I live in Zone 3 and I plant up to the middle of September (cheapest time to buy plants from the nursery). I cover the new and more delicate ones with grass clippings and leaves in the fall to help protect them.

Many of the well known garden gurus in this area believe that it is okay to plant perennials in early fall. I personally have found no problems whatsoever when planting perennials all through the month of September and even into the first weeks of October.

The soil here is actually quite a bit warmer in September than in our naturally coolish and wet springs. My heavy clay is not really workable in early spring, so spring planting often becomes early summer planting. As a result of that I often plant in fall. The ground does not freeze here until mid/late November, sometimes mid/late December. If you count backwards from mid November, any plant that is planted by Oct 1, has six full weeks minimum to settle in, and often much longer.

And fall planting is like having an entire season jump on next year.

I've planted lots of perennials in the Fall and they did fine. Put them in as soon as the weather starts to cool a little and make sure they get lots of water. They should have time to get well established before the ground freezes.
Joann

the issue is winter heave ...

unlike trees/conifers/shrubs ... perennials need to get into the ground.. so they can GRAB HOLD .... before ground freeze ...

its really a matter of day temps versus night.. for odds of success ...

do not transplant if 100 degree days and 75 degrees nights.. just too much stress...

but if night temps are getting into the 50 or 60's .. then then can recover from whatever the day temps are ...

its all about getting some roots to grow .. to hold on.. a good blanket of mulch really helps ....

I NEVER FERTILIZE IN MY Z5 AFTER ABOUT 8/15 ... we do NOT want lush vegetative ... GREEN .. growth late in fall.. we want the plant to harden off properly .. so dont get some bright idea that you can HELP your transplants with a heavy dose of fertilizer ...

ken

No worries, I never use fertilizer on a newly planted plant. I only use root stimulater. I'll usually fertilize the next season. Then monitor from there.

Well the next 7 days are going to be in the low to upper 70s with lows in the upper 50s...time to get cracking.

I have daylilies and dianthus to plant.

I'm in northern Michigan, and regularly plant perennials in the fall. I tend to avoid fall planting for things in small pots with small root systems, and things that are questionable about whether they'll make it through winter (guara, agastache (the red/pink ones), etc). But I'll even plant those things reputed to frost heave such as heuchera without problems. Using those criteria, I rarely lose anything fall planted... You definitely don;t need to worry about daylilies!

Beth
Z5 Michigan

I buy more in spring because more is available but I plant more in fall because they get a winter and spring of rain before our short dry summer.

If planting potted perennials in the fall, make sure that the plants are not "pot-bound" with a solid mass of roots filling up the pot and encircling the rootball. Break up and separate the main roots with your fingers before you plant and don't be afraid to even break off or cut away some of the congested roots. The roots need to stretch out and anchor themselves in their newly planted site, or the plant will heave badly in the winter and/or following spring. Potted plants grown specifically to be sold in the fall and divisions from your own garden will not have this problem.

Sounds like its a go.

Looks like I'm dividiing some exisiting daylilies, which is no problem at all.

I'm then planting some Dianthus Rosish ones from a #1 (1 gal) cnt. I'll be sure to check the roots.

BTW, anyway have good results with the Dianthus rosish one, or Dianthus in general?