I say leave them there to rot. The only concern is if they're diseased or infested...

If you run over them with the mower you would be squashing the soil in the flower bed, which is a no-no. Basically you should never step on or compress your garden soil. I leave mine in place, it depends how tidy you want your garden to be, there is no reason to remove them, I think it is better for the soil to let them rot in place without being disturbed. They will decompose well over the winter.

Marcia

If you remove those dead plants you remove the nutrients they had from that planting bed while leaving them in place will allow your soil bacteria to recycle those nutrients right there. Pulling them up and composting them is one option, but that means pulling them up, hauling them to the compost pile, working the compost pile, digging in the compost pile and hauling the finished compost back to the garden, a lot of unnecessary work.

Instead of mowing over them, try a "weed wacker". Works well to get them to soil level without putting too much weight on the bed soil.

Like rdak, I usually just chop them off and lay flat on the bed, letting the roots rot in place to feed the soil and laying the tops flat on top of the soil like more mulch. I always hope that they'll drop their last seeds in place to form volunteers. I do get some volunteer petunias occasionally but never impatiens.

In spring those roots easily come out without much effort at all.

Anything that is obviously diseased (the horrid summer weather brought a lot of powdery mildew this year) I trash. Some probably make it to the compost bin but since I'm not sure the compost is always hot enough to kill all pathogens I try not to get much of it in there.

Karen

Thanks for the replies. I will go over them a bit with the weed whacker perhaps.

Will the roots eventually have to be pulled out, or will they decompose by spring?

Most definitely, remove such garbage and deposit into your compost pile.
Such rotting material has no place to be kept in a garden.
Insects and disease are rampant visitors to such garbage and will in no time, start to raise a family there.

The best thing you can do for your garden is Keep it clean.

Ah, jeannie7, that login rings a bell as someone who has very strange gardening opinions. Leaving the roots in place is RECOMMENDED by many, as it disturbs the soil structure less. It is especially important with plants like marigolds or peas where the roots have something to add to the soil, e.g., nematode resistance or nitrogen nodules. Plant material is NOT garbage, and does not bring rampant disease to your garden unless there is something in particular wrong with it. I can attest to this, as I am a very 'leave it alone' kind of gardener, that being easier and me having 5 acres to watch over. We don't rake most of our leaves, either, guess what, no dread disease or horrible creatures. (We did see a fox walking through the yard today, that was cool.)

The idea of keeping a place full of dirt "clean" is kind of funny anyway. Keeping the soil covered with some kind of plant mulch is very helpful over the winter, too, so that there is less erosion and you give some food and cover to the beneficial bugs and worms.

Marcia

There is no good reason to remove the roots since, if you have a good, healthy soil with an active Soil Food Web, they will get digested and add the nutrients they removed from your soil back into your soil. There are some people, with unhealthy garden soil, that will tell you that you need to remove all plant debris from your garden to prevent disease, but like us plants tand to wnat to grow strong and healthy and will if given a chance (grow in a good, healthy soil) they will resist diseases quite readily. Plants trying to grow in unhealthy soils will be stressed and more susceptible to plant diseases.

Just like all of the leaves you mulched in place, leave them. Organic material is a good thing in the soil. I wouldn't even bother with the weed whip unless the looks bother you.

Leave them, and call it "winter interest"

It always strikes me funny that so many publications on gardening conflict themselves by saying to mulch with organic materials and yet clean up and dispose of all organic materials. How do you do both?

If something is obviously diseased, then it is reasonable to compost it or perhaps dispose of it. Otherwise, it makes much more sense to leave things in place to rot and diversify the soil life. And in some cases depending on the disease, leaving the plant material in place to rot is not likely to affect things one way or the other due to the nature of many of the diseases. Nematodes may be the exception where they feed on the root materials but crop rotation and lots of organic matter are the keys to that at least in short term crops (with trees you may need to plant resistant varietys.)

I leave my petunias in place over winter, especially the wave petunias. They help hold the leaves in place.

tj

I did not bother to pull out my marigolds. They were planted on a hilly slope and I was afraid that pulling them out may lead to soil erosion over winter due to heavy rains.
But when I read somewhere that leaving decaying plants in the garden over the winter invites wintering over of diseases and particularly increases insect and pest population I was concerned.
Now I am in a dilemma.

Regina, In nature, nobody cleans up the dead plants in the fall. Unless you have a really bad disease or pest, they'll be fine.