At our latitude, Feb. 11 is the date that greenhouse workers once again notice that plants come out of dormancy and start growing. From then on it becomes hot and humid in greenhouses on sunny days, including cold days.

The awakening in Minnesota greenhouses on or close to Feb. 11 each year can be attributed to this: The sun is higher in the sky, concentrating its rays. There is some connection to our cars and trucks: Even on cold days the interiors now warm up when vehicles are parked in the sunlight. The rays shining through windows, warm the dashboard and seats, which in turn warms the interior air.We also notice snow melting on dark surfaces when the air temperature is below 20 degrees.

Between now and the end of March is a good time to prune grape vines. Orchardists continue to prune apple trees. I have pruned many apple trees and found that winter weather helps tree wounds heal more rapidly. Seed and plant catalogs have been arriving in the mail. Colorful displays of vegetable and flower seed packets are on display in some stores, and many of us have begun planning for the upcoming gardening season.

The brown-colored red oak leaves that have clung to trees since last growing season have been falling, another subtle spring sign. Bunches of boxelder seeds provide visual interest throughout winter and supply nutritious food for squirrels and a variety of hungry birds.

Great horned owls are on nests incubating eggs. They are Minnesota's earliest nesting bird. Bald eagle nesting time has started, and some pairs have already returned to old southern Minnesota nesting sites, and have been seen adding sticks. A few begin laying eggs this early. By mid-March the mating season has started for squirrels (flying, fox, gray and red) and also for red foxes.

Jim Gilbert's observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.