Wind break on a roof deck: Evergreen will foil the elements

Q. My husband and I recently purchased a home with a lovely roof deck. The view is spectacular, and we hope to use the space for entertaining all year long.

The problem is wind. Fairly strong gusts regularly buffet the deck.

I'm thinking that some sort of windbreak plantings in large containers might be the solution.

Since the wind seems to come mainly from the south and southwest, we could concentrate the planter boxes along one wall and corner, creating both an effective and aesthetically pleasing solution.

But, what do we plant? It would have to be hardy enough to withstand the elements on a Seattle roof year round. Also, would you recommend a particular type of planter box over others?

A. Your question reminds me of the rows of Lombardy poplars that I see planted as windbreaks on farms in Eastern Washington. Those trees would not survive in a rooftop planter, but I think we can find some that will.

Start by looking for plants that are large enough to work as a wind screen right away. Look first to evergreen plants, whether conifers or broadleaf evergreens. Their leaves would stand up to the wind better than deciduous ones, and they would provide year-round shelter.

I think the best conifers would be pines. Shore pine (Pinus contorta) will do well in a container and will provide a dense screen of evergreen branches. Other pines to look at are bristlecone pine (Pinus aristata) and lace-bark pine (Pinus bungeana).

A good broadleaf evergreen is strawberry tree (Arbutus unedo). It is a handsome shrub or small tree with glossy dark green leaves and small greenish-ivory urn-shaped flowers in October. Strawberry trees would take light pruning to keep them dense.

Another plant to consider is Southern magnolia (Magnolia grandiflora). Grown as a multi-trunk specimen, it can make a good screen. Mexican orange (Choisya ternata) is also an attractive broadleaf evergreen with fragrant white flowers. It may not be available in a size taller than a few feet; you would have to be patient for this one to grow.

Other broadleaf evergreens to look at are bay laurel (Laurus nobilis) and Pacific wax myrtle (Myrica californica).

Ceramic containers are hard to beat for deck planters. They are attractive and, if you choose high-quality pots, they will never need replacing. If weight is an issue on your deck, you might also look at pots of lightweight plastic or fiberglass.

Wood planters can be custom built to fit into your space. Since wood is subject to rot, lining them with galvanized sheet metal would prolong their life. I have also used asphalt emulsion, a water-based roofing coating, to paint the inside of boxes.

Consider constructing a physical barrier as a backup to the plants. Glass panels placed into a railing would cut the wind and still allow the view. A trellis, an open framework of wood, could slow the wind while still letting in light. The trellis would be a great place to grow climbing plants. Wisteria does well in a pot and is happy in the sun.

To keep large plants from tipping over in the wind, tie them to a trellis or railing. When tying them, use stretchable ties such as rubber or elastic cord. I learned this the hard way, when I tied evergreen magnolias to an iron fence with rope. In a strong wind, the trees snapped at the point where they were tied because there was no give.

Once you have established your screen, you can grow more delicate plants in the shelter it creates.

The possibilities are endless. Most nurseries have examples of great plant combinations for containers. For a finishing touch, Japanese maples will do well in containers if you are looking for a deciduous tree large enough to cast some shade.

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.