2009-03-05 / News

Gardening 101: Greenhouse smarts

The Island Garden
By Roger Marshall

Growing plants in a greenhouse is a little more advanced gardening than growing outdoors, but the basic principle is the same. In a greenhouse you won't be able to rely on rain to water your plants. You also won't be able to rely on insects to pollinate your plants. You will have to water and pollinate your plants. But other than that, most greenhouse gardening is the same as outdoors.

It can also be much more than outdoors. Growing in a greenhouse moves your gardening zone up one zone at least. In Jamestown we grow in zone 6b according to the USDA plant hardiness zone. This map tells you when the first and last frost dates are expected for your area, what plants will survive in the area and a lot more. The zones are rated from the lowest (in northern Canada) to the highest in southern Florida. In Jamestown, we can grow any plant that is rated lower than zone 6b. In an unheated greenhouse, we could grow plants that are rated for zone 7b. If you heat your greenhouse you can grow plants that are rated up to zone 10. For example, in my heated greenhouse, I grow lemon, orange and key lime trees that are normally found in places like Florida.

If you want to buy a greenhouse there are many things to look out for. So many, in fact, that I have written a book about it. You can buy a copy at Jamestown Hardware if you want to look into greenhouse gardening more deeply. Here are a few things to look for:

If you can afford it, buy doublewall acrylic glazing rather than single wall glazing. It will last longer and insulate better.

Buy a wooden-framed greenhouse rather than an aluminum framed greenhouse. Buy the largest greenhouse you can afford. You will fill it with plants if you are a keen gardener, and you will wish you'd bought a larger one. If you are a beginning gardener, buy a smaller greenhouse until you learn how to use it.

If you plan to heat it, buy double or triple walled acrylic glazing. It is lighter than glass and has a high insulation value. If you plan to heat it put the greenhouse on the south side of a building to help keep the northerly wind off it.

Put your greenhouse near a water supply and an electrical outlet. Watering the plants is the biggest single chore to greenhouse ownership. In summer you can move your plants outdoors and water them daily with a hose, but in winter you'll need to water at least once a week. If you enjoy greenhouse gardening, you'll want to be able to go out there at night after work, so having lights out there can make it fun. Plus, you can plug in a heater or water pump if needed.

You can make your greenhouse freestanding or make it a lean-to against your home. Each has advantages and disadvantages.

The advantages of a lean-to greenhouse

Solar heat can be used to heat your home in winter if you have a door into your greenhouse from the home. This warm air is usually quite moist but it may smell a little earthy.

Power and water are easy to supply. Heat can also come from the home. But it can draw heat from the home on cold overcast days.

You can work out there at night without trudging through the snow.

It can serve as an adjunct to your home and give you a warm place to sit on a cold sunny day.

You can easily move flowering plants in bloom into the house for all to enjoy.

You can easily pick herbs and other food plants without going outside.

The advantages of a freestanding greenhouse

You can spray chemicals without the smell getting into your home.

You keep greenhouse debris (pots, potting soil, etc.) out of your home.

It can be located where it will get the best sunlight and near the garden to make moving plants into the garden easier.

A greenhouse can be fun, but it can also be a chore. It helps to increase your gardening season to almost any length you want, including year round. With a greenhouse you can grow exotic fruits, vegetables, and herbs that you might not be able to find in a store. For example, I grow galangal for Thai cooking in the heated greenhouse. This is a plant that is normally only available by mail order.

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