Niffelheim

You will need to build a Greenhouse for this trophy. While on the surface, you'll notice there are two structures by your Castle (on on each side):

These are what you'll use to build the secondary constructions: Chicken Coop, the Sheep Pen and the Greenhouse. You can only have two of those active at one time. It's recommended you start off with one Chicken Coop and one Sheep Pen so you can gather the Wool and Feathers needed for the earlier upgrades (Workstations and Defenses), then switch to 2 Greenhouses so you can work on this trophy.

Before you can grow vegetables, you first need some seeds. To get those, you need to go around collecting vegetables/plants on the surface. When you do, you'll get the food/item you're collecting and also have a small chance to pick up a seed for that item as well.

Once you have a seed, go into your Greenhouse (press when next to it). Scroll down to the seed you have and choose to "start" the process of growing the plant. When it's done, you can collect the goods, which will also have a small chance of dropping a seed as well.

You need to grow a total of 200 vegetables overall to unlock the trophy. Each stack will grant you a minimum of 10 pcs (that # will increase as you upgrade your Greenhouse) so you'll need to a maximum of 20 seeds to unlock this trophy. The trophy will unlock as soon as the 200th vegetable has been grown, even if you are not at your castle or even in your own land.