If you have the space in your yard, adding a greenhouse gives you a world of possibilities. Tangible advantages include allowing you to grow crops over the winter, giving you an early start on spring planting or providing space for bulky projects like worm bins. Then there are the intangible benefits for your soul--having a dedicated spot for garden puttering and for enjoying a warm (or at least not freezing) space filled with growing things.
Extend the Growing Season
Although there is no guarantee plants in a greenhouse won't freeze during cold spells, the amount of damage they will sustain is far less than what they would face directly outdoors. A greenhouse will extend the growing season by many months. For instance, if frost presents a danger and tomatoes have not all ripened, simply bring them inside the greenhouse.
Grow Plants All Year
Plants that are cool-weather crops to begin with do well in a greenhouse over the winter when they are planted during the fall. Most leafy green vegetables fit that category. Spinach and kale, for instance, are both very tolerant of cold temperatures and can be sowed several times over the winter. Other cool-season vegetables to grow include chard, broccoli and green onions.
Get a Jump on Spring
If you don't have room in a greenhouse to over-winter all the more tender outdoor plants, you can still use a greenhouse to hold over plants or for rooting stems to replant in the spring. For example, geraniums do well overwintering either as rooting stems or in a dormant stage with many stems in one pot. A greenhouse also is ideal for starting seeds or for allowing seedlings of plants like tomatoes or peppers to grow and strengthen before being planted in the ground.
During the winter, some gardeners use their greenhouses as evening shelters for chickens who forage outside during the day. The chickens provide an added benefit in their caged-in area by ensuring that greenhouse temperatures won't fall below freezing. Or stash away a worm bin or two in the greenhouse. The worms can go about their business producing compost for the garden without you worrying about them freezing.
Inspiration and Relaxation
Having a dedicated space for potting benches, hanging racks for tools and perhaps a sink is a dream for some gardeners. A greenhouse with these amenities makes it easy to try new plants or propagate favorites to give to other gardeners. Imagine having a place for all your gardening tools and a space to grow more difficult plants like begonias, gardenias or Meyer lemons.