Preheat the oven to 350°F (175°C) and line the muffin tin with 12 paper liners.
In a medium bowl whisk together flour, baking powder, baking soda, and salt, then set aside.
In a large bowl beat the softened butter and granulated sugar with a mixer on medium speed until light and fluffy, about 2–3 minutes.
Add the eggs one at a time, beating well after each addition, then mix in the vanilla extract.
In a small bowl whisk together the milk and sour cream until smooth.
Add one-third of the dry ingredients to the butter mixture and mix on low just until combined.
Add half of the milk mixture and mix on low, then repeat alternating dry ingredients and milk mixture, ending with dry ingredients, mixing only until just combined.
Divide the batter evenly among the 12 cupcake liners, filling each about two-thirds full.
Bake the cupcakes for 16–18 minutes or until a toothpick inserted in the center comes out clean.
Remove the pan from the oven and let the cupcakes cool in the tin for 5 minutes.
Transfer the cupcakes to a wire rack and cool completely for at least 25 minutes before frosting.
To make the buttercream, beat the softened butter in a large bowl on medium-high speed until creamy and pale, about 2 minutes.
Gradually add the powdered sugar, 1/2 cup at a time, mixing on low until incorporated, then increasing to medium speed until smooth.
Add vanilla extract, salt, and 1 tablespoon of heavy cream or milk, then beat on medium-high until fluffy, adding more cream as needed for a pipeable consistency.
Divide the frosting into 4–5 small bowls to create different succulent colors.
Tint each portion of frosting with gel food coloring to get various greens and a few accent colors like pink, purple, and yellow, mixing well.
Fit piping bags with a leaf tip, small round tip, and small star tip, then fill each bag with a different color frosting.
If desired, spread a thin layer of plain frosting on top of each cooled cupcake with an offset spatula to create a base.
Pipe small rosettes, stars, and rounded mounds in clusters to resemble different succulent shapes on each cupcake.
Use the leaf tip to add small pointed leaves around the clusters to complete the succulent look.
Chill the decorated cupcakes in the refrigerator for 15–20 minutes to help the frosting set before serving.