When there are gaps I want to fill in my gardens, the answer is not more plants. Since none of my plants ever touch, if I fill a space with a new plant the other mature ones around it shrink so they won't mingle together or blend.
The answer to filling spaces and tying forms together, instead, is rocks.
When I moved the Leilani coneflowers from the dining room window garden where they were in too much shade, I filled the empty spot with some rocks flanking the peacock. I'd like it better if the stones weren't white but that's what I had.
When I took out the tiny struggling nepeta at the front of the kitchen courtyard, I put in a small curve of rocks. I added three in the gap in front of the little serviceberry twig. No plant in this garden will touch another beside it, even after years and maturity and all my care. They shrink to nothing if another thing grows too near. So rocks have to do the job.
In front of the fence, in the middle where the eye goes when sitting on the patio, I put a long flat stone, another hidden partly behind it and then arranged a rock and some pebbles under the birdbath. Placed "just so" my intent was a natural looking scattering. The randomness fills the empty foreground here and transitions to the flagstones in front.
The key to artful scattering of rocks is to vary the sizes and set them irregularly as if they were there naturally. I could do more with different sizes of pebbles and river rocks together in front of the alliums in this little vignette.
In my friend Andrea's garden she has random rocks all over, and because her garden is full and lush (her plants happily touch each other) they appear hidden, tucked in under foliage and peeking out around flowers, making a natural contrast of loose plants and structured forms.
I need to do more of that in my garden and use more varied shapes and sizes, placing them in gaps wherever.
Here's an example of a design similar to my circle garden, but irregular flagstones, river rocks, small stones and pebbles are mixed in around the curve, tucked among plants in places. It adds definition without being too formally rigid.
Here's another example of randomly placed rocks filling gaps and defining edges. I like the way brown river stones are mixed with some white pebbles.
I don't want a classic rock garden and I don't want a stiff stone border. I just want random river rocks, pebbles, irregular stones and natural forms scattered around my plants to rest the eye, fill a gap and add some structure.