These instructions can be used in several small scales, as you're working from an in-scale sketch rather than fixed measurements. Please visit my garden center for an overview of all my free flower DIYs and other files about making flowers.
For 1:120 and N (1:160) scale, you can use the supplies listed below. In 1:48 and H0 (1:87), I suggest you use fine blue foam instead of Nu-foam. The green foam listed should work in H0, but for 1:48 you can use coarser foam or punched leaves. The flower supplies page has more information on supplies you can use.
If you'll use Nu-foam, tint a small quantity of glue to match the foam.
Apply (tinted) glue to the flowerhead area...
... roll it in Nu-foam...
... then roll it lightly between your fingers.
Put a pinch of green foam on a sheet of paper and separate the bits from each other.
Apply glue to the area where the leaves will go, and apply bits of foam one by one. If they're too large, tear them into smaller bits.
For a fuller effect using the same foam (e.g. in H0), apply foam by rolling the stem in it.
Let your flowers dry thoroughly before planting them. For planting hints, please see the Basic flowers page.
For a grouping of the same kind of plants, you can glue greenery to the ground instead, as tall as the leaves on the plants should go. Trim the flower stems at ground level, dip in glue and stick them in the greenery.