The Best Season Ever: Upright Spurge

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Plants that self-seed into gravel are usually tough and self-reliant. Too bad that most—think of crabgrass and dandelions—are also unattractive. This unusual spurge is a welcome exception. Euphorbia stricta is very happy as a filler in front of the line of terra cotta pots along my drive. One or twice during the Summer, I weed out all the true weeds, leaving a pure stand of the spurge.  

 

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Although Euphorbia stricta is a season-long bloomer, the blooms and their bracts are green, and so don't provide a separate show from the green foliage. The bracts of many other forms of Euphorbia—such as Euphorbia millii, crown of thorns; and E. cyparissias, cypress spurge—are intensely colorful. There's also one cultivar of E. stricta to date, 'Golden Foam', and its bracts are, indeed, gold.

 

Despite its green flowers and bracts, this species is still capable of a colorful display, thanks to its stems. See how the bottom of the stem in the picture below is rosy pink? When this spurge is grown so that it reaches its more typical size—about thirty inches high and wide—the stems are this color most of their length. The show of rosy stems coursing amid all the green foliage and flowers is (if pictures are to be believed) simply stunning.

 

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Here's how to grow this unusual and self-reliant euphorbia: 

 

Latin Name

Euphorbia stricta, also known as Euphorbia serrulata

Common Name

Upright spurge; also Tintern spurge: Euphorbia stricta is widely indigenous in continental Europe and countries surrounding the Mediterranean. In the United Kingdom, it has become naturalized only near the town of Tintern.

Family

Euphorbiaceae, the Spurge family.

What kind of plant is it?

Hardy perennial that flowers and sets Winter-hardy seed its first year and, so, also succeeds as a hardy annual.

Hardiness

Reports are mixed. The species overwinters in the gravel driveway of my cold Zone 7 property, but at strikingly dwarf size. (See "Size," below.) Is the shortness related to borderline hardiness, itself, or is it due to less-than-ideal siting? (See "Culture" and "How to handle it," below.) One source confidently says that Euphorbia stricta is hardy to Zone 5, but most others describe the species as being an annual.

Habit

Young plants are erect, hence the Latin name of "stricta," which means very upright. If they survive to maturity (see "Culture" and "How to handle it," below), plants send up other stems, to form a clump. Plus, each stem sends out many side branches, which bear the flower clusters. The profuse clusters of flowers and bracts contribute far more visual bulk than the foliage. Because these clusters are only at the tips, plenty of stem lower down remains visible. 

Rate of Growth

Fast.

Size in five months

Size is dependent on climate and handling. Here at the coldest edge of Zone 7, in possibly marginal circumstances, this perennial is a six-inch curiosity. In milder climates (or in ideal conditions in any climate), Euphorbia stricta can grow into a mound thirty inches high and wide.

 

Why are the stems of my plants so short? Stems grow vegetatively before switching over to flowering when a certain proportion of day length to night length is reached as Spring progresses to Summer and the days become longer and longer. In colder climates, Spring arrives later and later, leaving less time for the vegetative growth phase. When growing from seed (either de novo or as a returning "hardy" annual), the time from germination until start of flowering would be even shorter and, so, the stem height that could be achieved would be even less. It might also be the case that my driveway isn't hospitable enough for plants themselves to overwinter, just the seeds. See "Grown for," "Culture," and both "How to handle it" boxes for how to help this species perennialize.

Texture

Delicate at any size.

Grown for

its texture: Euphorbia stricta is a prolific bloomer. The green color of the flowers and bracts differs little from that of the leaves and, so, their contribution is textural, giving the plant a fluffy and even foamy appearance similar to that of parsley.

 

its stems: My stunted specimens don't begin to tell the story. Stems, not flowers, provide this species' touch of color. They are rosy red, and are enhanced instead of obscured by the dense clusters of flowers that they support.

 

its graceful habit: When circumstances are to its liking, Euphorbia stricta forms a billowing mound that is a pleasure to view from top to bottom. My stunted specimens, hardly more than branching sprigs with terminal flower clusters, don't even hint at this potential.

 

its ease of handling: Euphorbia stricta can persist for years as a self-seeding annual. With deep enough soil and excellent Winter drainage, it also thrives as a mounding perennial. Either way, it is drought tolerant, and is ignored by browsers. This very self-reliance can enable this spurge to self-seed rampantly; see "How to handle it" for one way to control this. 

Flowering season

When stems are able to overwinter, flowering begins earlier in Spring and continues into Fall. When growing as a self-seeding annual, the start of flowering is delayed until later in Spring or into early Summer.

Color combinations

The species' overall display of light green foliage, flowers, and bracts is compatible with everything. It's the pinkish-red stems that suggest specific colors that neighboring plants might highlight: Burgundy and ebony should be the first choice, pending how pink or how red the stems appear in your garden. Then, add other hues accordingly: Either pink and rose, or orange, yellow, and red. To my eye, blue or violet would risk being too noisy, unless that plant's foliage or flowers also feature burgundy or ebony, or the rose or red that would make a strong and specific link to the euphorb's stems. Similarly, white would be irrelevant unless that plant also featured burgundy or ebony, or rose or red.    

Plant partners

Euphorbia stricta is a dramatic partner to plants that provide the necessary contrast in form, scale, and texture while also establishing a clear harmony of color. First, to form, scale, and texture: Look for plants (that also crave sun and good drainage, of course) with markedly different overall size, whose leaves are comparatively large and, preferably, of a simple shape. What about Buddleja, Cordyline, Cotinus, Gladiolus, Hesperaloe, Kniphofia, Opuntia, Verbascum, Yucca? Each of these has a form that makes explicit links either to yellow or to rose or pink, or adds burgundy or ebony. And even if color weren't a consideration, each is a terrific contrast in foliage size and shape.

Where to use it in your garden

Even as the tiny tree-like dwarf that is all this species achieves growing in loose gravel in less then ideal circumstances, Euphorbia stricta is a charming filler. When the plants are able to achieve billowing, mounding, full-size maturity, the species deserves a location at the front of a bed, so its display can be appreciated head to toe. Another option is to welcome it to stretches of gravel that permit deeper rooting and more sheltered growth, so that the same maximum size is achieved but in a more isolated—or, rather, featured—setting. See "Culture" and "How to handle it."   

Culture

Sun, heat, good drainage and, if the choice can be made, soil that has a high proportion of sand or gravel, and that is protected from becoming compacted. Such deep, loose, and lean soil provides fast drainage and also enables easy and deep root penetration, both of which enhance hardiness and, therefore, overall size.

How to handle it

As is typical for Euphorbia, E. stricta prefers not to be transplanted. Sow in situ when possible, or in deep seed plugs that you disturb minimally when transplanting to permanent locations. Germination is reported as being erratic and sometimes very slow. Mark where you sowed, and be patient. Seed can be sown in Fall or Spring.

 

As is also typical for Euphorbia, individual stems die after flowering is completed. Clip them near their base to make room for new growth. Where E. stricta is fully hardy, this might be easiest to do in the Fall, when there is no danger of disturbing emerging new growth. Where the species is more of a risk—in Zones 6 and 5, certainly—this pruning is probably best delayed until early Spring.

 

In the circumstances where E. stricta thrives, such as the mild Mediter- ranean climates where it is native, plants have the potential to self-seed prolifically. You may want to remove flowering stems in mid-Summer, before very much seed has been ripened. The very mildness of climate that permits rampant self-seeding would also permit overwintering of a second flush of growth that such clipping would probably encourage.

How to handle it: Another option—or two!

The red stems are such a good contrast to the lime-green flowers and bracts. If you're going to grow Euphorbia stricta at all, it's worth doing what you can to enable it to achieve its full dimensions and, hence, its maximal "stemminess." Assuming that the species really is hardy to Zone 5 as listed, I'm going to transplant young plants early this Spring to two of my very large and very deep troughs: One with especially gritty and free-draining soil, and the other with typical moisture-retentive potting soil.

 

When growing in a trough—essentially, a large above-ground container that will freeze and thaw regularly during a tough Winter—plants that aren't hardy enough even to survive in-ground (where their roots might freeze, slowly, just once a season) will surely perish. As a rule of thumb, for plants that you'd like to grow outdoors in troughs year-round, choose those whose hardiness is rated at least one Zone colder than would be needed for them to survive year-round when growing directly in the ground. My gardens are barely Zone 7, so plants that would survive in my troughs will probably need to be at least high Zone 5, meaning barely Zone 6. Trialing Euphorbia stricta in my troughs will, therefore, confirm whether the species is hardy to Zone 5, as that one source listed.

 

With luck, I'll have also brought along some of the species' seeds scattered nearby that are just waiting to germinate. If seeds or transplanted plants establish in one or both of the troughs, I'll be also able to determine whether good drainage per se is the key to maximizing overall size and hardiness, and whether the quicker and even larger growth that more nutrient-rich soil produces is achieved at the expense of reduced hardiness.

 

Given the satisfying top-to-bottom form of a full-sized clump, as well as the Spring-to-Fall flowering season, another option would be to grow Euphorbia stricta in a tall container that you overwinter in a cool or even unheated greenhouse. The species' love of good drainage as well as soil that doesn't stay too moist would be easily achievable—indeed, almost unavoidable—in a container that is higher than wide, and full of regular potting soil that has been cut by, say, a third with sand or perlite. Because the container would be brought into shelter before hard Winter weather, there's no danger in pruning out all of the season's currently-flowering stems in Fall. Handily, this would reduce the space the plant would need in what is, almost certainly, an area for overwintering that is already crowded.  

Quirks and special cases

The seeds of Euphorbia stricta have an elaiosome, which is an attached structure rich in lipids and proteins. Many elaiosomes attract ants, which bring them, seeds and all, into their nest to feed the elaiosomes to their larvae. The seeds themselves are then carried to the ants' waste disposal area—their compost heap, so to speak—where germination is enhanced by the rich frass of dead ant bodies and other detritus.

Downsides

Euphorbia stricta can be a rampant self-seeder. See "How to handle it," above, for how to control self-seeding.

 

As is typical for Euphorbia, stems of E. stricta exude a sticky white sap when cut or injured. The sap is toxic if ingested, and can cause a severe allergic reaction if it comes in contact with unprotected skin or, even worse, eyes. Wear gloves when handling E. stricta.  

Variants

The flowers and bracts of 'Golden Foam' are noticeably more yellow, but this cultivar does not come true from seed, so future generations will have the green flowers and bracts you see in my pictures. Given the species' ability to self-seed, growing 'Golden Foam' could be a losing battle: Unless you weeded out the volunteers relentlessly, the 'Golden Foam' plants would soon be in the midst of a swathe of the all-green species. Perhaps it's better to grow the species from the outset, celebrating its red stems and not regretting the absence of the yellow 'Golden Foam' flowers and bracts.  

Availability

On-line.

Propagation

By seed.

Native habitat

Euphorbia stricta is native to Europe and the eastern Mediterranean.

 
 
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