of your property, you may never bother to go there. Try to locate it somewhere that will become a natural part of your garden stroll.

Also look at the interior of your greenhouse. For seedlings, flowers and vegetables, include as many sun-splashed shelves as possible. Plants that flourish in the shade can sit on the floor under the shelves. Be sure to save space on your shelves, usually near the door, for a potting area. Keep a large container underneath to collect the excess soil you will spill.

Ventilation is necessary and most pre-made kits include some type of vent. Not only is it important to help regulate the heat, it’s also necessary for the health of the plants. Locate the vents at the highest point of the greenhouse and at bench height on the sides. The larger the greenhouse, the more vents you need.

Sanitation is an oft-neglected requirement. It’s easy to control pests and disease if they never gain a foothold. Remove dead or diseased plants, clean up decaying foliage and check all new plants for problems before bringing them into the greenhouse. You can also clean the inside of your greenhouse with a solution of 1/4 cup (60 ml) of bleach to one gallon (3.7 litres) of water and wipe down all surfaces at least once a year.

Maintaining a greenhouse isn’t for everyone. But for gardeners with the time and interest, starting perennials from seed can save hundreds of dollars. There are so many other reasons to have a greenhouse in your garden—from entertaining a crowd to having a quiet cup of coffee in a sunny spot in the middle of winter. Consider it a mental-health priority.

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