I'm not an expert, but started growing rhubarb from a friend's starts a few years ago in fall.

Go back & plant the 3 parts separately (3-4' apart) because they're greedy for space, moisture, & nutrients. Rabbit manure + coffee grounds topped with straw helps ours keep moist. Also check to make sure the crown is at proper depth. Try burying an upside down 2 liter bottle (bottom off) about 1' away from the crown to direct the flow of water from hose or bucket. All that compost flows away sometimes ... & if you have watering helpers they might not realize what they've done...

Depending on your climate you might want to put them in afternoon light shade. Mine flop a bit in the heat of the day, but perk back up in the cool evening.

Yours might be flopping because the roots aren't working yet to pump enough water in them... happened to ours when we had a sudden temp spike this spring & we were out of town. Stalks weren't even that fat on some, but I pulled them because they didn't perk back up.

You could pull the fat stalks, but no more than 1/2 of the stalks so plant will have something to produce food to grow. By the way cutting stalks causes rot, just twist & pull.

Each time I pull that spot on the crown grows a new stalk. That's why picking is limited until plant is established. Too much energy produced making stalks instead of roots.

Baby them a bit & they will make it!

Thanks. It looks like it took. We harvested some of the stalks and there are some small stalks perking up and growing. I've got it planted in a well formed by berming up soil and I buried it in compost.