A greenhouse can be a great resource for growing feed for your rabbits during the cold months. Here are a few options you can consider:

1. Wheatgrass: Wheatgrass is highly nutritious and can be grown easily in a greenhouse. Rabbits enjoy eating wheatgrass, and it provides them with essential vitamins and minerals.

2. Barley: Barley is another suitable option for growing in a greenhouse. It is a fast-growing grain that can be harvested and fed to your rabbits. Make sure to sprout the barley before offering it to the rabbits, as this enhances its nutritional value.

3. Alfalfa: If you have enough space in your greenhouse, you can grow alfalfa. It is a nutrient-rich legume that rabbits find particularly tasty. Harvest the alfalfa when it reaches the desired height, and feed it to your rabbits.

4. Rye grass: Rye grass is a cool-season grass that can be grown in a greenhouse during the winter months. It provides rabbits with a fresh and leafy green option for their diet.

Ensure that the feed you grow in the greenhouse is free from pesticides or chemicals that could harm the rabbits. Monitor the growth of the plants, provide adequate water and light, and harvest them at the appropriate time to maximize their nutritional value for your rabbits.