If you only use organic stuff in the spring, it's not an issue.
Depends on what you are putting on. I do feed bone meal to newly planted bulbs in November when I plant them, but I wouldn't feed anything that I wanted to "go to sleep" after the end of July ....and remember....anything you put on will feed for about 6 weeks.
As I have said many many times, more plants are killed by too much fertilizer than by too little. When in doubt, don't!
Linda C

Suggestion, in NYC I learned that I need to stop fertilizing after 1 September or 1 August, depending upon the plants. Good luck.

None of the perennials you mention need to be fertilized on any regular basis. Fertilize, if you want, in spring and perhaps lightly after you cut them back following bloom.

In Tracy Desabato-Aust's book, she says to fertilize astilbes with a higher nitrogen ratio, as is lawn fertilizer. She says when fertilizing the lawn, throw some on your astilbes, too. This should be done around mid Sept. to October 1.

I haven't followed this advice yet, so can't comment on how it works personally, but her advice is pretty well respected.

I would stop right about now. You don't want to encourage a lot of new growth just before it gets cold. Many perennials are done for the season at this point and fertilizer isn't going to help. One exception are bulbs. I sprinkle bulb fertilizer on my bulb beds to feed the bulbs in the fall, including lilies after the stems have died back. I spread compost on my beds in late spring so I don't need to fertilize. Compost and organic matter added to your beds regularly are better than fertilizer anyway so you might want to get into that habit every year.

As a side note, I fertilized my Dahlia back in late July. Since then, it has developed tons of leafy foliage and NO BUDS! Did I fertilize too late?

Most dahlias don't start blooming until late July and after. Next time, start fertilizing the dahlia earlier, but it's better late than never. You should get buds very soon. Annuals are different than perennials. You can fertilize annuals a lot longer and more often (if you wanted to) - their entire lifespan is over and done with in one season.

So what would that mean for annuals in a container garden? Would you fertilize them right through September?

Annuals don't go dormant....they die....so feed them right to the end....if they are plants that grow best in a rich soil.
Linda C

I don't fertilize anything in my garden with commercial fertilizer except roses and clematis. These get an early spring application of slow release rose fertilizer and then another application immediately after blooming, if they are rebloomers.

Most other perennials in my garden get topdressed with organic mulch or chopped leaves on an annual basis, or sometimes with homemade compost or bagged humus & manure, if an area needs pepping up a bit. I also have one gravel bed which receives no amendments which I use for plants that prefer thin non-fertile soil.

On your list of plants the only plant that I might consider fertilizing is the astilbe. They are heavy feeders and like a rich soil with many nutrients. I would still prefer to do this using natural garden products, rather than commercial fertilizers. What you need to do is feed your soil, not fertilize your plants.

And I am sold on alfalfa meal or pellets..it's just magic!
And I do feed potted stuff about mid season with "chemicals!" LOL!

Linda, what plants do you use the pellets for? I am going to try it next year. Do they sell them at Lowe's? Or a nursery?

I use alfalfa pellets on everything...
I buy it at my loacl feed store...which specializes in animal feeds and seed and fertilizer. I pay about $10 for 50 pounds. I just liberally toss it around in the spring and again about mid June.
This year I am going to try tossing some on thin spots in the lawn around mid September.

Here is a link that might be useful: roses and alfalfa