If you actually like the plants you already have, I would start with an inventory/list of the varieties, colors, bloom seasons, and have this as a list of available plants to select from when/if you consult with a landscape designer to help you with a new layout. If you know that many, or most already are at a point that they need dividing/thinning out to keep them looking good, why not do so and maybe park them somewhere else in the yard as a temporary holding bed.

Not having any photos to look at, it is hard to know whether a designer would be tempted to want to start fresh, or if the existing layout lends itself to working with what you already have. Moving perennials is work, but certainly easier to do than moving trees and shrubs. You might find that your best/favorite plants could be so divided to form large masses that really make your new garden design have that 'Wow" factor, with just some supplemental new purchases and infill. You might also find that it makes sense to move some plants so that their cultural conditions are met; maybe some things are in too much shade, too much sun, too wet, too dry, etc, or that the color combinations don't work well, or intended color combinations don't work because the bloom periods don't coincide. If you have lived with the garden for a whole season(spring thru fall), you may have some good ideas yourself as to what is working or not...

You also might consider getting over to the Ball Flora Demonstration Gardens in West Chicago to get ideas, I just attended a talk by one of their hybridizers, and saw a few slides of the gardens, they do look worth checking out...

I'm assuming you are doing this yourself, rather than hiring a designer? If so, make a scale drawing and play with changes to it. If the current layout isn't working, plan a new one, leaving space for perennial beds without selecting plants as you add new elements, like patio, walks, screening planting or whatever you need.

Plan beds for perennials in locations that have the right conditions for the plants you want to grow. Once you have the layout down, you can start thinking what you want to plant in them, and start redistributing some of your existing plants into them.

This is a good time to compost the non-performers, divide and increase your favorites, and as Bahia suggested, mass them together in drifts for more impact, rather than dotted around, if that's what you have now.

Try not to be guided too much by the plants you already have. You don't want them to limit your design if they are not the best choices. If there are leftovers, put them in a holding bed or cutting garden in an out of the way spot, or share them with friends.

This is probably how a designer would approach it.

Redesigning perennial borders is a lot of work if they are large. Even with a plan in hand, you'll have to dig up sections, unless you have help or lots of time and can do it all at once, and replant them, moving the extras to pots or holding beds.

I walk around the garden with a clipboard and make notes about what should go, what should be divided, which plants I'd like more of, what needs moving forward or back in the borders, etc. I also make notes that "section 4 is too quiet in August" or "some of plant X would look good next to shrub Y" or "the pink whatsit in section 1 isn't working". I refer to these notes when I have the time to make changes. I'd never remember in May what I noted in July or August of the previous year without writing it down.

Thanks for your responses, bahia and saypoint. I am looking to hire someone, but I think your advice about making lists and having a good idea about what I want where is important. I've got photos of most in bloom and have taken measurements and notes this bloom season ... the planting plan, though, at least right now, overwhelms me. This is probably one of those projects that I just have to keep plugging away at in order for it to fall in place. Thanks!

You mention having photos of plants in bloom. Keep in mind that, especially with perennials, the bloom time is relatively short for each plant. Think about foliage color and form, and texture, when thinking about plant placement. Look at your current plantings and note whether they have coarse or fine foliage, and what the flower shapes are. Are the plants dense mounds, or airy and almost transparent? Daisy shapes or bells or umbels or spikes? Is there a good mix of these qualities, or are there too many daisies near each other that bloom at the same time?

I have plans of my borders showing the location of every plant, not to scale, but just to have a record of what is where. I occasionally walk around with the plans for each section and adjust the drawing to reflect increased clump size, deceased or discarded plants, new additions, etc.

Then again, sometimes you just have to walk around with someting on the end of a shovel.

Draw a plan of "what is" first.

Then look at it to see "what dies", "what moves" and "what stays"

Do what you can to minimize the shuffling, but it an iris bed is smack where you want a BBQ ... move the iris.

I'd venture to say that a good percentage, if not most, landscape designs address an existing garden rather than the proverbial blank slate. Certainly most of mine do. Relocation of existing plants is almost always a factor. There is much to be gained, not the least of which is maturity and size, by re-using existing plantings. Lazygardens' outline is essentially what I follow - the base map will indicate the existing location, subsequent schematics will indicate relocation or removal. It is not all that difficult to move many plants - large trees or shrubs being the primary exception - and most will adjust to the move without problems if timing is correct and proper care is taken.

More good ideas ... thanks! I don't know why I'm so stymied by this project. I've got several smaller beds that I've planted with great results. It's this one area I just can't seem to coordinate. It's a large l-shape along my fence ... back of my yard, to a deep corner on the right, then along the fence again on the right. I seem to do better with "freeform" areas.