I do most of the work in the winter. My old neighbours used to ask how we kept it so good as we never seemed to do anything, that's because we used to go out when they were tucked up in front of the fire.
Raking, pruning, turning compost, mulching, cutting back, digging out, planting new trees, making new beds, weeding, turning compost again (do it regularly and you will have good company for the spring), moving captured water into storage butts and containers, putting framework in for the next year's beans and peas, cleaning polytunnel and greenhouses, growing winter crops, harvesting witner crops, planting garlic and overwintering onions in October, collecting and mowing leaves for leaf mould in November, sowing onion seeds in December, sowing chillis in January, sowing tomato seeds in Feb and before you know it, winter is nearly over.
If you just grow one crop all winter, try spinach and harvest every week and you will have lovely fresh greens for your soups and stews. I've already sown my first batch of winter veg, kales, kohl rabi, parsley, spinach, Chinese cabbage, beetroot. I'll be doing another sowing of more when I source more seeds.
It's not just a summer hobby it is year round!