Hello!
While working on the Edhellond map a few months ago i found a method for creating gardens quickly with voxelsniper! Here it is (mostly copied from the old forms)
Part 1: brushes
The brush we are using is the overlay brush.
The Overlay Brush will “spray-paint” the top most blocks in its area to the blocks set by your “/v” command. This can be used to easily clean up any exposed materials once you are done with the erosion brush, or to create new fill material two links two pieces of landscape together.
The exact command we will use is /b overlay d-1
.
Part 2: The voxel
This one is both very modifiable and can be difficult.
what we need to do is tell voxelsniper what percentage of certain blocks we want in our terrain. The format is fairly simple.
However, it gets very long if you want lots of different flowers
. Each section is X%(ID), For example, 20% of placed blocks being grass would be 20%31:1,
The comma at the end is needed to separate 2 different blocks, but not the end of the command.
Step 1: Air
This will affect how dense your terrain is. I mostly use 30% for dense gardens, and 70% for large fields.
Step 2: Grass and Ferns
This is the backbone of your garden. I tend to use about 20-30% grass, and 5% ferns. this added to the command looks like this: 
Step 3: Flowers!
This is the longest part of the full command. What you do is you add what percentage of the flower you want, then add the ID of the flower you want. For example:
Congratulations! you now have a command to make gardens and grass! Make sure to use gunpowder when using this command, because otherwise, it won’t work properly.
My commands:
Here are a few of my commands:
Red and white theme:
/v 30%air,20%31:1,5%31:2,5%38,5%38:4,5%38:3,5%175:3,5%175:4
Blue, white, and pink theme:
/v 30%air,20%31:1,5%31:2,5%38:6,5%38:8,5%38:1,5%38:3,5%175:5,5%175:1