As a naturalist and a teacher, gardening and teaching about plants is part of my curriculum year-round.  Even in winter, there is still a lot to learn from a garden.  The following activities can be used year-round, depending on what the climate is like where you are. 

Growing seedlings is a great project for the winter months.  Garden supply stores sell peat pots year-round, and many varieties of small tabletop greenhouses are available.  Choose seeds from packets, plants you already have, or gather some from nature walks.  If you eat organic fruits and vegetables, you can plant the seeds from your food.  Non-organic fruits and vegetables are most likely not viable.

I have planted everything from corn to apple trees using peat pots, and my preschoolers love this activity because they get their own plant.  They watch it grow, water it, and it's different from student to student depending on what they chose to use for a seed.

Once the seedlings get old enough, transfer them to bigger pots.  When it's warm enough outside, you can plant them in the ground. 

Kids love to ask questions.  Encourage them to ask what different plants are, and have a picture guidebook handy so they can look things up themselves.  For pre-readers, help them to find the plant, then read them the name and characteristics.  Next time you see that particular plant, ask them what it is.  They'll be proud to answer! 

Ask the child what he or she wants to grow, and help them plant their favorite foods.  Show them how to water each plant and monitor how it grows.  Depending on the child's age, adult watering and monitoring will be required.  Teach the difference between good plants and weeds, beneficial insects and pests.  When it's harvest time, show the child how to pick their food, wash it, cook it (if needed), and eat it.  Mealtime is more fun if it's something you've had a hand in creating! 

Picking berries is mainly a summertime activity, but there are berries and nuts that grow year-round in some climates.  Grab a bucket or two (or three or four) and head to the nearest bushes!  For added fun, cook something from your harvest. 

If you don't have much space, you can still garden.  Many garden stores sell "strawberry pots" or other container garden pots.  These can be used for berries, tomatoes, herbs, flowers, and any other plants that have shallow root systems.  They are also great for indoor gardening from fall to spring, or for a child's room.