My #1 disappointment was the dwarf/alpine Goldenrod (Solidago cutleri) I bought a couple years ago from a local plant sale. Oh horrors, it is such a washed out golden color. And here I have slowly started to change my opinion the color gold in the garden and was starting to appreciate it, LOL. Maybe the problem is it blooms in the spring and is incongruous with the pastel and jewel shades of spring.

Also a tad let down by my new Helenium 'Tie Dye'. I still really like it (I'm a Helenium lover), but a little disappointed that there are ZERO "purple-pink shades" to be seen in the flower. I mean none. I wasn't expecting to be blown away with violet purple and bubblegum pink colors, just a slight shading. Yet again the sellers exaggerate! Lol. Honestly I don't see a whole lot of difference between 'Tie Dye' and 'Loysder Wieck'.

So what are your great disappointments in plants this year?
CMK

Ideas from anyone would be appreciated. Please do not bash a newbie gardener for planting the wrong plant in the wrong place! I know I will be taking them out but should I move them or is the browning thing what they do ? In which case I will not bother to transplant them.

I had purchased some orange phlox that wound up being a very dark pink so I made lemonade with the incorrect plants and moved them into the bed for more pop. Here's a pic with both plants and you can see the difference with the pop of color from the phlox. Still sad about the coneflower.

Also a dud is Amsonia hubrichtii - A big weed that never turns yellow like people claimed it would.

Lavender 'Hidecote'. A friend gave me two starts, but with the torrential rain we've been having just about every week, they're not looking too good. I'm hoping they make it through the summer.

Tagetes patula ‘Sparky - I must be the only person in the universe to plant three marigold plants and have no flowers. Not even a single bud.

Oenothera fruticosa (primrose) - another plant that has done absolutely nothing since being planted.

Update: I stand corrected. I looked back over my old plant orders and I do not have amsonia hubrichtii. I have Amsonia Tabernaemontana. I ordered 2 online in 2011 and both are growing very well. I guess I misordered though this one is supposed to turn yellowish in fall but never has for me.

Also, I usually think of bad plants in terms of what I didn't do right. Maybe I didn't do research and find out the best cultivar. Maybe I didn't plant it in the right place. Maybe it needs more or less humidity or moisture, or maybe the drainage, or pH is wrong. I expect some plants to be more exacting in their needs, but they all have conditions in which they do their best. I haven't planted any tall Phlox because all the tall Phlox around here I see is prone to yellowing and looks terrible. I wouldn't therefore say in this thread that tall Phlox is a bad plant. I just think of all those nice Phlox plants in the truck headed for western South Dakota greenhouses thinking "What did I do to deserve this?" The giant stack of Oriental lilies at the WalMart are in for a big nasty surprise as well.

Anything that is pushing the envelope for difference in size or color I expect to be more delicate. Anything grown outside of its best growing conditions will need extra help as well.

Not a perennial, but the Purple Gnome gomphrenas that I like to use as fillers were disappointing this year. Usually they get nice and bushy. This year many of them are about the same size they were in the market pack. Not sure what's up with that, although we did have a late freeze and a much wetter summer than usual so far.

TotallyConfused

Delphinium Summer Mornings. Quite pretty...then it up and disappeared.

Butterfly weed. Short blooming season for some reason this time.

Red Birds In A Tree, although I hear it is hard to grow (bought on a whim). Mine protested everywhere possible and finally died. I just liked the name (my grandmother LOVED Cardinals.."red birds"..so I thought it was cute), and also it looked like a hummer type plant.

-eclecticcottage, don't feel bad about the RBIAT- it's him not you! LOL.

It is endemic to a pretty specific area in NM, so no wonder it is tricky to grow. I've tried it several times only to find it dies out/dwindles to almost nothingness after a few years. Not sure if it is usually short lived in it's natural environs or it simply doesn't like my climate. I've always assumed the latter...
CMK

TotallyConfused

Echinacea 'Hot Summer'. If I wanted the standard pink flowers, I could have moved some of my 'Magnus' to this spot. 90% of the blooms on this plant have reverted back.

Monarda 'Raspberry Wine'.This was completely due to the horsemint catepillar destroying the blooms. I'm on a mission to combat this scourge!

Arktrees

Tried RBIAT again from seed this year. Actually did get one to live and planted it. It is about 2 little stems and it's totally lost in the garden. Blooming and very pretty if I crawl on the ground to find it!

My blue chip BB always blooms much later and for a long time. Eclectic, do you see any buds? It actually seems even later this year.

I have a dahlia that was suppose to be around 3 feet. Right now it's over 5 feet and still growing. My Rudbeckia 'Prairie Glow' seem to range in height from 3 - 5+ feet. Placement can be a bit tricky when you don't know in advance.

Kevin

I have something more, not so much disappointing as rather astonishing. What I planted last year as double orange echinacea Marmelade, this year changed to..... SINGLE YELLOW !!! (the whole clump!). And it is planted next to a yellow-leaved hosta(it was the only vacant place at the time of planting), so the flowers are nearly invisible on that background.

I pulled out various Echinacea plants --- they were awful looking and maybe infected? Mulched them.

Dianthus 'Heart Attack' is looking like sad brown crisps now. I don't recall its dying back so soon last year, but maybe the extreme heat played a roll. I won't dig them up. Hopefully they'll return.

My Just Joey rose died --- I loved that rose! I know it's kind of 'iffy' so I guess I won't search for a replacement. RIP, Joey.

I have another one that is in a shadier spot all day and its more goldish orange, so will be moved.