| Hello from an amaranthus junkie, I think your amaranthus will be fine planted by the roots. Amaranthus are very easy to grow and very hardy but Ive found they self seed tremendously. I would suggest not putting them anywhere that you didnt want a bunch the following year. I was very interested to learn amaranthus leaves are edible and the seed can be used as a grain although it is said to be much grittier than other grains.
I personally love the different varieties of foilage. Enjoy and happy gardening. Lookingglassgardengirl | 
