Yes. Organic matter, those kitchen scraps, are digested by the Soil Food Web, all the wee critters from earthworms to bacteria in the soil, digest and convert to nutrients the plants can use. Some here will say that organic matter "disappears" and in a way it does as it is made into something plants can use and therefore organic matter needs to be continually replaced as you are doing.

Yes, and it's something a lot of people don't get; I can't figure out why, as it seems so obvious. Isn't it better to have an entire garden of rich soil rather than little pockets of it?

And besides, it's an easy way to use the nutrients in your kitchen scraps while skipping the composting step. Just smile and keep on doing what you're doing.

I think you can do this as far into the winter as you want and are able to. Around these parts (Midwest) it gets too soggy and then it freezes up, so no digging after about Thanksgiving for me. YMMV.

One way to keep trench composting all winter is to dig the trench in late fall and cover the dirt with something to keep it dry. Dump in the scraps and cover with some of the protected dirt.

I do it at first frost, and when the ground thaws in March. It is work, so it is not something you can do every week, and I do it only on ground that has been cleared of plants. For perennials, there is always wood chips as mulch.

Thanks to everyone for your suggestions.

My first question concerned how long I could continue digging in scraps in areas where I planned to plant perennials next spring. I assume that decomposition will greatly slow down as temps drop. If this is the case, might those areas still contain a lot of non-decomposed material? And would it be advisable to plant in such an area?

I have found the contents of those 'pockets' of scraps will mostly disappear within a few weeks depending on what the scraps contain and the temperature. Onion peelings and pits stay around longer. However, I've been doing this a long time so have lots of tiny organisms and worms which feed on them.

Gardening is often IMO a big experiment so you might continue as long as possible and see what happens. Worst scenario is that you might have to move some onion peelings to another place. Also you could throw a handful of alfalfa pellets into that hole when you plant which provides nitrogen.

If it's just kitchen scraps I don't think there would be any problem with planting on it almost immediately.

If there's an open spot, I dig in my weekly can of garbage, and not very deep at all. If there's not a spot open it goes onto the pile for the birds to mess with. As luckygal said, these little pockets of rotten food disappear very quickly. I am still surprised to find so few traces in the dirt.

Thanks.
Along with the solid scraps (peels, old bread) I always seem to have a lot of soft stuff (pie, cake, beans) which I "squish' so that I end up with what I'd call a 'gummy mess'. Always looks like I've poured a gallon or two of bread pudding in the hole! I'm thinking those worms will like that as well as the solid stuff. I am just hoping that, should I still be doing this next March, it will have had time to decompose.
Thanks again to all for your constructive and encouraging words.