A Gardening Journal

Round-leaved Vitex

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With such distinctive foliage, total tolerance of sun and salt and sand, and colorful (but tiny) flowers, round-leaved vitex seems the perfect solution to beach plantings. Depending on the mildness of the Winter, the intense (but, remember, small) blue flowers might appear in Spring, Summer, late Summer, or all year round.

 

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The shrub's striking foliage is the real performance. Pairs of silvery round leaves in orderly ranks up the low stems provide a lively texture throughout the frost-free months.

 

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Although Vitex rotundifolia is native to Asian and Australian beaches, its success at the seashore can make it a formidable competitor to native beach flora elswhere. Instead, grow this shrub in your inland garden, where its terrific visuals aren't compromised by its talents for taking over beach-front real estate.

 

 

Here's how to grow this unusual and elegant shrub responsibly as well as creatively:

Latin Name

Vitex rotundifolia

Common Name

Round-leaved vitex, beach vitex

Family

Lamiaceae, the Mint family.

What kind of plant is it?

Flowering shrub. 

Hardiness

Zones 7 - 10.

Habit

In the open, sunny, windy oceanfront habitats this shrub prefers, the growth of its wide-spreading stems is prostrate. In sheltered inland sites, growth can be more upright.  

Rate of Growth

Fast.

Size in ten years

Size is greatly affected by climate, shelter from prevailing winds, and culture (which see, below). Where prevailing wind isn't too severe, and storms are less frequent, growth can mound between one and two feet high, and extend as wide as the terrain will allow. Where prevailing wind is stiff and/or storms frequent, colonies tend to be lower, but just as widespread. In frost-free climates where prevailing wind is modest or mitigated, the outer stems of the colony still tend to grow prostrately, but the central stems grow upright, to two or three feet or more.

Height and width are reduced in climates whose Winter temperatures (or the combination of the actual temperature and the added wind chill in exposed coastal locations) are low enough to cause tip die back.

Texture

Marvelous, in that the orderly ranks of leaves maintain a certain rhythm even in colonies that are growing with maximal density. 

Grown for

its foliage: The species' name is accurate: The "folia" are rotund, indeed. They are nearly as broad as long, and with scarcely any point at the tip. The innate blue of their top surface is accentuated by a surface layer of extremely short hairs that add a silvery cast. The leaf bottoms are a bit lighter—possibly because the layer of surface hairs is denser—providing subtle "backlighting" as the foliage is ruffled in the wind. The edge of the leaves is a narrow line of pure white, adding yet another note of subtle elegance. 

its habit: Vitex rotundifolia normally grows as a low-to-prostrate groundcover, rooting frequently along its stems, and spreading widely as well as quickly. (In my sheltered inland garden, however, it is broad but upright.) Outside its native range, this prowess can enable it to be invasive. See "Downsides," "Culture," and "Where to use it" for options for growing this beautiful species responsibly as well as creatively.

its flowers: Short spikes of small (you have been warned) blue flowers are almost more enjoyable in bud—when they appear as little spikes of silvery-white BBs—than in flower.

Flowering season

In Zones 7 and 8, in Spring. In Zone 9, much of the warm months. In Zone 10, year-round flowering is possible. Flowering is delayed, sometimes substantially, when colonies are overwintered indoors. My containered shrub, overwintered dormant and leafless in the basement, flowers in September and October.

Color combinations

The silvery-blue leaves and blue flowers are most congenial with burgundy, white, silver, pink, rose, pale yellow, and, of course, other shades of blue. Strong contrasts with orange, red, and chrome yellow are possible, but are liable to look obvious or even jangling.  

Plant partners

Unless you're growing Vitex rotundifolia in a container (see "Quirks and Special Cases," below), its plant partners are determined first by their compatibility with the sunny, warm, and sandy conditions this shrub needs to survive, and only second by the aesthetics of contrasting or collaborating pairings of texture, color, scale, and habit.

Sandy soil-loving partners from warm-enough climate zones include sea grape (Coccoloba uvifera), wax myrtle (Myrica cerifera), grand crinum (Crinum asiaticum), beach grass (Ammophila breviligulata), mound lily (Yucca gloriosa), Spanish bayonette (Yucca aloifolia), flax lily (Phormium), kangaroo paws (Anigozanthos), any number of species of succulents (e.g., Euphorbia, Aloe, and Opuntia) and palms (Sago, Bismarckia, Trachycarpus, Sabal, and Cocos).

Of this enormous range, my first choices would be for those few with purple foliage: Crinum 'Queen Emma', Euphorbia cotinifolia, and Phormium 'Black Adder' or 'Merlot'.

When used, as I do, as a container plant that's sunk into a sunny and normally-draining garden bed Spring to Fall, but overwintered frost-free in Winter, there's no need to restrict plant partners to those of similar hardiness or preference for sandy soil. The only "musts" are to site the colony of beach vitex where it gets all possible sun and heat, and not to let neighboring plants, which are likely to be taller, cast shade.  Congenial partners with collaborating coloring and contrasting texture would include red shield (Hibiscus acetosella), upright plum yew (Cephalotaxus harringtonia 'Korean Gold'), and 'White Gold' and 'Ogon' spireas.   

Where to use it in your garden

Vitex rotundifolia should be planted only in inland sites where there will be no danger of its spreading by seed (which will germinate best in sandy beachfront locales) or by rooted segments that might be dispersed by wind or water.

Its best use is as a groundcover in hot and sunny locations where it can spread freely but also safely. Sites that are sloping, or are fronted by retaining walls, help provide the quick surface runoff that this species needs for maximum hardiness. Such a quick change in elevation also gives the shrub opportunity to create a flouncing cascade of stems and foliage. As long as they provide quick drainage into underlying crevices, planting pockets in south- or west-facing ledge would be ideal. Where Winters are stern enough to cause just tip die back instead of extensive kill off—the cold side of Zone 7— Vitex rotundifolia can form low, dense carpets.    

Culture

As a native of beaches throughout the Asian Pacific, it's no surprise that Vitex rotundifolia enjoys all possible sun, and is happy in heat as well as gritty, extremely well-draining, nutrient-poor soils. Approximate these conditions at inland sites by planting in sandy or gravelly soils, particularly those that include a slope to speed surface runoff. Lean soil, sharp drainage, and full sun are essential in maximizing hardiness.

How to handle it: The Basics.

Plant in Spring, ensuring enough water for establishment. Given the species' preferred native habitat—beaches that border bodies of brackish water—initial watering is probably sufficient. If used as a large-scale groundcover in ideally lean conditions in Zone 8 and above, where Winter hardiness is the norm, planting can be fairly sparse. Plants root along their prostrate stems, forming colonies larger than ten feet in diameter. Initial spacing of three to four feet should lead to coverage in two to three years.    

How to handle: Another option—or two!

Its unusual foliage combines with its prostrate and wide-spreading habit to make Vitex rotundifolia a striking oddity outside its normal haunts of seaside beaches that enjoy a mild climate. Experiment with establishing it in Zone 6 gardens—where it is unlikely to be able to spread by seed or by errant rooted sections—by siting where it receives all possible south and west sun (see "Culture," above), but also all possible shelter. Alas, sites with "all possible" sun often achieve it through lack of the surrounding buffers of shrubbery or buildings that might, otherwise, provide the year-round shelter necessary for Winter survival. In Zone 7 and colder, round-leaf vitex will be completely deciduous in Winter, as well as dormant, so the shrub could be protected by a thick covering of evergreen boughs. Your colony of Zone 6 Vitex rotundifolia could be the annual recipient of all the boughs of your year-end garlands or from your Christmas tree.

Protecting with a layer of mulch or sand would, at first, seem problematic: How would you remove it in Spring? Au contraire: a layer of sand that covers most, but not all, of the stems could be just the solution. Yes, exposed stem tips are likely to die back, but the shrub resprouts readily from old wood, and the portions of stems that you buried under the sand are likely to be viable. Topping up the layer of sand early in each Winter will bring more and more growth underground, creating a larger and larger "reservoir" of protected stems to resprout each Spring. It also ensures that the crown of the colony has a mounding slope atop it, for quick run-off of surface water.

My flat and heavy soil precludes in-ground planting—there are practical limits to how much sand could ever be added, let alone shoveled—and, because Vitex rotundifolia is normally hardy only down to Zone 7, I can't achieve the necessary drainage by planting the shrub in one of my troughs, either. Although fantastic drainage is possible with planting in a container, it is achieved at the cost of added stress on plant's roots, which will freeze and thaw much more quickly than when growing in the ground. Successful trough plantings feature horticulture that is much hardier than would be needed to survive in the ground. For marginally hardy plants, the damage of root freezes outweighs the benefit of excellent drainage.

 

Even so, I do grow my colony of round-leaf vitex in a large pot, but I bring it out to the garden only in the warmer months. Extreme drainage is only required in the Winter; when the colony is in active growth in Spring and Summer, normal soil and water are fine. Each Spring, I plant the colony in a garden bed, pot and all. By sinking the pot up to its nose, so to speak, I can draw surrounding soil up onto the colony, creating a gentle mound that sheds surface water quickly. The soil also facilitates growth of outward-bound stems and the roots they create. Between occasional rains and water absorbed from surrounding soil by these newly rooted-in stems, the shrub needs no supplemental watering. After hard frosts cause leaf drop, I dig up the containered shrub, shaking the mounded garden soil from it in the process, and stow the pot in the basement. 

Quirks and special cases

In Zone 8 and warmer, try growing Vitex rotundifolia in a large permanent container. The climate is mild enough that there won't be the fatal damage from the quick freeze/thaw cycling in a colder climate. Then, train a main stem up a permanent stake, pruning the remaining basal growth back regularly to keep the volume of overall growth within the amount that a pot of that size can sustain. Encourage the staked stem to grow to the top of the stake, and then stimulate production of side branches by pinching it. The result? A weeping standard, whose round silvery leaves and spikes of blue flowers should make it a knockout.

Downsides

Round-leaf vitex should not be planted in seashore locales outside its native range, where it can spread aggressively by seeds, by rooting along its stems, and by sections of rooted stems that break free from the mass and are dispersed by wind or water. Instead, grow Vitex rotundifolia inland, as an unusual groundcover. See "Where to use it," above.

Variants

To my knowledge, no variants have yet been identified.

Availability

Occasionally on-line and at "destination" retailers.

Propagation

By cuttings, by division of rooted stems from the mother colony, and by seed.

Native habitat

Vitex rotundifolia is native to the Pacific coasts of Asia and Australia.

 
 
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