I’ve seen tons of methods for having grass in dioramas. The easiest options are painting the ground cover yourself, or finding a rug remnant or fabric with the right colors. Some children’s play mats have things like roads, rivers, etc already printed on them. Some people make play mats out of felt, so they can be customized completely.
Traditionally, flocking is a safe bet – and since Sylvanian Families are flocked animals, the texture fits in very well. I started out using shake flocking (found online here), and it was fairly successful; you just spread down an adhesive like double-sided tape sheets or even rubber cement, and shake the container like you’re pouring out salt. It clumps together and makes a good looking ground cover quickly.
I was fixated on having a natural-looking landscape for my dioramas, so I kept exploring materials. I decided I liked the look of preserved moss the best.
I found rolls of moss adhered to a mesh sheet, and it turns out they are super easy to work with. You can find them online here; they seem expensive, but search for a 40% or 50% off coupon at Joann Fabrics before you buy – they have coupons every week.
You can cut the moss roll with scissors and glue it down with rubber cement. The nicest thing is that you can line up two sheets and it looks nearly seamless, since the moss blends in together.
Once I have my moss in place, i take scissors and give the whole thing a haircut. I also remove pieces of straw and little twigs that held on for the ride. I like to keep it as short as possible so it looks tidy.
For tight areas or finishing an edge, you can pluck individual pieces of moss, dunk them in some rubber cement, and position them how you like. This picture shows the finished look on the left, the in-progress in the middle, and the raw edge on the right. This step can be tedious, but it allowed me to achieve a uniform look.
To finish the ground cover, I coat the entire thing in matte varnish. It makes the moss hard and crunchy, but it keeps everything in place if you need to vacuum or dust it later. I would imagine you could use Elmer’s glue mixed with some water to act as a protective coating as well, but I haven’t tested this.
For things like dirt paths, mulch in flower beds, or tiny stones, I would recommend using ballast. They’re like miniature pebbles. You can find all sizes and colors at a hobby shop for just about every purpose.