Don't cut the buddliea, baptista, or agastache until growth starts in spring; they are subshrubs or woody perennials and do better if left to resume growth before being cut back.

No need to cut back azalea unless it is too large for the spot where it is growing, or unless you want to shape it into an unnatural form. These look wonderful, to my eye, in their untrimmed, somewhat irregular, form.

Most people leave ornamental grasses through the winter, they can go through some interesting phases as the season progresses. Hosta can be cut almost any time, I like to do it after a true hard frost but before they become mushy from repeated freeze/thaw cycles.

Spirea does not need to be cut unless it's got a lot of seed heads, I'd remove them since *some varieties of these* can become pests in some areas. Yours does not look like an invasive type, and since its form is very nice, I'd leave it alone.

I don't grow chelone, so I can't offer any advice on that one.

Another reason to leave your azaleas alone is that they have already formed next year's flower buds. You'd prune your spring display away.

I have experience with daylilies and hostas that I can share. As soon as all the leaves are yellow and turning to mush on both plants I start trimming off the leaves. Then I normally wait however long after that for the rest of the leaves to just lay on the ground due to cold as diggingthedirt said. My daylilies look just like yours at the moment and should be fine. My hosta leaves have all been removed and composted for a while now and you won't see anything above ground again until next spring.

Hope this helps.

Kate

It's better to leave the chelone growth standing so it can help the plant survive the winter. In early spring, you can easily remove the dead stems.
The Veronica you can cut to the ground, as it turns black if left until spring.
You can cut back the Baptisia, as it will turn black with frost, although some people leave it standing.
You can leave the agastache until spring, although I always cut mine down in fall to limit reseeding. It does get woody, but mine always grows back substantially regardless of shearing it down.
Yes, leave the buddleia until early spring.
On the ornamental grasses...I try to leave them through winter, but by Feb they are shot, so I trim them down when they get ratty in winter, or leave them until early spring if I'm busy.
Hosta...as much as I want to cut back hosta because the leaves die with frost, leaving them does add protection to the plant during winter, as some hosta varieties benefit from winter protection.
Spirea...you can prune Spirea japonica in early spring, as it will flower better on all of the new growth put out. You don't have to prune it, though. If you have a younger Spirea, then it would be best to leave it for a few years before pruning. It looks good, as mentioned.
I do put shredded leaf mulch around my perennials for winter protection.

Last year the maintenance guy at the local school decided on his own to severely cut back the azalea shrubs in November as his way in helping me out in the gardens. The only problem was that he cut away all of the blooms for spring, so we had not one flower amongst our azalea shrubs. Prune azalea right after flowering, if needed, in spring.

You might want to remove the spent blooms on the buddleia and agastache's to prevent heavy reseeding. I keep my buddleia's deadheaded throughout the season, and always whack my 7'er back to about 4' now, then as far back as I can in the spring. It's over 10 years old and has a huge trunk, so it can't be pruned back lower than 2' anyway. I've pruned it both in winter & in spring, and it always comes back. If you're a bird person, the goldfinches would probably love you for leaving the heads on the agastaches, but come spring time, you'll probably have loads of seedlings (all in the wrong place, like me!).
As for the daylilies, I don't think it matters when you whack them back, but like most bulbs, you shouldn't cut them back if they're still green. Considering it's hard to kill a daylily (IMO), you should be okay. Same with hostas; I can't kill mine.
I tend to leave my few ornamental grasses up; I like to see them poking up through the snow.
Azaleas should be pruned right after they bloom; never much later (see rhizo's reply).

In general, perennials are cut back in fall unless they offer winter interest, e.g. certain sedums, ornamental grasses. If your agastache is one of the western, dryland species, don't cut back until spring. If it's A. foeniculum (blue flowers), it's completely hardy and can be cut back in fall.

Azaleas and spireas are shrubs. The former should never be "cut back" though they might need minor pruning in spring after bloom. Some Spireas are cut back after bloom to encourage fresh growth, but not all.

What you need are a couple of good basic books on perennial and woody plant care.

Laceyvail is right about the agastache - the western types really suffer from being cut back in fall. Blue Fortune, the most common of the blues, should not reseed, being a sterile hybrid, but the species (A. foeniculum) will throw an annoying number of new plants no matter what you do.

When in doubt, wait until spring, as the number of plants that really need to be cut back in fall (peonies, for example) is very small compared to those that do better if left alone. Aside from the subshrubs, many marginally hardy plants get some sort of protection from their dead stems, though the mechanism is not always clearly understood. You also provide winter shelter for birds and other wildlife when you leave some perennials standing over winter.

The only perennials I cut back in fall are peonies and lilies, true lilies, not daylilies and anything that had a disease or pest problem.As diggininthedirt said in many cases the stems help to protect the crowns of the plants. Do you ever see mother nature cut back wildflowers? Personally I have a difficult time understanding the obsession people have with cutting things back in the fall. To me the spent foliage is part of the natural cycle, I also enjoy seeing the branch structure of trees and shrubs when the leaves are off, while many people see ugly bare branches. To each his own. By the way your unidentified ornamental grass looks to be some variety of miscanthus.

I agree with hostaholic2...
By this time of year most of the gardens in the area look like a crop harvester got lost on its way to the cornfields and razed the gardens instead.

Dear coeng,
I enjoyed your photos of your beautiful plants. Great garden. Being a newbie, I was glad you asked this question.

coeng, I don't cut back any of my perenniels in the fall unless I've had a disease problem with the plant. We don't get a lot of snowfall here in the St. Louis area and letting the plants stand helps to trap leaves and insulate the crowns of my plants. I only cut back the longest canes on my roses so the wind doesn't whip them around. Anita

There is no good reason to cut things back in the fall, unless you have a disease problem. This is especially good advice for a newbie since some things manage to stay green even in z5.

The uncut plants will hold more snow which protects the plants. Some say that it even keeps water out of crowns - but I am not sure I buy that reason.

And the best reason for waiting for spring is that the weather is better in the spring to do garden work.

I've found that perennials that still have their leaves are less likely to suffer from heaving if we have freeze thaw cycles, since the ground right around the plant is less likely to thaw (even though all of my garden is mulched.) Also, on some of my plants I leave seed pods for the birds. Throughout the late summer and fall, and then often late winter I get birds visiting the garden to eat seeds, but I don't leave the seedheads on plants that are problem reseeders.

I basically agree with Hostaholic and the others too - I cut down or pull certain plants in the fall, but leave most of them standing. Peonies and any others that have disease or fungus are cut down. I also cut down the Lilies. Some of the scraggly, uglier annuals are removed, but others stay.

The enjoy watching the foliage and seedheads change through the fall. Some perennials provide seeds for birds, or habitat for beneficial insects over the winter. The dead foliage will catch the leaves and hold them in place, which is what I use for mulch over the winter (and then add compost/shredded leaves in the Spring).

I also enjoy the winter interest. If you looked out my front door a few days ago this is what you would have seen. There is over a foot of snow on the ground here and we got yet another 4-5 inches today! I love to see the dead foliage of the shrubs and perennials and the arching stems of the grasses.

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And this is what the same garden looked like this past July:

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