What I normally do is add a layer of compost and then either mulch or plant cover crops. Probably better things you can do than add weed barrier.

I usually add compost and cover with cardboard with a few holes stabbed in to let water through. Nancy

I too add compost to most beds and the a few inches of fall leaves.

Bare minimum I chop up what grew there before to try and incorporate into the soil and add a thick layer of straw. If I can, I like to add compost before the straw. If I have a good plan developed for the next year, I might do something like add the scrapings from the chicken coop to a bed where I know I will be growing something that can handle it, like melons or cucumbers.

Compost can be added anytime if it is truely compost. Keep in mind that most added nitrogen will be leached out of soil by spring.Your best option going into fall is a cover crop and tillage radishes are a very good choice.

Just FYI on the tillage radishes that Barrie mentioned. They need to be planted a couple months before your first frost date so they have time to get the nice 12" - 18" roots before they get frozen out. Also be warned that they stink pretty bad when they start to rot during a warm spell in the winter. By spring your garden will have lots of 2" diameter holes and lots of radish carcasses scattered about.

Cover crops are best. I like oats, they winter kill and can be incorporated in the spring to add biomass. I use radish (with clover and vetch) in areas that are bare by late August. During September I plant a mix of oats, vetch, clover and field peas. I plant Crimson clover in areas that won't be used in spring. It will go dormant over winter and flower in the spring. By October it is just oats, maybe rye. Rye will grow slowly in the winter. Everything but the clover should due over winter.

I notice that the cover crop suggestions seem to be coming mostly from people with cold winters. In a small garden in climates like mine there are crops in the ground nearly all the time and not much time or space to sow a cover crop in the Autumn. In addition, the winter won't kill the cover crop so it needs to be cut down and dug in in the Spring. More work. So I just go with compost.

That's a good point about winter prep in warm climates. Cover crops don't make a lot of sense down here. If you're not going to do winter veggies, a good possibility may be to dig in uncomposted materials, like ground leaves, and do in-situ composting for many months. Might be smart to mulch with it as well, to suppress weeds.

Here's a concern: if I prep the beds for winter with leaf mulch etc, what happens to the possibility of getting volunteer plants? Nothing will reseed right? I was hoping not to have to seed parsley, cilantro, lettuce in the spring and just rely on reseeding.

Mulch will suppress weeds and volunteer plants as well. If you WANT volunteer plants then I guess you'll have to scrape the mulch off when you expect them to come up. Not really sure about the best strategy if you want volunteer plants.

I think mulch might actually be a good thing for some seeds. I'm in zone 5. Cilantro readily self sows in my high tunnel but not at all outside. I wonder if it might re-seed if my outdoor bed was protected with mulch which would be removed in the spring. Despite digging over a bed, adding more soil and fertilizer, kale grew here and there among straw mulched potatoes. It came up through the straw. My garlic bed was mulched in the fall of 2016 after planting and harvested in late July. I left the straw in place. I have calendula and dill that have grow up since July. It doesn't matter how much I work the soil (usually a thorough forking and running thru the surface with a hand weeder on the narrow beds, calendula and borage grow all over the place. Nasturtiums, claytonia, kale and arugula self sow in the high tunnel. Despite heavy weeding on multiple occasions, a really nice alyssum grew where seed had fallen from my hanging baskets. I have to pull up calendula and borage because it grows so thickly. Everything will re-seed better without mulch but I don't think mulch will completely zero out your chances.

I think I'm going to save some seeds from those plants just to be on the safe side and then mulch. I'm sure benefit of mulching is too great not to do it and throwing some seeds out myself in the spring is not too hard.