The Garden Designer / Phil Wood
Sun, wind are factors when creating rooftop garden

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A: The first thing to think about is the containers. The style depends on personal taste. Do you like an eclectic look, or do you want them all to match? Containers in varying colors, styles and materials can go well together if you choose them with an artistic eye.

Lacking aesthetic confidence, consider coordinating them by selecting two or three different shapes in the same material, such as terra cotta. If you want containers to last, buy from a dealer who will guarantee that they will withstand frost.

Choose containers that are big enough to hold enough soil so they will not dry out quickly. The pots should have enough visual weight to create a presence, but keep them in scale with the size of the deck.

Most round pots for perennials and small shrubs should be at least 20 inches wide at the top and 18 inches high. Trees and large shrubs will require large containers.

If weight is an issue, choose plastic pots. Fill the containers with good-quality potting soil.

Select a variety of plants. Use conifers and broadleaf evergreens as the backbone and add annuals for flower color. Mixing contrasting leaf shapes and colors is as important in containers as it is in the garden. The following plants will thrive over time in your sunny and windy conditions.

Place taller plants first. Strawberry tree (Arbutus unedo) is a good evergreen shrub that will take exposed situations. In the ground it can reach 35 feet, although it would not grow so big in the limited root area of a pot. You may want to choose a smaller cultivar such as 'Elfin King' that will grow to 5 feet in 10 years, again under ideal conditions.

Pines also are good container subjects. Select shore pine (Pinus contorta) or bristlecone pine (Pinus aristata) for dark green foliage. Japanese white pine (Pinus parviflora) has an elegant blue-gray form. Look at Thunderhead Japanese black pine (Pinus thunbergii 'Thunderhead'), a dwarf pine. Many other dwarf conifers are good candidates for the areas where you want to keep plants low.

Deciduous trees can perform well in your situation because they will not have leaves during winter storms. Japanese maples (Acer palmatum) do well in containers. Crape myrtle (Lagerstroemia species and hybrids) would benefit from the exposure, needing warm situations to bloom well in the Northwest.

With late summer bloom, good fall color and peeling winter bark, it is an all-season plant. Crape myrtle varies in size by type from shrub to small tree. Dwarf apple trees are deciduous trees that would give you an orchard in the sky.
 
Rosemary (Rosmarinus officinalis) would provide both dark evergreen foliage and a cooking herb close at hand. The blue flowers sparkle winter through spring. 'Tuscan Blue' is an upright form, while 'Severn Sea' is a prostrate form to drape over edges of the container.

Add lavender (Lavandula species) to extend the Mediterranean theme and provide the contrast of silver foliage and summer bloom.

Tobira (Pittosporum tobira) has a shiny evergreen rounded leaf that is a great foil for other textures. It has fragrant white flowers in spring. The species may grow to 5 feet, while the cultivar 'Wheeler's Dwarf' is 2 or so feet tall.

Hydrangeas are classic container plants. Garden hydrangea (Hydrangea macrophylla) comes in a range of sizes. 'Pia' grows only 1-½ feet tall with pink flowers.

Hebe is a genus well worth exploring as a low-growing evergreen plant in containers in sun. Hebe 'Amy' is the same size with dark green leaves and lavender-blue flower spikes in August into fall.

Annuals would provide the maximum color impact in limited space over a long time. Winter pansies add cool season color. In late spring, replace them with stalwart summer bloomers such as geranium (Pelargonium) and petunia, or any of the sun-loving annuals that strike your fancy.

Perennials, herbaceous plants that come back every year, have a place in containers, too. We will discuss them another day.

Phil Wood has a degree in landscape architecture and designs and builds gardens. Call 206-464-8533 or e-mail thegardendesigner@seattletimes.com with your questions. Sorry, no personal replies.

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