Choosing to plant Iceroot or Shaderoot carrots changes a legendary you can catch. This Pokemon Sword & Shield Crown Tundra Iceroot Carrots Or Shaderoot Carrots guide breaks down the details so you can decide whether you want to plant in the snowy fields or the fields by the graves.
There are a lot of Legendary Pokemon in the Crown Tundra DLC. One of the new Pokemon is Calyrex. There are two options here, allowing you to make a decision on what type of legendary Pokemon Calyrex becomes. Where you decide to plant your Carrot Seeds determines which carrot will grow, and that in turn decided which steed you will attract to Calyrex.
If You Choose Iceroot Carrots
If you choose to plant your Carrot Seeds in the fields covered with snow, you will eventually turn Calyrex into a Psychic/Ice type Pokemon. There’s still a few story missions to complete after you plant your seeds but before long, this is the Pokemon you will be able to catch.
If You Choose Shaderoot Carrots
If you plant the Carrot Seeds in the fields by the graves, they will become Shaderoot Carrots. If you choose these carrots you will make Calyrex a Psychic/Ghost type Pokemon instead. As with most choices in Pokemon, both are perfectly viable. They are strong within their types, it just depends on which you would prefer to add.
There is no going back from this decisions. You can only catch one of the two so if you plant the Iceroot Carrots, you will not be able to get the Psychic/Ghost version of Calyrex without trading.