Absolutely lovely. Just a gentle reminder that under the ground there are all the roots of those trees, competing with your flowering plants. The root systems of the trees extend out beyond the reach of the branches, and oaks have roots quite near the surface. So, if you find later in the season that your plants start struggling somewhat, that is the reason. The water, fertilizer and any soil amendments you used when planting the flowers will 'attract' roots of the trees.
I have huge oaks all around the house, and struggled with this for years. Now I plant my favorite shade loving plants in large pots, and move them around as they bloom, for best effect. You can also sink pots into the ground to give your plants a head start, but eventually the trees will get their roots into the pots, too!
Some plants compete well with oak tree roots, and others simply give up. Heliconias, caladiums and gingers seem to do fine in the ground under my oaks, but things with fine roots like cane begonias simply can't compete. Bromeliads are excellent under oaks, as they don't really have much of a root system, and take most of their nutrients from the air. Hummingbirds like several kinds of bromeliad flowers, too.
Long story short, if some of your butterfly plants start to peter out, I'd lift them and put them in pots to keep them going.
