By Sharon Cohoon, Sunset senior garden writer

Bordering a garden with pleached trees or an aerial hedge is a centuries-old horticultural practice.  In both cases the trees are closely spaced and the effect, above the trunks, is one solid mass. 

In pleaching, side branches of adjoining trees are intertwined in one flat plane and all the rest of the branches are removed.  You get a similar effect from selecting trees with a dense habit and keeping them closely clipped to the shape of the tree; that variation is called the aerial hedge. 

Both practices create a distinctively formal look, which is probably why you don't see them much in American gardens, especially our casual Western ones.

But Irvine landscape designer Carole MacElwee used a variation of the aerial hedge in the front courtyard of Mirit and Joseph Konowiecki's garden in Long Beach. A row of Arbutus `Marina' trees were planted along the courtyard wall spaced only five feet apart.  Obviously these trees will never be able to develop full canopies, but MacElwee has no intention of letting them turn into the sheared box look of traditional aerial hedges either. 

"Gil De Santos [her Silverado-based landscape contractor] is a wonderful arborist," says MacElwee, "and he'll keep these trees pruned so they remain feathery and somewhat separate."  They'll be open enough for light to penetrate and natural looking shadows to form on the hardscape, she says.

Arbutus `Marina' is a great tree for this effect , says MacElwee.  It stays small, it has big, handsome leaves, and, of course, there's that great rich red bark.  "I love the way those trunks look when I'm inside looking out at that space," says Mirit.

Metrosideros excelsa (New Zealand Christmas tree) is another good candidate for close spacing and a similar effect, says De Santos.