Ok, you've put a lot of effort into planning and building (or installing) your greenhouse. You've got tabletops, benches, pots, shelves, cabinets, watering systems and a dozen tools to help. Now, you get to really enjoy what greenhouses are all about - plants!

The 'green' part of greenhouses is usually the most fun, since that's why you get one in the first place. But here, too, you'll want to do some planning and careful execution. That planning should start at the same time as that for the greenhouse itself. The structure and its contents should be well matched for optimal results.

Fortunately, you've got hundreds of choices.

Consider first where you live. Even in a greenhouse, the amount of sunlight per day throughout the year, humidity and temperature levels and other variables need to be accounted for.

Northern Idaho, for example, has long, dry summers. New Hampshire, even though it's also in the northern latitudes and gets about the same amount of rain and sun, is much more humid. You can only control humidity to a certain level.

If you get plenty of sunlight in the summer and early fall, or can compensate with artificial lights, tomatoes love greenhouses. The high heat makes them grow great and, since they are easily injured by frost, they appreciate the protection in the Fall.

Some citrus fruits, like oranges and lemons, are nearly impossible to grow outdoors in certain locations. It's simply too cold much of the year. But you can compensate in the greenhouse and actually grow your own.

Strawberries are another favorite for greenhouse gardeners. Commercial strawberries are expensive and many people have concerns about pesticides. You can grow your own and control costs and quell health concerns.

Radishes, onions, carrots, lettuce and spinach like cooler temperatures. They can really do well in a controlled environment like a greenhouse.

Then, of course, there are the traditional 'hothouse' flowers - orchids first and foremost. Orchids in the wild grow up higher because they benefit from the breezes. You can simulate that in the greenhouse with a simple fan and ventilation system.

Orchids can also be very expensive and growing your own can be a great way to save money and still have beautiful flowers. For the truly ambitious, there are dozens of competitions across the country for orchid growers. Be careful of getting bitten by the 'orchid growers bug', though. It can turn into an all-consuming hobby!

But lots of other flowers make great choices for greenhouses, too. Practically anything you would grow in an outdoor garden will do fine in a greenhouse, provided you have proper sunlight and shade control. Keep in mind, too, that some plants don't do as well in pots unless they are large enough that the roots have plenty of room to spread.

Most bonsai are outdoor plants, though some benefit from the protection of a greenhouse in high winds and cold winters. Take care that the species you select is suitable for a high temperature, high sunlight and humid environment.

Sooner or later, though, it's time to stop planning and start gardening!