When you say you put a couple cups on a container I assume you mean you mixed with water at the rate on the package and then applied a couple cups of the dilute solution.

If that is the case I really doubt that has caused them to decline.

If, OTOH, you applied a couple cups of the dry powder to the containers then they are toast ;-)

Yeah, it was mixed up per the gallon instructions. Container is about...um, I'd say ~2.5 gallon pot. I didn't think fert would cause decline, though, but they just all look like someone stepped on them. All of what WAS in bloom (the daisies & verbena) are now shriveled, but still upright, and the bacopa blooms have turned brown. The foliage is still green, but all the blooms are toast.

Sounds odd, but I doubt the fert is the cause. Unfortunately I don't have the first clue as to what would cause the blooms on different plants to all go bad while the foliage appears healthy.

I mean, it could, kind of sort of, hypothetically and theoretically be attributable to excess nitrogen, but I doubt it.

Sorry I can't offer more help, perhaps someone else will come along soon with some wisdom.

Hmmmm. IF you mixed your fertilizer according to label directions or less, damage would not result....even though your plants did not need the extra boost with the slow release you incorporated.

Did your potting medium ALSO have fertilizer mixed in? Many of those commercial brands do, these days. Out of curiosity, I looked to see what my local big box store carried and I was hard pressed to find something without added fertilizer, water absorbing crystals, etc.

Nope, nothing in it. This was the mix that the 'container workshop people' gave me to use when I did up the container a month ago. It was soil-less mix (you may recall my thread on this subject) that was very much like dehydrated potatoes...there was nothing in the mix, which they told me...which was why they put in the osmocote pellets.

I'd never used this mix before, so figured it was about time for another 'feeding' of it (course, I probably should have looked up the Osmocote first to see what the timeframe was on that).

Anyway, I put the fert on day-'fore-yesterday, and noticed the damage last night as I was watering another section. Maybe...hopefully...it will recover in the next several days.

I wouldn't be whining so much except for the fact that this was the first 'real' container I'd ever made, and it came out AWESOME (IMHO)...with the buttery yellow agyranthemum as the centerpiece, the white bacopa trailing over the sides, and the medium purple of the verbena starting to really fill in the rest of the arrangement. The container is a resin 'antiqued' looking thing that is grayish-greenish with a tuskany-type look to it (grapes/flowers, etc molded into it), which really compliments the plants, and the whole thing sits on a small weathered wooden chair flanked by a basket of pink petunias at the foot of the chair.
Yeah, ok, I'm bragging a little on this one, but haven't you ever made a container that just made you go: "Wow...I did GOOD!" (as opposed to just "yeah, this is a nice one...")

So that's my story. I'll come back with a pic hopefully when it recovers.

It DOES sound gorgeous! Don't give up on it! Keep the bad parts clipped out. Say, this dehydrated potato looking (lol) mix does drain quickly, right? I do recall your posting but can't remember what those people told you to use.