Rhizomes are usually dug when they're dormant and kept refrigerated to help hold them back. If that's what you're planting, as soon as you can work the soil is a good time to get them in the ground. Once it begins to warm up, they'll start poking. In your first year you should let everything grow as the more foliage it can produce, the more food it can produce to help build a strong root system and crown. Once they're established they'll generally produce many more shoots than you'll need so folks thin them out.