Start with a wooden base. My base is a stained/finished wooden plaque that I bought at Michael’s Crafts. The landscape is made from a base of styrofoam, then
covered in a baking soda/cornstarch clay. Here’s the recipe:
1 cup baking soda
1/2 cup corn starch
3/4 cup water
Mix baking soda and corn starch in a non-stick pan. Stir in water over medium heat and stir continuously until mixture becomes the consistency of mashed potatoes. About 3-5 minutes. Remove immediately from heat an place into airtight container. After ten minutes (or when cooled off a bit) knead dough until smooth. (Overcooking the dough will make it crumbly.) Clay will dry overnight. Some shrinking will occur and cracks will occur as well, so keep a little extra clay to fill those in.
Cover styrofoam and wood with clay, sculpt hills, valleys, etc. and let dry.
Next, I will need to prime the landscape before I begin painting/gardening.