Looks like a striking bed, though too shallow front to back. The wavering of the border is unnecessary and unattractive. It should either be straight to match the line of the fence, or should somewhere have a major curve in it, not squiggles. No way from the photos given to tell where the major curve should be.

Your questions about plant choices might get better responses on the appropriate forums, perennials, trees, etc.

This isn't a formal border so a straight line would appear out of place. I think the perspective in the first picture makes the curves seem more intense than they really are. The lines look fine to me as they are.

The goats beard gets large & I see it covers a lot of the nearby plants as the season progresses. You can always divide & leave a half or a third of what is currently there. You want to either leave some there or replace it with something tall so you don't have a border that's all the same height. A large blue hosta like the two you mentioned would look good somewhere in the border.

Do I see Aegopodium (gout weed) by the Zebra's (love the Zebra) belly? If so, do yourself a favor & remove and destroy it immediately. I have been battling it over 10 years. I've pulled it, dug it up and sifted the soil and still can't get rid of it.

Your plant ideas seem find. My Rodgersia does require quite a bit of water so if you do go with that be careful of planting it near the roots of the tree on the other side of the fence. You might want to consider a hydrangea. Perhaps Kerria japonica would work out. I like the green stems in the winter and have been able to keep it in bounds.

I would move the Hakonechola (Japanese Forest Grass) closer to the front of the border. Do you have any Primulas? They add a nice touch of color throughout the year. I always like to move large rocks in with the plants. I like the way your border currently looks. You have a nice mixture of plants. It's always up to what makes you happy. Moving and arranging to please your tastes are a large part of the joy of gardening.

The alternative to a wiggly line isn't a straight line. Sweeping curves look better than short, shallow curves imo, too. I agree with lacyvail that a deeper bed with a less fussy edge shape would indeed look better. Beautiful healthy plants btw.

Thanks everyone, some good advice! I also agree that a deeper bed would be better, but I'm balancing bed size with active children who need space to run. When they get older I'll expand the beds. In the meantime, you all make some good points, and thank you, floral_uk for the compliment on the plants!

aardvark, I like your suggestion of hydrangea and to give some colour spots with primula. I don't have any - I tried some dormant roots a couple years back but they didn't grow and I haven't acquired any since. I'll have to look for some this year perhaps. As for the tree on the other side of the fence and the goutweed - tell me about it! Both originate from my neighbour's side and both are out of control. The tree(s) are actually just runaway seedlings dropped everywhere by their horrible Manitoba maple that's rotting and about to fall. Those darned seedlings can reach 15 feet in a year I swear! The gout weed is also volunteer from their side - I've been battling it for several years now but without breaking into their yard there's not much I can do but keep it back against the fence. They even ehave a lovely little Star Magnolia getting choked out by out-of-control juniper. It's the saddest thing - I asked once about rescuing it but they always say they're going to clean up their yard. Sigh. What can you do though? Nice enough people, just not gardeners!