A greenhouse requires an initial, upfront cost, but over time you will recoup that cost and then some. Growing vegetables and fruits in a greenhouse allows you to create the right conditions to make it easier to get a greater yield of produce, including out of the season foods so you don't have to pay high grocery store prices.Keep out pests. The bane of every gardener's existence is the ever-present threat of pests. For vegetable and flower gardeners, the threat of rabbits, raccoons, deer, and other critters is real and persistent. Protect your plants with a greenhouse and you don't have to worry about pesky nature again.Starting seeds. For the plants you begin by seeds and transplant to the garden, what better place to do it than in your very own greenhouse? With year-round warmth and protection, you can start seeds and tend to transplants whenever you want, and you won't have to fill your basement, garage, mud room, or wherever you normally start seeds, with pots and soil and general messiness.A cozy retreat in winter. The positive effects of greenhouse growing are not limited to the benefits for your plants. You, too, can enjoy your greenhouse. Just imagine a cold, snowy winter day and stepping into your own warm, tropical oasis filled with growing, thriving plants and flowers.Okay, so by now you've learned all about the potential positive effects of greenhouse growing, but before you get too comfortable and jump right in, consider the following cons of growing in a greenhouse: High upfront and operating expenses. Well, it is certainly a "green idea" in that it is going to cost you some green - money, that is. Depending on the type and style of greenhouse you are considering, you could be spending several hundred or even thousands of dollars. You must ask yourself, "How long is it going to take me to see a return on this upfront investment - is it worth it?" And, it's not only the upfront investment that should be factored in.Temperature and air circulation are constant concerns in a greenhouse and may require additional purchases, such as fans and heaters, in order to regulate. And let's not forget your gardening supplies either. All of this adds up. In a greenhouse, Mother Nature also isn't directly watering your plants, so you are going to undoubtedly consume more water unless you have a rainwater collection system in place. All of these are greenhouse disadvantages and will have an impact on your utility bills which, in turn, is not such a green idea from a conservation standpoint