To summon the landlord, you need to offer 3 type of food. I'm not sure about this 'coz i've not play the mod for a several month, so i might be wrong but i'm pretty sure you can see the dishes to be offered in the "Myth Book", the book you can get by set the book on fire with torch or fire. It should be 1) Wine Gourd, 2) Peach 3) Meat? nah that's i'm not quite sure. The Landlord will help you to nurture your plant as long as the dishes still on the offering table. Hope it help.

You can give the landlord a vegetable meal, a meat meal and a drink like wine. It has to be one of each to summon him.