For anyone like me who has a wisteria vine growing in the garden, spring is one of our favorite times of the year. Even though the beautiful flowers are somewhat short-lived, the wisteria’s elegant draping clusters of fragrant lavender or white flowers make it one of springtime’s most anticipated events. San Diego horticulturist and garden writer Pat Welch has been quoted as saying that she never plans a vacation during the spring when the wisteria vines at her Del Mar home are in bloom.
I planted lavender Chinese wisteria (Wisteria sinensis) in my garden about 19 years ago and have carefully trained and pruned it to climb up a strong wrought-iron staircase railing. The wisteria can be quite invasive and needs to be watched carefully, especially during the spring and summer, its prime growing season. You can almost watch the vines shoot out and grow right before your eyes. Without proper care and pruning, it can take over your garden. If left unattended, the vine has been known to strangle trees or even invade the interior of houses, going through boards, window frames and rain gutters.
The largest wisteria vine in the world, according to the “Guinness Book of World Records,” is more than 100 years old and weighs 250 tons. This is why it is important to remember that wisteria vines become very heavy as they grow and mature, and they must be given adequate support.
On a trip to Portofino, Italy, I was fortunate to talk to one of the gardeners at the Splendido Hotel who cared for the century-old wisteria vine that shades their celebrated terrace. Portofino’s weather is similar to La Jolla’s, but it is a little colder in the winter and early spring, so the wisteria blooms around May, which was when we visited. We sat under the ancient vine, covered in scented violet-blue blossoms, gazed out across the bay at Portofino and we knew we were experiencing something very special, something we would never forget. The Splendido’s gardener told me to aggressively prune the vine, leaving a main portion of the vine, or trunk to grow strong as its main support. This is accomplished by cutting off the top of the lead vine and letting the energy go back into forming a main trunk for the vine.
While wisteria vines can grow 40 to 50 feet, mine is only about 10 feet in length but it has a healthy, thick trunk. As the new shoots appear, I choose which ones I want to keep and prune the others away, keeping approximately 18 inches between the shoots, which become branches. The more you prune, the Splendido’s gardener told me, the more flowers you will have in the spring.
Wisterias are deciduous perennial vines that lose their leaves in the fall and early winter. When all the leaves have fallen, I do a second pruning to shape the vine. Asian wisteria prefers to grow in full sun, but can thrive in partial shade, like mine, which receives the majority of its sunlight in the afternoon. A member of the pea family (Fabaceae), as the wisteria flowers fade, velvety pods will form on the vine, under its leaves. Remember that while the wisteria may be in a family that has edible cousins, its pods as well as all portions of the plant are poisonous.
Asian wisterias are the most common type grown in the United States, with Chinese being the most recognizable. The variety was introduced from China to the U.S. in 1816. The vine fully flowers before it leafs out. As the vines of the Chinese wisteria twine out from its main vine, they do it in a counter-clockwise direction. Japanese wisteria (Wisteria floribunda), another common variety found growing in our gardens, was introduced from Japan in 1830. It has more seedpods and its vines encircle the host plant in a clockwise direction, completely opposite from the Chinese.
North America has two native wisteria vines, American wisteria (W. frutescens) and Kentucky wisteria (W. macrostachya), which are not as popular or as showy as their Asian cousins.
Tree-form wisterias are also available. The tree is actually a vine that has been trained and shaped to create a trunk, with the top portion gracefully pruned to act as a flowering crown. When I first considered purchasing a wisteria vine, I was told to purchase a potted vine that was already in bloom, so that I would be certain of its color. Purchasing a potted flowering wisteria vine will save you years of waiting, because it can take 10 to 15 years for a vine grown from seed to bloom.
Wisteria vines require moderate water and will thrive even with a considerable amount of neglect ” but do not neglect pruning! They prefer well-drained, slightly acidic soil and a light application of fertilizer ” I feed mine just once a year. A good fertilizer to use would be Growmore Organic, Flower & Bloom, or I have also used bat guano. You need a fertilizer with the phosphorus level higher then the nitrogen. Too much nitrogen will create more growth than flowers. Apply the fertilizer in the winter, a few weeks after the vine has lost all of its leaves. It is said that by over-watering and over-fertilizing, your wisteria may not bloom.
While it is getting a little late in the season right now, if you would like to enjoy two of my favorite La Jolla wisteria vines during the spring, have lunch under the wisteria-covered pergola at the Museum Café on Prospect Street and then walk next door to admire the old wisteria at the entrance of Wisteria Cottage. If you happen to be in Portofino, you will not want to miss the Splendido Hotel’s memorable wisteria vine, which I plan to revisit someday!