After a couple frosts in the fall (end of Sept or in to Oct) and your plants are dying you can start to get you raised garden bed ready for winter. Our focus is on creating living soil that will naturally feed your plants. Living soil is teaming with microorganisms, worms and other insects which turn your soil into soluble food for your plants. By adding compost, manures and mulch you are feeding and keeping alive these important communities of microorganisms, fungi and bugs in the soil: Living Soil! Following these steps:

1. Remove weeds and put in compost.
2. Remove stakes and trellises.
3. Clean up dead plants and put in compost. Chop large plants up so they will breakdown easier in the compost.
4. A good time to collect seeds for next year. You can leave some of your plants to go to seed and collect the seed before composting. Dry in a paper bag, or on a plate in a warm dry place. Some plants like arugula, you can take the plants in bunches and hang to dry. Taking the seeds from the pods once dry.
5. Add about 2 inches of compost and other organic material; worm castings, composted manure, compost to you bed, no need to dig it in. Your plants next spring will love this!
6. Add another couple inches of mulch on top of the leaves, straw, grass clippings. If no mulch available cover with jute coffee bags from Kicking Horse Coffee or even plastic. Hold down with rocks, bricks, wood or pots of soil. You can also put these bags over your mulch to hold it down and so it won’t blow away.
7. Take care of perennials. … the perennial beds plants at each site could use weeding and cutting back. If you have herbs in your raised bed that will overwinter, leave in the garden and mulch around them.

A mantra of the serious gardener is never to leave bare soil. One of the simplest techniques for making sure soil is protected and enriched is using mulch. “Mulch creates a great environment for the development of soil biology,” Kempf says. “When we mulch the soil, we get good levels of biological activity, nutrient availability and aggressive plant growth the following spring.”
Mulch is a blanket that protects plant crowns and roots from the extreme temperature fluctuations of winter. One of the best mulches is a good snow cover, but even very cold regions occasionally have winters with little snow. Thus it is important to mulch with plant material that does not compact and retains a certain degree of “fluffiness.” Chopped leaves work well, as do straw and grass clippings.
Website for more info:https://hellohomestead.com/how-to-prepare-a-raised-garden-bed-for-winter/ There are lots of great videos online. Search around and find one that speaks to you.