I have a small garden and most of the client gardens that I work in are quite small as well. Because space is limited, we aren't able to grow every plant that catches our eye, so we have to be ultra-choosy about what we include in our gardens. So I've come up with this way of thinking about it that; for lack of a better description, I call it "the goodness ratio."
It boils down to this: the larger the plant, the more rigorous the selection process.
In our small plots we can only grow a few large shrubs and/or small trees. And what I'm looking for in these larger plants is something that will really deliver through the seasons. More than likely we're going to require that it deliver more than one of these type of attributes: spring or summer bloom, fragrance, wonderful foliage, fall color, interesting bark and/or branching structure for winter interest, and so on.
Small plants that are especially lovely and or plants that share space well might be given a bit of a reprieve, the standard relaxed somewhat. Naturalizing spring bulbs such as crocus, anemone, species tulip, and allium are a good examples of this. Or plants that peak in winter or early spring that are then a good host for a summer blooming vine.
Small trees and shrubs that earn their keep
Here is a very small, very partial list of some plants that I turn to time and time again. I encourage you to think more about the "why" they made the list so that you can then add to it, creating your own list of hard-working plants to consider using in your garden. All are recommended because they deliver through the seasons, displaying at least three of these attributes: summer bloom, attractive foliage, fall color, fabulous bark, provide a strong contribution toward structure, and they're suitably sized for city gardens.
- Stewartia psuedocamellia - Japanese Stewartia
- Stewartia monadelpha - tall Stewartia
- Lagerstroemia cultivars - crape myrtles
- Acer griseum - paperbark maple
- Acer palmatum - Japanese maples. Lots of great ones to choose from; I'm fond of Acer p. 'Sango Kaku', A. p. 'Seiryu', A. p. 'Ukigumo', A. p. 'Fireglow'
- Acer japonicum 'Acontifolium' - fern leaf full moon maple
- Viburnum plicatum tomentosum 'Maresii' - doublefile viburnum
- Hamamelis x 'Jelena' - witch hazel
- Cedrus deodara 'Silver Mist' - just one of many wonderful dwarf conifers to consider
- Choisya ternata 'Aztec Pearl' - Mexican orange, finely cut green foliage
- Choisya ternata 'Sundance' - another Mexican orange, with yellow foliage
- Ilex crenata 'Sky Pencil' - a columnar Japanese holly
- Cryptomeria japonica 'Little Diamond' - dwarf Japanese cedar
And the list could could go on and on ...but why don't you do this, check out Great Plant Picks for lots and lots of really great plants specifically recommended for their suitability to northwest gardens. But don't forget, be choosy.