Collect empty plastic milk jugs throughout the winter and keep them clean and dry. When you are ready to winter sow, grab some scissors or a box cutter!
Use a well-drained potting blend that is rich in compost and a drainage material like perlite or vermiculite. Pre-wet the potting mix until it is about the consistency of a wrung-out sponge.
Cover the lid of the milk jug over the bottom portion and use packing or duct tape wrapped around the center to keep the jug shut. Don’t use too much tape because you need to open this “greenhouse dome” in the spring when the weather starts to warm and the plants need more ventilation.
You can leave the winter sown jugs outdoors without any protection. All you need to do is check the soil moisture every couple of weeks leading up to your expected last frost date.