Despite the heat you are having, your garden looks really beautiful. RC looks like he enjoys his time in your garden.
I loved seeing your garden on video. I have never grown Calla lilies so I can't help you there, but I immediately recognized the Silver Streak perennial as a type of coral bell. I love coral bells but I have not had good luck with them, which is one of my great disappointments in the garden. Last year we visited the Marsh-Billings-Rockefeller National Historic Park. Coral Bells were growing in the garden there. They had gone wild, even growing out of cracks in the stone stairways and rock walls. I don't know what I'm doing wrong, but mine didn't even survive one winter in my garden.
I agree with you about those roses you are drying. They are very pretty and would like nice on a wreath. Cha Cha is a very lucky rabbit to have such elegant treats!
You asked for some ideas for your new border that are no cost. My first thought is to try propagating new plants from the ones you already have.
I have been able to root roses in water, though they have not survived the harsh Maine winter. I think I need to bring them indoors for their first winter, so I'm trying again. But yours might do very well with the Portland winters. On Pinterest, I've seen pictures of roses rooted in a potato! I've never tried it but it might be fun to see if it works.
You could also divide your hostas. Each small part can become a new plant. The mint and lemon balm could be divided up and used to fill in spaces. I have been rooting basil this year from cuttings. I started by buying a pot of basil from the grocery store, pinching them back and rooting the cuttings. They root so quickly, you can have new plants in no time.
I have been experimenting with propagating my own plants. I find forsythia is one of the easiest. I can just pop a stem into water and it will root. I have read that other shrubs can be rooted either in water or with rooting hormone. I have tried hydrangeas and spirea with no luck, but other people have done it. If you know any friends or neighbors with shrubs, you could ask for cuttings and give it a try.
Some wild flowers, like daisies, can look nice mixed in with cultivated plants for a cottage garden look. This is the time of year to look for wild flower seeds on walks. Seeds are also on sale at various stores right now, such as Dollar Tree. I found seed packets for 10 cents each.
Do you have any other plants that could be divided, rooted or grown from seed?
Well, that's all for now. I hope your heat wave breaks soon.