The picture to the left shows an evolving project in south Minneapolis we worked on two years ago. Even within this narrow space two distinct spaces are created with the wallstone wall and there is always something warm and inviting about clay pavers - here in a circular patio with soldier course. I couldn’t resist taking this picture showing the space starting to get that “lived-in” look.

What is the difference between a pergola and an arbor? If you look up the words in an on-line dictionary you will find arbor defined as something like, “A shady resting place in a garden or park, often made of rustic work or lattice work on which plants, such as climbing shrubs or vines are grown” (The Free Dictionary by Farlex). A pergola is defined as, “An arbor or passageway of columns supporting a roof of trelliswork on which climbing plants are grown.”

Landscape design writers such as Gordon Hayward and Cynthia Cash define the strict usage of the work pergola to refer to a colonnade or passageway.  About.com quotes Cynthia Cash, ”The primary difference in an ‘arbor’ and a ‘pergola’ is that an arbor is a free-standing structure (also used to support vines), whereas a pergola is a long linear structure over a garden pathway.”

Judging from images pulled up using Google, common usage of the word pergola defines it as a “substantial” columned structure which can either be over a walkway or, more commonly, over a sitting and dining space adequate for a group of people. While this could also be called an arbor, the word arbor is generally reserved for smaller structures over gateways or individual benches. Both arbors and pergolas are used as a structure to support climbing plants.

No matter how you use the words, arbors and pergolas are important elements to define, soften and divide both small and large spaces. Arbor gates create a defined transition between “outside” the garden to the intimate interior. They also frame a view into the garden at this threshold. A pergola’d sitting area, either attached to the house or freestanding, creates a defined outdoor room as well as breaking up horizontal lines of fences and garages.

One of the great things about stone is that there are such distinct regional differences. Stone one might find just laying about in a field in one region is often devalued by the local residents because they see it everywhere. In Minnesota, what we call “field stone” is a random assortment of rounded rock in all different colors and sizes. We also call it “glacial boulders”, which defines more closely the character and source of this rock.

The rounded shape and colors that range from pink and white, to blue and dark red, define its geologic past. This rock we see stacked in huge suburban retaining walls and the “river rock” we see in shopping mall shrub plantings is the result of the glaciers pulling rock from a variety of northern sources, tumbling it over thousands of years and dropping it randomly on the landscape. Its kind of like “stone washed” jeans - these rocks have a lived-in look.

While its ubiquitous nature leads to it feeling kind of common, it really is our “native rock” and can be used in ways to accentuate its nature rather than just to solve maintenance problems or cover space.

This weekend we saw the first saw fly larvae on a pine tree. Double-check your pines for this pesky pest - they are tiny worm-like larvae of the saw fly and their voracious appetites can defoliate even large trees. You can spray the tiny monsters off with a garden hose or, on larger trees, call your friendly arborist for control measures.

Shannon and I were driving to a client site yesterday via 42nd St. in south Minneapolis. WOW! The entire street is lined with crab apples - and, in this high season, is literally draped in pink and white flowers. I think our crab apples must rival the Japanese cherries in this glorious time. The flowering doesn’t last long so if you have time head down 42nd St. between Hiawatha and the river, or the east side of Lake Nokomis, or the MN Landscape Arboretum or the Japanese Garden at Normandale College.

Sometimes it takes a grove of a particular tree to express its positive characteristics. If you are driving down Colfax somewhere around the 48 hundred block you will suddenly notice a grouping of trees that give the block an ethereal feel. These are tamaracks - a tree that can easily look out of place by its lonesome, but in natural clusters takes on a totally different hue.

Many Minnesotans share a fondness for tamarack trees built up from trips to the cabin where the trees bright green early season leaves and especially the trees brilliant gold fall color make it remarkable. But few take advantage of these characteristics in their urban homes. Take a drive by the trees on Colfax and see what you’re missing.

May To-Do List

• Remove plants from their pots and untangle any roots before transplanting to your garden.
• Wait until mid-month to plant tomatoes, since frost is typically gone after May 20
• You can plant annuals after the last frost. But be sure to put them in containers or in well-drained garden soil - spaced evenly apart. Water only the soil and not the leaves. If you see any leaves with spots on them, be sure to remove them immediately.
• Postpone major pruning of trees and shrubs until next winter (unless they are broken).
• The last two weeks in May is the peak time for planting annual and tropical flowers.