A Gardening Journal

The Best Season Ever: Colorado Four O'Clocks

Mirabilis multiflora flower from side Wisteria sinensis Kofuji 081215 640

 

Classic four o'clocks are so easy, stalwart, and economical—think of Mirabilis jalapa as sun-loving, heat-proof, deer-proof impatiens that you can direct-sow—that I can't resist trying more. This is Mirabilis multiflora, a species of four o'clock native from Colorado to California. Sure, the flowers are always magenta, but there's a place for that. 

 

Mirabilis multiflora flower detail from above Wisteria sinensis Kofuji 081215 640

 

Plus, the leaves are bluish, which is pretty all day long. In the pictures above, the lovely pinnate foliage is that of the dwarf 'Kofuji' wisteria; for a better view of the Mirabilis foliage, look below.

 

Mirabilis multiflora another from side 081215 640

 

Lovely and relaxed, eh? Stems of Mirabilis multiflora sprawl and, if given an elevated position, cascade. I keep my plant in a pot because, although this species is hardy to Zone 4—Quebec in eastern North America—it doesn't tolerate Winter wetness well, and thrives in much drier (if often just as cold) habitat in the Rockies and southwest deserts.

 

Mirabilis multiflora from above 081215 640

 

The purple-leaved Echeveria agaviodes 'Black Prince' has volunteered in the pot, and has persisted year by year. 

 

Mirabilis multiflora tuber detail 081215 640

 

I've since separated it from the Mirabilis. Take a look, below, at the Mirabilis in Winter: Dormant and seriously tuberous. 

 

Mirabilis multiflora tuber fingers 121315 640

 

In the cold dry climates it handles so well, tubers of Mirabilis multiflora remain almost completely underground. Since I'm keeping mine in a container that is overwintered frost-free, exposed portions of the tuber are not at risk. As is common with Mirabilis, tubers of M. multiflora can become enormous: pounds heavy and feet long. If I scrape away an inch or so of surface soil each time I repot, I would be bringing another inch of tuber up into view while also creating that additional inch of soil volume at the bottom of the pot down into which the tuber can continue to grow.

 

The endurance and drought-tolerance of this species is very much related to the tuber's ability to increase in size as well as penetrate ever deeper into the ground. Does the bottom of the tuber still experience this as "even deeper" even though (we outside observers know) that it's a bit of a trick? The tuber is growing in a pot, and some of that added deepness was created by exposing more of the top of the tuber. Is growth enhanced nonetheless because the tuber can, at least from its vantage point, grow farther downward?

 

And from the other perspective, does the performance of the plant change because more and more of the upper portion of the tuber is exposed? At some chemical and hormonal level of responsiveness to its surroundings, does the plant "know" what's going on?

 

 

Here's another and quite unrelated species—Erythrina x bidwillii—that has thrived for many years while being grown in much the same way I'm proposing for Mirabilis multiflora: Each time I've repotted it, I've exposed more of its beautifully bizarre caudex and root-mass.

 

Here's a look at one of the colorful forms of the most well-known four o'clock species, Mirabilis jalapa 'Limelight', as well as how to grow it. All forms of M. jalapa are hardy only to Zone 7—but also tolerate soil moisture levels that are typical for gardens in eastern North America. Tubers are known to survive year after year in favored spots even in New England. Even though M. multiflora is much hardier—to Zone 4—it is likely to rot when grown in the milder but much wetter-in-Winter climates typical of eastern North America.

 

Here's how to grow Mirabilis multiflora

 

 

Latin Name

Mirabilis multiflora

Common Name

Colorado four o'clocks

Family

Nyctaginaceae, the Bougainvillea family.

What kind of plant is it?

Tuberous hardy perennial.

Hardiness

Zone 4-8. Above-ground growth endures only as long as temperatures remain comfortably above freezing, but the tubers are hardy to Zone 4 provided the plant is growing in a climate that provides dry Winters.

Habit

Multistemmed and self-branching. Unlike Mirabilis jalapa, whose shrub-like plants are typically wider than tall thanks to stems that are thick enough to be self-supporting, plants of M. multiflora are sprawling and dense, with numerous slender but much-branched stems that mound up atop one another. The plants are always wider than high; they both look like and function as groundcovers. With creative siting, they could cascade voluptuously. See "Where to use it," below.

Rate of Growth

Fast.

Size in five years

When growing in-ground in a suitable climate (see "Culture," below), to eighteen inches high and four to six feet wide. In a container, size is controlled both by the container as well as the growing conditions. My plant is nearly fifteen years old, and has been dwarfed both by the small container and the comparatively dim and sodden conditions of New England, both in Summer outdoors and in the greenhouse in Winter. By comparison, the sun in this species' native Rocky Mountains and Southwest is far stronger year round, thanks to low humidity. Growth is correspondingly stronger, and the mature dimensions much larger.

Texture

In the strong sun and low moisture of its native habitat, dense enough to be effective groundcover. In the comparatively diffuse sunlight of a humid Summer in eastern North America, much looser.

Grown for

its fragrant, colorful flowers: These are narrow tubes that flare at the lip, and are similar in size and shape to flowers of impatiens. They are light magenta and, so, are brilliantly colorful; the species' glaucous foliage provides superb contrast. As is typical for Mirabilis, flowers of M. multiflora open in late afternoon and remain open until morning; on mature clumps, they open in striking numbers, hence the "multiflora" species name.

 

its strikingly long season of bloom: early April to late September. No, really.

 

its foliage: The thick, dense bluish foliage is a show in itself, which is fortunate given that the bright magenta flowers tend not to open until later in the afternoon. In climates that provide enough strong sun and heat, foliage is formed thickly enough to enable Mirabilis multiflora to function as a groundcover. 

 

its drought tolerance: Thanks to a woody taproot that, in time, becomes enormous as well as deep, plants of Mirabilis multiflora growing directly in the garden need no supplemental irrigation even in the dry-to-desert climates where the species is native. Plants grown in containers are likely to need occasional watering.

 

its poisonous nature, top to bottom—seeds, too—which makes it unpalatable to browsers. In my experience, the foliage stays pristine the entire season.

 

its appeal to pollen- and nectar-foraging wildlife, such as nocturnal moths and bees that are active at dawn and dusk. As is typical for blooms that are narrow and trumpet-shaped, flowers of Mirabilis mutlflora are also visited by hummingbirds. And in a first for the hundreds of plants profiled to date in "Geek," the flowers are notable for attracting quail.

Flowering season

In its native range, Mirabilis multiflora can flower from mid-April through September, which is possibly the longest flowering season of any hardy plant native to North America.

Color combinations

Its magenta flowers and bluish foliage make Mirabilis multiflora a natural for any context that is celebrating pink, white, blue, and burgundy. Those very colors also rule out deeper shades of yellow, plus all shades of orange and red.

 

See "Plant partners" for ideas.

Plant partners

When growing in a container, Mirabilis multiflora is best as a soloist: It needs repotting every year or so, is dormant in the Winter (and, so, can be stored out of the sun), and needs infrequent watering. Plus, its sprawling stems could smother plants that aren't sufficiently tall and vertical.

 

When growing in the garden, those same sprawling, branching, spreading stems are as important a consideration as the strong color of the flowers. Adjacent plants that are also mounding, or whose stems are horizontal enough, are likely to provide perch for stems of Mirabilis multiflora, which, remember, could grow two or three feet in all directions. And, because this xeric perennial grows in the same climates and terrain of many a spiny succulent, even upright succulent stems could become frothed with Mirabilis stems that can thread their way through spines or thorns that are long enough.

 

Instead, think of partners whose lower two or three feet are spare, smooth, and vertical—and whose preferred yearly pattern of water use is similar. Most forms of Yucca or Agave will be inappropriate unless and until they form a trunk and, so, don't bear foliage until a couple of feet above the ground. Otherwise, their stiff, motionless, and more-or-less horizontal lower leaves would be at risk of being overrun by adventurous Mirabilis multiflora stems. Medium and shorter grasses are at risk, too. Taller grasses with upright foliage would be terrific. Choose among forms of Andropogon, Calamagrostis, Panicum, and Schizachyrium; even better, these forms' plumes tend toward shades of burgundy and soft pink that will harmonize well with the magenta flowers and bluish foliage of Mirabilis.

 

Larger forms of Phormium could be exciting, too, especially those with dark leaves; this combination will work only at the very warmest—Zone 8—limits of the range of Mirabilis. Even so, you'd need to remove the flower spikes of the Phormium, because the blooms are red. If you also keep a containered Phormium, though, the pairing is easy, because they rarely flower.

 

Also in Zone 8, you could underplant Parkinsonia trees with Mirabilis: The trees cast only light shade, and are native to the warmer portions of this perennial's Arizona range. Because it's hardy to Zone 7, Caesalpinia gilliesii is another possibility. Its flowers' petals are pale yellow, which, while it doesn't closely ally with blue and magenta, doesn't clash either. Do its extraordinarily long raspberry-colored pistils go with magenta, or would they read as cherry-red instead? I grow both of these species in containers that are summered in the garden. I'll place them side by side in 2016, and report back.

Where to use it in your garden

Mirabilis multiflora is a tough, critter-proof, and easy groundcover in its native southwest United States. The sprawling stems of colonies growing in-ground can become four to six feet wide each season, making this species a good choice for large-scale coverage. The bluish foliage, showy flowers, and unusually long season of bloom also suggest use as a specimen, particularly if stems can cascade down steep slopes or from atop retaining walls. 

 

In coloring, sprawling habit, hardiness, origin, and length of flowering, Callirhoe involucrata can be used similarly. In my experience, it is more tolerant of the Winter wetness typical of of gardens east of the Mississippi. I'll never forget the site of a south-facing streetside retaining wall across the entire width of a modest (and only modestly gardened) property in Connecticut, with Callirhoe overflowing side-to-side so happily that it had rooted into the narrow sidewalk-free strip at the base and threatened to flow right out into the street. I'll profile this species soon, plus its pure-white cousin, C. alcaeoides 'Logan Calhoun'.

 

Where Winter conditions are likely to be too wet for Mirabilis multiflora to succeed in the ground, plants can thrive for years in containers.

 

Given its sprawling, groundcovering prowess, it is unwise to associate Mirabilis multiflora closely with anything other than plants that are tall enough to be unaffected by its outward-bound tide of dense growth. In its native range, where it tolerates some shade, these taller partners could be sited on any side of a Mirabilis clump; indeed, the clumps can be planted as a groundcover beneath or at least in front of these taller plants. In climates with less intense sun, though, it is probably wisest to site these taller partners only to the east or north of the Mirabilis clumps, so that the perennial receives the maximum amount of south and west sun. See "Plant partners," above.

Culture

Summer heat and sun. Light shade is tolerated and even welcomed where the plant is native, possibly because humidity is typically low there and, therefore, the effective sunlight is more intense.

 

When growing in a climate that provides dry Winters, almost any soil is enjoyed, from sandy and loose to compacted and heavy. Where Winters bring more moisture, soils and siting need to provide better drainage. I haven't experimented with multiple plants of Mirabilis multilflora to see, if provided extremely sandy soil and sited so it receives impeccable drainage, whether the species can be grown outdoors without protection from Winter wet here in New England. Given that it is hardy to Zone 4 when it does enjoy sufficient dryness in Winter, survival in New England should be possible in those special conditions. Mirabilis multiflora would be an excellent trial for gardens in coastal areas where the ground is predominantly sand, such as Cape Cod. My sole potted specimen overwinters dormant, dry, and happy in the greenhouse. See both "How to handle it" boxes for more thinking.

How to handle it

Mirabilis multiflora sets little fertile seed even when growing in its native habitat, where pollinators will be those with which it can collaborate most naturally. So it is usually purchased as young plants. 

 

Install these directly in the garden in Spring, ensuring water for establishment. Plants aren't likely to need more than the initial watering and perhaps one or two as follow up in a couple of weeks to be set for life. Supplemental irrigation is unnecessary.  

 

When growing in a container, choose one that is deep rather than wide: Mirabilis multiflora is tap-rooted. Do any potting or transplanting in early Spring when new growth is just emerging. Because the species hails from xeric habitats, provide water as you would for a classic desert succulent: Let the soil become dry and the pot become appreciably lighter before the next watering. Although this species will grow in just about anything in its native habitat, err on the side of greater drainage for the potting medium for growing Mirabilis multiflora in a container. Perhaps cut garden soil by half with compost, and then by half again with sand; then add some handsful of pea gravel. 

 

Reduce water as growth slows in shorter Fall days; let stems die naturally before clipping them off. Withhold water late Fall to late Winter or early Spring (or until you see new stems emerging). The containered dormant plant can be stored out of direct light, too, which frees up that bit of always-scarce room in a windowsill or on the greenhouse bench. 

 

As is usual with plants from xeric habitats, try not to encourage the start of new growth by watering. Instead, bring the container into warmth and all possible sun in late Winter, and then be alert to the emergence of new stems. Only then provide a light watering.  

 

Water only as needed to foster new growth until you can place the container outdoors in full sun. Especially when growing Mirabilis multiflora outside its native range, with Summers that could be wetter and cloudier, choose sunny spots in the garden that are heat sinks. Can the container sit on paving and with a masonry wall to its north or east?

How to handle it: Another option—or two!

Mirabilis multiflora forms a woody tuber and, in general, the larger it grows, the greater bulk of stems and flowers it can support.  If you're growing this species in a container, encourage increase in the tuber's size by choosing a container that is deep not broad. Before new growth is evident in late Winter or Spring, gently knock the soil mass out of the pot to check how much of its volume is being filled by the tuber. Consider repotting when you see signs of the bulges and side-arms of the tuber at the sides of the soil mass, not just the bottom. Even so, don't repot over-generously, lest there be too much "unused" soil around the repotted tuber that first Winter, which could retain a possibly rot-inducing amount of moisture.

 

Even so, after years of gradually larger containers, someday there might be limits to the size of pots you have room for or can handle easily. To increase the apparent volume of soil for the deeper portions of the tuber, try dislodging the top inch or so of soil from around the upper portion of the tuber each time you repot. You'll be raising the top portion of the tuber farther and farther up out of the soil so that the lower portion can experience an extra inch or so of depth. Plus, the exposed tuber has a gnarly appeal all its own when the plant is leafless and stemless all Winter long.  

 

When Mirabilis multiflora is growing in-ground, the upper surfaces of its tubers do not emerge from the soil appreciably. This is fortunate if you have a mass planting: For Fall clean-up, sever all the dead stems quickly by using your lawn mower. 

Quirks and special cases

The seeds are as poisonous as the foliage and flowers. Use caution when planting Mirabilis where small children and pets are present. 

 

When growing directly in the ground, M. multiflora develops a taproot that is enormous and deep. Its bulk and depth are two reasons this species is so drought-tolerant; that same bulk and depth make established plants difficult or even impossible to transplant.

Downsides

None apart from the possibility that animals or children will ingest the seeds or leaves.   

Variants

I'm not aware of forms of Mirabilis multiflora other than the straight species. Oh, for even one—and, preferably, with white flowers.

 

In contrast, there are innumerable forms of the most well-known species of the genus, Mirabilis jalapa. The flowers of 'Alba' are pure white; those of 'Lemon Swirl' are sectioned radially—like pieces of pie, in other words—in white and pale yellow. Flowers in the 'Marbles Mix' are a jumble of anything from white to pink to yellow to apricot, which is wonderful if jumbling is your goal, or you want to save the tubers of specific plants to site them more distinctly next season. Flowers of 'Marrakesh' are, by comparison, a more restrained profusion of stippled and striped multi-colors of "just" yellow, orange, and pink. Flowers of 'Limelight' are magenta, and the foliage is acid yellow.

 

Flowers of 'Salmon Sunset' are more restrained still, at least in terms of normal Mirabilis palettes: Pale orange petals change mid-field to a star-shaped zone of pink but then, at the central eye, change again, to a Kool-aid shade of orange-rose. Despite the name, 'Red Glow' is deep cherry rose, with a pink star around the eye like 'Salmon Sunset'; it could be the same as the more accurately named 'California Wild Magenta'. Many years ago but never since, Plant Delights Nursery listed 'Baywatch', a yellow-flowered form that they described as growing to six feet tall. Ah, to have had the foresight to have bought it. 

 

There are countless naturally-occurring variants of Mirabilis jalapa—often among flowers of the same plant—with flowers that are striped or dotted in a, shall we say, care-free range of colors. These are perfect for situations where novelty and exuberance trump all, as well as for growing trial plantings so you can select plants whose tubers you want to harvest, to carry over those individual inspirations from year to year. In this sense, Mirabilis is just like x Pardancanda norrisii, whose flowers are as variable in both color and pattern. A generous grouping of either plant in mixed colors is likely to contain one or two that are your new favorites, which you'll want to separate out and propagate into large, pure patches.

 

Despite the wide range of colors—white, pink, rose, yellow orange—that Mirabilis flowers bandy about with such freedom, the available hues are all "candy" shades: bright and sugary. To my knowledge, there are no cultivars with flowers in darker and, in all senses, deeper colors, such as burgundy or chocolate. There are also no blues or indigos, either. 

 

Several other Mirabilis species are worth seeking out. Plants of M. longiflora bear strikingly long and narrow white trumpets, with a tiny raspberry eye.  

 

The flowers of M. coccinea live up to their name. "Coccinea" means scarlet, and this species' flowers certainly are; to my knowledge, their color is unique in the genus. Alas, the plant is a desert native, like M. multiflora, and is unlikely to thrive outside that habitat unless you can proxy the necessary conditions—strong sun, well-draining soil that is allowed to become very dry between waterings—in a container that you overwinter safe from any Winter wetness your climate normally provides.

 

Mirabilis nyctaginea is likely to be happy in midwest and eastern American gardens: This species is native to central Illinois. True to its Mirabilis worldview, its flowers are magenta; plants are reported as growing four feet tall. 

Availability

Online and, likely, at retail nurseries where the species is native.

Propagation

Young plants are far more available than seeds, which are not readily produced even when plants are growing in their native range and, hence, would be pollinated by their preferred forms of birds, butterflies, moths, bees, and hummingbirds. Although seeds of M. jalapa can be direct-sown to sprout quickly, seeds of M. multiflora need to be scarified or stratified for successful germination. Plants can also be propagated by soft cuttings as well as tuber divisions.

Native habitat

Mirabilis multiflora is native from Colorado south to Texas and northern Mexico and west to California. 

 
 
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