My first thought is that you may be watering too well. You want your new perennials to develop strong root systems, and if all the water is near the surface, the roots will not go as deep as they should. Also, most of the flowers you mentioned prefer good drainage, so make sure they don't have "wet feet". I would remove any buds that have formed, so the plants put their energy into foliage and roots.

You may have rotted root systems or just struggling ones. Only cut off what is clearly dead. You want as much photosynthesis as possible so you need as much foliage as possible.

As far as watering this year, after all that rain we had, I have yet to water anything but a few pots. 5 days of no water is fine under these conditions. Where I am (northern MA) I am just starting to think some beds may need watering for the first time.

What kind of soil are they planted in? Is it rich loam or lean and mean? Is it very well drained? Before you water, check the soil and see if it needs it.

My mom (a master gardener) recommends the 3-2-1 watering schedule for new perennials. It has worked well for me this year.

The first week, water 3x a week.

The second week, water 2x a week.

Once a week thereafter (unless you get a good inch of rain).

I put in several perennials early this spring and watered them pretty close to as described above. Now I'm not watering them at all. I've been putting in new stuff all summer, and as long as I put about two weeks into checking it frequently and really baby it those first few days, everything has made it! We've had more rain this spring/summer than usual, so that has helped.

Here in New Jersey we had a month of rain. It seemed that after it stopped raining the established plants needed to adjust to sunlight (finally!) and getting less water. That adjustment may have been to much for the new small plants.

You mentioned your sprinkler system failed - So your small plants went from to much water to none. The bluestone plants are quite small with only a few inches of roots - . I would cut back to a few stems with leaves, and water carefully (not to much or to little), but I don't think you should use any fertilizer at this time.

How much to water depends very much on the kind of soil you have. Sharp draining soil, which I suspect you have in New Hampshire needs to be watered more often that heavy soil.
The phlox just dies that....it's a fungus, don't worry it won't kill the plant just make it ugly. Next year you may need to spray with a fungicide to keep that from happening again.
Most of the symptoms you describe sound like those that happen with plants which are dry. Yes, you want plabnts to develop a strong root system....but new plants have most of their roots near the top of the soil and you need to supply water there for the first year. And, some plants always have shallow roots and never send roots down deep.
Other concerns, are they in lots of sun? and did you apply a chemical fertilizer? Fertilizer can cause some of the symptoms you describe.
You say you have mulched? With what? Hopefully not with rocks and plastic.
Since youo say you are a new gardener, I suggest that you dig into the soil to test for moisture every couple of days until you get the hang of how much water your garden needs. Just move a little mulch and dig down about 2 inches.
Good luck!
Linda c

I have been ordering from Bluestone for about 6 years. My experience is that if I can get them planted early in the season they do ok. But not infrequently they get overtaken by their established companions and I lose track of them- forget to water, they get too much shade from the bigger plants.
The most serious problem is created by my not getting them in ground while they get pot bound in their little pots or six packs.This happens especially when I get too busy at work or with family mid-spring and garden chores call and I forget the potted babies.

This year I changed my ways somewhat. I bought a big bag of miricle gro potting soil, which people on the winter sowing and propogation forum seem to like and repotted every thing- 25 small ones- into larger pots. I wasn't careful about drainage: just threw in a handful of soil, put plant in, more soil, firm and water. Or a big shallow container of water and let the water wick up through the drainage hole.

After a while I just dumped the potting soil on the table and scooped.

I was just amazed at how fast those babies grew to fill up pots 2-3 x time the original size. They are big enough to compete in the garden and big enough to stay in the pots or to pot up again to plant in fall.

I know many people feel they don't have time to pot on, but given the choice for me is do or die, the hour I spent potting has saved me a lot of money in plant losses.

I'm not efficient, I'm a plant killer by procrastination.

idabean - I did the same thing this year and potted up my bluestone purchases (I bought them during the clearance sale - so it was late in the season). It seems I can pamper them better in pots and they doubled in size quickly. They get lost or forgotten if I plant the tiny plants in the garden.

Keep up the careful watering.

Thanks for the feedback to all.

pegnj - I think you're right, the lack of water (oddly enough, after all that rain) was the problem. A week on from the OP and I can see improvement in most plants. Although sadly the agastache purple pygmy might be done for...

Lindac - well drained soil, for sure, but I did amend the new beds with 3" of good heavy compost before planting to mitigate that problem. Plants are in full sun; the mulch is shredded bark mulch. I did do a little fertilizer, those osmocote time release pellets...is that a bad idea?

idabean - that sounds like a great idea. I have killed numerous small plants over the years because of transplantation procrastination. I've even had plants root into the ground in their staging area through those little holes in the bottom of the plastic pots! But, this year I got a little lucky because with all the cool wet weather the plants didn't have a chance to really get rootbound.