I always find that my portulaca (moss rose) does better in the ground than in pots, but you might be lucky. I plant mine in all kinds of soil from poor soil to my beds that have been enhanced and I give them Miracle Grow fertilizer every few weeks and they bloom like crazy for me. I do pick off the flowers once they have bloomed (the ones I can keep up with) so they will branch out. I love my portulaca and mine are just now beginning to flower--I saw my first yellow and my first double orange today . . . and they all came up from seeds by themselves. I sprinkled the seeds in the fall right in the ground and I have so many I don't even know what to do with them all!!! :) Donna

Do you have lots of drainage holes in that barrel? Sounds like they are drowning to me.
Portulaca is a succulent, likes it dry dry!
Linda C

And heat. I noticed you're in zone 5. Do they have full sun? Im in zone 8 and my moss rose are in all day sun. It's been 105 degrees + for a few weeks and my moss rose are going crazy with tons of flowers! If its not hot in your area, slide a few stones under the foliage to reflect the heat back onto them. They'll like that.

I planted in the ground last year from seed and I remember clipping the first blooms off and getting better branched plants with a whole lot of flowers! This years are all self-sown!!
BTW just because a plant is a succulent doesn't mean it won't want some water...succulents will take plenty of water during active growth as long as it drains freely. I am constantly having to water my Jade and other succulents I put out for the spring/summer in containers....especially in this hot dry summer climate with a 17" average annual precip.

Vera