I'm just learning about rhubarb this year.
So far, the little roots I bought (pencil to little finger diameter, maybe 5 inches long on average) have produced what I consider huge plants, given the root size; 18 inches across or so. We haven't hit hot weather though, just up to 27 to 29 C on occasion, mostly lower than that by 10 or more degrees (we had a freeze, 0 degrees C, at night 3 days ago).
I adjusted our sandy loam soil with additional sand to make a loamy sand, then mixed in lots of compost and about a tablespoon of granular 13-13-13 fertilizer to a 3 gallon nursery pot (temporary measure until I finish making a raised bed for rhubarb). I top dress with another teaspoon of fertilizer occasionally, before a rain. I water about every other day unless it has rained recently. So far, no bolting yet.