Garden Notes: Looking like a cool and rainy summer

On the bright side, good weather for planting trees.

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Van Houtte spiraea —Susan Safford

Rain-heavy tall bearded irises are growing at the horizontal, not vertical. The long-range summer forecast is for wetter and cooler weather. A prediction made begs for contradiction! However, it looks as if we are going to have one of those summers. You remember, when there were three and one half beach days and the tomatoes suffered from blight? Maybe not a melon year.

 

Spiraeas

A recent conversation at the nursery concerned bridalwreath spiraea, Spiraea prunifolia. A gardener was looking for one to buy, and held a small, faded flower sprig of the plant she wanted to match. A nearby large and burgeoning shrub covered with white blossoms was gestured towards. Nope, Spiraea x vanhouttei, not bridalwreath.

So to clear up the misconception, most of the spring-blooming, white-flowered spiraea we see locally is S. x vanhouttei, Van Houtte spiraea, the most frequently planted white-flowered variety. It is commonly and mistakenly referred to as bridalwreath.

Many know true bridalwreath, S. prunifolia, as a plant of old-fashioned spring gardens at older homes. Michael Dirr, in “Manual of Woody Landscape Plants,” damns bridalwreath spirea with faint praise: “Spiraea prunifolia is an old favorite (I do not know why) growing 4 to 8 feet tall and 6 to 8 feet wide. It is an open, coarse, straggly shrub, often leggy, upright and limitedly spreading with foliage on the upper 50 percent of the plant. The foliage is shiny dark green in summer, and may turn yellow-orange to purplish bronze in fall, but is never overwhelming.” And: “I really see no use for this plant in modern gardens; it belongs to the ‘over the hill gang.’”

Oh dear — we did not know! Dr. Dirr’s informed opinion notwithstanding, many of us nevertheless hold this plant fondly in our hearts. It has clean little flower sprays of tidy, double, white buttons with a tiny green center; and the leaf is attractive. Perfect cut flowers, they are an early and welcome ingredient in spring bouquets.

The Spiraea family is comprised of (again, citing Dr. Dirr) approximately 80 species, occurring in northern temperate regions. “Spiraea, although often assessed as the stepchild of flowering shrubs, is possibly more ubiquitous in American … gardens than any shrub except the rose….”

A white flowered species, S. nipponica ’Snowmound,’ is recommended as a superior replacement for S. x vanhouttei. It forms a denser shape, with a downward-flowing, waterfall habit. As with the latter, prune after flowering.

Institutional landscapes are full of examples of the almost too numerous yellow-leaf, mounded cultivars, one of the best of which is ‘Goldmound.’ Many of the yellow-leaved varieties turn green over the course of summer as the foliage matures: To an extent the color may be maintained by frequent pruning to coax new growth.

Some of the pinkish-flowering varieties, such as ‘Anthony Waterer,’ are seen in mixed borders, like oversize perennials: dreary-looking after flowering unless tediously deadheaded.

 

Good shade

Almost every day is a good day to plant a tree, and many visit garden centers now in search of a good one to plant. Although Arbor Day (last Friday in April) has come and gone, it is chosen because the chances of success are high when a tree is planted then. This year seems likely to bring success, with the cooler than usual temperatures and higher than usual rainfall. Copious rain that started out as highly welcome has become instead almost incessant, but is lemons-to-lemonade for tree establishment.

In our temperate zone, it is the large shade trees that create the habitability of home landscapes, civic ones, and nature at large, for human inhabitants, and all the other inhabitants too. (A flowering tree or fancy red-leaved Japanese maple is eye candy, and often instills plant lust; it is usually a landscape feature, not the overall “fabric.”)

As schoolchildren learn, trees are the lungs of planet Earth, due to the carbon dioxide/oxygen exchange they create. The lungs of Earth’s inhabitants function better with plenty of oxygen and good clean air, as their evolution has instructed. Trees are also the “air conditioners” of our environments, shade trees especially.

But what is a good tree to plant? Like everyone, I have my likes and dislikes. Nonetheless, I am going to suggest some of my tree preferences. I am involved with plants and landscapes, and may have thought a little longer about trees than average nursery customers.

At the top of the list would be an oak, almost any oak that thrives in our climate. The white oak (Quercus alba) is native here; exert yourself to preserve any that occur on your property. As a genus, oaks are generally deeply rooted, so make good lawn trees, their deep-rootedness also creating insurance against heat and drought. I praise white oaks for their longevity and toughness, and the fact that they support the existence of so much of our regional biota.

The handsome zelkova (Zelkova serrata) is a good shade tree. It tolerates salt and achieves the vase shape that coexists well with structures. Zelkovas may be seen on the courthouse lawn in Edgartown.

The linden tribe and its cultivars are familiar to many. One of the best for general use is Tilia cordata. Its shade is deep, it coexists well with lawns, and it is known as pollution-tolerant.

If one can find one, the yellow buckeye (Aesculus flava) is choice, real eye candy to the tree lover, and free of the foliar blights that plague common horse chestnuts.

The tulip tree, or tulip poplar (Liriodendron tulipifera) is a large and stately tree upon maturity. I would like to see more growing on the Vineyard.

Lacebark elm (Ulmus parvifolia) is appropriate and beautiful in almost any setting.

 

Polly Hill Arboretum

Brian McGowan leads a plant propagation workshop June 17th. Space is limited; please call 508-693-9426 to register.