This is a good idea to use the first scatter to get the clusters and then for each cluster perform another scatter to get the plants. You can create a surface around each cluster point and then perform the next scatter on that.
The following code creates 3 cluster points and, for each cluster, inserts a 10x10m quad surface on which a subsequent scatter is performed to get 6 points per cluster.
Lot -->
scatter(surface, 3, uniform) { Cluster }
Cluster -->
s(10,0,10)
center(xz)
primitiveQuad
scatter(surface, 6, gaussian) { Point }