First of all we like plants or are employed by/through them to some degree.. so welcome brother!! (Not that I'm addicted either...;)

What are the goals you have for your landscape? Obviously your plants and enjoyment of them are key. Maybe some like WoodyO could give you more advice than me about this, but what else is important to you in the garden as far as uses and views?

No, I'm not addicted to plants. Not at all. And the Japanese Maples at work NEVER follow me home...nope. They do NOT.
Actually, I'm not collecting plants and shrubs and Japanese Maples. I'm...using my yard as a TEST garden. A proving ground. That's it. ;^)

I've found that hardscape can be a very unifying element. The rock walls I've inherited (and built) help give my hodgepodge some structure.

I agree with mjsee - hardscape can be a great unifier. Whether it's a consistent walkway type or rock walls or even just some nice large rocks.

Or, you can add in garden art or birding accoutrements. But that would be another thing not to collect.

Objectify your garden; take some photos of it.

You know how you feel okay about yourself and your appearance on a day-to-day basis, but then you see a new photo of yourself and think "Omigod who IS that old/sloppy/overweight/skinny/overdressed person in need of a decent hair cut and some more flattering clothes?!!? Right! So do the same thing with your garden, and it will change the way you look at it.

Take photos of the usual views you normally see from your street or sidewalk, from the front door, from the back door or the outdoor dining area. Suddenly in the photos you'll notice things, like junky, mismatched pots, or the repetitive nature of your collecting, or the jumble of overgrown plants, or the lack of adequate paths.

And if you're not overly sensitive to criticism, post them here and ask for feedback!

FWIW, I think that a key element that collector garden tends to lack is repetition. The observation about hardscape providing unity I think is tied to this. Don't just have one of everything -- repeat plants or at least types of plants in clumps.

Topography and rock groupings working together is a very strong unifying combination that even the craziest plant collector will have a hard time overcoming.

Any opinions on groundcover as a unifier? Or color?

To what extent do they work or not work?

Being in space-starved urban CA, and add in hardscape that cuts up a 5600 sq. ft. property into 15 separate garden beds, means I don't have the luxury of the whole 'plant in threes' philosophy. There simply isn't enough room.

I've found that the eye needs contrast. People think in terms of flower color, but I've found foliage is much more effective in unifying disparate plants (I agree, BTW, that hardscape can unify, although I have a lot of different-material hardscape). A chartreuse Lavatera olba, for example, is echoed by the yellow daisy-like flowers of a Euryops a few feet away. The silvery grey Santolina breaks up the too-similar greens of agapanthus and daylilies, and is echoed a little ways away by an even more silvery Artemisia 'Powis Castle'.

One of the biggest issues with designing interesting beds, instead of hodge-podges, is layering heights. Too many people fail to have their highest layer elements relate properly to the ground-level elements. That's why Catkim's suggestion of photos is really valuable; it makes you look at what you've got right now. It's up to you to train your eye to see what's missing - not just another interesting plant, but a better plant well-suited for that particular site that will unify the 'look' into an interesting whole.

I'm thinking that we are talking about someone who is acquiring plants without the option of planning compositions ahead of time - like a landscaper who winds up with "used plants" or "leftovers" who is looking to pre-build unity or at least have the ability to build unity on the fly. Is that correct?

Catkim's photo suggestion is a good one. I would add to it by suggesting you either take black and white ones or print color ones in B&W. Without the distraction of color, what you see is quite different.

The two things I've found most helpful in my journey through improving the garden are
- shaping the space that the garden beds are in rather than just shaping the garden bed - the negative space issue (a 'lightbulb'moment for me) and
- using a limited palette of colors - either overall or in each major area. 'Monochrome' is not boring; it can be quite striking (and is not usually literally monochrome). It also has the benefit of keeping random plant buying in check because you get to the point where if the color doesn't fit anywhere, you don't buy it. Mind you, on the other hand, you have another thing to seek out - i.e. just the right color to fit wherever... :-)

There are a variety of other things I do to try to make things flow well. I don't have a lot of hardscape but I do have lots of paths which are essential to the garden on many levels. Because half my space is in sun and half quite shady, finding and using plants that perform well in both conditions helps connect the two spaces.

I have lots and lots ofplants, particularly flowering ones but it's no longer a random collection of things. My garden is still far from ideal on many levels but it is much better than it was ten years ago. You just have to keep working at it. Read a lot, especially things like garden history and about famous gardens and gardeners/designers. Visit as many gardens as you can.

In a way this is an oxymoronic question. A collector sees all of his possessions as unique which means that unity in the planting is not going to happen. Even if yours is a collection of one species it it the difference rather than the similarity that you admire. The unifying element consequently must come from elsewhere. Specimens in a museum are held together by similar framing or display case and in a garden there are a variety of ways to achieve a similar effect. My choice would be to surround the specials with ordinaries and the ordinaries could provide the unity.

The best way to start, for me, is to design the bed layout and plant the trees and shrubs that will form the back bone of the garden. If, like me, you like to collect shrubs and trees this can be even more fun. Ultimately, you will not like your garden if it is just a jumble of differnt plants with no direction for the eye to follow. Try to envision the whole landscape, and then make a plan. Once you have a direction, your plant addiction may get out of hand but you will find places for plants that you never knew you needed.
Okay, lets face, I am an enabler!

Ink summed it up for exactly what it is and what needs to be done. The only question is what this person will used to tie it together.

Look at other plantings that put a lot of variety of form, color, and texture in them that are successful. Then, ignore the plants and take a visual inventory of what else is there. Many Japanese gardens fit this description, but we tend onlt to see the plants and a few iconic elements and miss what else is there.

This question reminds me of three former clients who were addicted plant collectors. Without tearing mature gardens apart how could a 'feeling' of unity be introduced into the landscape? My solution was to install interesting, carefully designed bird houses on cedar posts strategically throughout the gardens so that a rhythm was established. These captured the eye and were an introduction to the surrounds. It is not the number of bird house intalled but the placement. At one important point in each garden I clustered three smallish bird houses together on posts of varying heights. Of course, the clients immediately planted Clematis on each post but that was okay. We collectors will seize every opportunity to add more and more to the garden.

Thanks mjsee and tanowiki. I have been thinking along this line. Yes, even a few nice rocks. I'm probably going to invest in a few nice square cut rocks - big enough that I will have to have them delivered by my local hard-scape retailer. I understand scale and will be careful. I see to many examples where the rocks are to big for the house, garden, lot.
D

Along with what others have said...

-Repeat low-growing edgers (I find that using repeating groups of an edger can unify a perennial border even if the taller plants behind them vary)

-Repeat foliage color (I find that chartruese foliage works well for this purpose, but silver foliage and purple foliage can do the same thing)

-At the beginning of a path or transition area, I often repeat anchor plants on both sides to provide a frame for what lies beyond.

Some very good points are made above. The only one I disagree with is using ground covers, because they eat other plants. But maybe a groundcover that works is out there and I just don't know about it.

As a rabid collector turned home landscaper in pursuit of sanity, I think there is a conversion that has to occur in your own mind. Ink touched on it by pointing out that all your acquisitions are unique, but what I find is you can get past this by thinking of your plants in terms of their shape/colour/size -in other words, their landscaping attributes. These are the ones you see from a distance.

For example, a hosta is a low spreading herbaceous plant or an arching one, depending on which one. A certain Chamaecyparis is a blobby gold evergreen thing. A fern is arching, a columnar yew is a vertical evergreen accent. What ANOTHER rhododendron is depends on its structure. Forget flower colour, forget bloom time. Just focus on structural attributes.

Then you take the point made by MaryMD about repetition, only you don't repeat plants, just shapes/colours. So you look around the yard from vertical accent to vertical accent, or from gold shrub to gold shrub, only you are looking at a different one every time. Similar to what Nandina suggests, only the plants do it.

This recognition is not my own, by the way, but goes back to a discussion here started by Frankie about an article in Fine Gardening about designing a long border...? Maybe that thread still exists, or maybe not, or maybe the article can be found.

The unifying effect of hardscape is also something very helpful to utilize. Just edging beds with something like a uniform brick border will begin the process of turning a collection into a landscape - partly because it will immediately make you think about the shape of the bed instead of the name of the plant. To assess the shape of the bed, you find yourself stepping back across the road (watch for cars) to assess the overall effect of the garden. That's the perspective from which you start appreciating plant shape too.

Ken Druse has written a book called The Collector's Garden. It's a long time since I looked at it so I can't summarize it, but you might enjoy it.

KarinL