Why do you want a greenhouse?
What sort of greenhouse is right for you?
Gardening in a greenhouse Resources

Why do you want a greenhouse?
Most gardeners would love to own a greenhouse. This appeal may be strongest in cold climates, but being able to grow an endless supply of sturdy little seedlings is a pretty appealing concept no matter where you live. And what gardener isn't intrigued by the idea of having a tropical environment filled with orchids, citrus and jasmine; or wouldn't relish the opportunity to pick fresh salad greens and vine-ripened tomatoes on a cold winter day. There are now dozens of affordable, well-constructed greenhouses on the market, as well as a full range of accessories that make greenhouse gardening easier than ever.

This may seem like a simplistic question, but function is really the most important factor in determining the type and size of greenhouse you choose.

An attached greenhouse or sunroom is the right choice if you want a place to read and putter among potted plants. For starting seeds, a freestanding polyethylene-covered hoop house can probably give you everything you're looking for. If your objective is to have a nearly year-round supply of fresh greens and herbs, you may want to consider a solar greenhouse that requires little or no supplemental heat.

Can you imagine yourself tending an extensive collection of orchids, propagating begonias and experimenting with oleander and passiflora? If so, you'll want a well-insulated, professional-quality greenhouse that can be temperature-controlled year-round, with running water, a power source for supplemental lights, active ventilation and plenty of room for expansion.

Appearance may also be an important consideration. Will you be happy with a polyethylene hoop house, or is it important that your greenhouse be a more aesthetically pleasing addition to your home and your landscape?

Climate and location are crucial considerations. One reason greenhouses are so popular in England is that their climate is far more moderate than what most of us must cope with here in the U.S. Operating a year-round greenhouse in Vermont or Minnesota usually requires an insulated foundation, double glazing, insulating shades, buried power and water lines, and a serious financial commitment for heating.

In the summer, maintaining a plant-friendly environment may require shade cloth, multiple fans and a misting system. But people who do have a greenhouse, and have tasted the pleasures of being able to fuss around in their own warm, plant-filled jungle, would be quick to argue that the benefits outweigh the challenges.

What sort of greenhouse is right for you?
Custom Design or Kit?
There are now so many companies offering so many different styles and price ranges of greenhouses, that there's little reason to start from scratch designing your own. The exception to this is if you are building a new house, or are concerned about integrating your greenhouse into the architecture of your home. In this case, it may be wise to seek some professional advice.

Greenhouse kits may be as elaborate as a site-built gazebo room with turrets, or as simple as a box of plans with some hardware and a roll of polyethylene. Send for literature on all the greenhouse kits that interest you. Get on the Internet. Ask other gardeners about their experiences. And be sure to find out whether the supplier provides technical support.

Freestanding or Attached?
Having a greenhouse connected right to your home has many advantages - especially if you want to grow year-round. You can wander in and out to see what’s happening at any time, day or night, no matter what the weather. With your plants so close at hand, it's easier to remember about watering and other tasks. Access to water and electricity is also easy. On sunny winter days, an attached greenhouse can add a significant amount of free heat to your home.

But attached greenhouses have a few downsides as well. Without proper venting and a way to isolate the greenhouse from the rest of your house, it may make your home too warm in the summer, and can keep your furnace running day and night in the winter.

Freestanding greenhouses are usually less expensive than attached models, and are much easier to set up. They can be placed right on the ground (though if you intend to heat the greenhouse through the winter, you should consider insulating the foundation down to the frost line). If you will only be using your greenhouse seasonally, a freestanding model will be relatively out of sight during the “down-times” of midwinter and midsummer. Putting in access to power and water may be relatively costly, and many greenhouse gardeners get along just fine with an extension cord and a garden hose.

Classic or Modern?
You will probably want to ensure that the shape or style of the greenhouse is compatible with your home. Even the most elegant Victorian-style greenhouse will not make an attractive addition to a New England saltbox. Northern gardeners must also consider snow load when choosing a greenhouse.

If snow doesn't slide off the roof naturally, you'll have to shovel it off to protect the glazing and allow light to enter the greenhouse. The overall shape of the greenhouse also determines the interior space and how it can work. Make certain that the style you choose provides enough headroom, wall area for displaying plants, a work area and enough roof area for venting.

Glass or Plastic?
Glass is still the traditional choice for greenhouse glazing, but there are now many high-quality horticultural plastics to choose from, including polycarbonate, acrylic, polyethylene and tedlar. When selecting a glazing material, you need to consider appearance, lifespan, whether you need single- or double-glazing, how weathertight your greenhouse needs to be and, unfortunately, price.

Traditional multi-pane glass greenhouses are notoriously difficult to seal. Modern attached greenhouses, with large panes of insulated glass, are usually very weathertight. If you live where the ground freezes, a glass greenhouse needs to sit on a permanent foundation, or frost heaves could break the glass. Glass lasts almost indefinitely, and its light transmission is very high.

That said, plastic glazings offer some distinct advantages over glass. They are far more forgiving of temperature fluctuations. They are easier to handle (lighter weight and non-breakable). They diffuse incoming sunlight, which prevents leaf-scorching. Last but not least, they won't be shattered by an errant frisbee or softball.

Gardening in a greenhouse
Owning a greenhouse can give you the opportunity to grow plants from all over the world. But before you stock up on potted citrus, orchids, cacti, scented geraniums and bromeliads, you need to stop and think about what sort of growing environment you will actually be able to provide. A common mistake made by beginning greenhouse gardeners is to fill the greenhouse with any plant that piques their interest.

An eclectic assortment of plants such as this may look fine for a few months, but they will soon begin to suffer. Some plants need cold nights, some need warm nights. Some like lots of bright light, some require filtered shade. Some need water twice a day, some only every few days. The challenge is to decide what sort of environment you will be able to provide, to take advantage of the microclimates within the greenhouse, and to choose plants that will thrive in those conditions.

If you plan to run your greenhouse year-round, you first need to determine what temperature range you want to maintain - both in winter and in summer. Wintertime temperatures ranging from 40 to 60 degrees F may be ideal for growing salad greens, herbs, camellias and for overwintering tender exotics. But these temperatures are too cold for producing healthy tomatoes, gardenias and tuberous begonias.

During the summer months, bright sun and daytime temperatures of 85°–90°F may be fine for potted tomatoes, bananas, figs, and geraniums, but alpine plants, African violets, and many types of orchids will not tolerate the heat.

Microclimates
Within any greenhouse, there are certain areas that are hotter or cooler, brighter or shadier. By taking advantage of these natural microclimates, you can provide optimum growing conditions for a wider range of plants. Shade cloth, lathe, small fans, propagation chambers, heat mats, and other devices can also be used to help create and manage these microclimates.

Your climate, the type of greenhouse you have, and the amount of time and money you are willing to invest in heating and cooling, will determine what sorts of plants you'll be able to grow successfully.

Resources
Favorite Books
Greenhouse Gardener's Companion by Shane Smith (Fulcrum, 1993).

Greenhouse Gardening by Miranda Smith (Rodale, 1985).

Planning, Installing and Using Greenhouses (Ortho Books, 1991).