You can find leek plants that can be harvested in great numbers at a handful of spots:
Pelagia Farm and Battle-Born Farm in Whiterun Loreius Farm in the Pale Katla’s Farm and the Sawmill in Solitude Snow-Shod Farm in the Rift
And one early game location where you can get leeks is the starting town of Riverwood. Behind the Sleeping Giant Inn, you can find and harvest several ingredients like leeks, potatoes, cabbages, and wheat. For in-game uses, leeks are ingredient for making various soups like Cabbage Potato Soup, Tomato Soup, Vegetable Soup, and Venison Stew, which can be eaten to gain several beneficial effects – but funny enough it cannot be used to make the food item “Grilled Leeks”.
Battle-Born Farm
Battle-Born Farm has the greatest number of leek plants that can be harvested in the game. It’s located east of Whiterun, next to Chillfurrow Farm (which doesn’t have leeks, by the way). There are several fields here where you can find 18 leeks.
Loreius Farm
Our next location for farming lots of leeks is Loreius Farm, located northeast of Whiterun. It’s a decent sized farm, and this place has a total of 16 leeks that can be harvested, along with several other plants like potatoes and wheat. Just follow the road east of Whiterun to get to Loreius Farm.
Solitude Sawmill
Solitude’s Sawmill isn’t a farm, but you can harvest a total of 15 leeks here. You can also find lots of potatoes in this area, so it might be worth stocking up on both if you can use them. The sawmill is located south of Solitude near the river.
Katla’s Farm
To the south of the horse carriage in Solitude is Katla’s Farm, where 13 leeks can be harvested. There are 2 patches of fertile soil in front of the main house, and another one can be found behind the house where you can harvest several leeks.
Pelagia Farm
Just outside of Whiterun to the south, you can find Pelagia Farm. It has several fields with cabbages, potatoes, and leeks. Definitely a good score here! But if you’re looking for just leeks, then a total of 12 leek plants can be found here.
Snow-Shod Farm
If you’re in Riften and need leeks, just head to Snow-Shod Farm where you can find and harvest 10 samples of leek.
Other Sources
You can also find a few leeks on dinner tables and on plates in different houses. Innkeepers like Hulda in The Bannered Mare and vegetable merchants in towns sometimes sell leeks. Market stalls in Whiterun and Solitude have leeks and other vegetables on display, but taking them will count as theft. So it’s best to harvest them directly from farms – which does not result in a crime (somehow). Leek plants can also be cultivated in gardens and greenhouses in player-built homes with a 10-day respawn time. So if you’re looking to have a consistent supply, it might be easier to grow your own.