Plant Taxonomy of Purple Wood Spurge:
Estimates of purple wood spurge's average height at maturity vary wildly, but my plants stand about 12 inches tall after 7 years. The stems are ringed by leaves, the beauty of which is the main reason gardeners might wish to grow this perennial. Its foliage is dark enough for us to be able to classify Euphorbia amygdaloides 'Purpurea' as one of the so-called black plants. Plants typically bloom in early May in my zone 5 garden.
But when I say "bloom," understand that what makes the inflorescence noteworthy is not the actual flowers (which are yellow but insignificant) but the accompanying chartreuse bracts. Clusters of these appear atop the plant's red stems, which afford quite a foil.
Unlike many plants, the new foliage in spring is lighter (red to burgundy) than what follows (it is also lighter than any old leaves that may remain). The coloration after the initial leafing out becomes a deep purple-green.
As I said, stems start out red, although they lose this coloration in summer. Likewise, the leaves become progressively more green as summer advances. By August the leaves will be totally green, albeit a green that is dark relative to the coloration on most green plants.
The foliage becomes a very dark purple-green again in the fall.
By November, in some years, I detect an interesting pinkish-red on the bottom leaves, while the rest of the leaves assume a purple color. If December is cold, the stems of my wood spurge will start to droop over, and the deterioration will eventually spread to the leaves.
But during a relatively warm zone-5 winter, some of foliage of Euphorbia amygdaloides 'Purpurea' will remain healthy and assume a black-purple color that is quite alluring. I imagine that people who garden in warmer areas can count on this feature annually.
Planting Zones for Wood Spurge:
Sun and Soil Requirements:
Grow this dark-leaved perennial in well-drained soil of average fertility, and grow it in full sun to partial shade. If you're able to provide it with full sun, leaf color may be superior. Note that I grow mine in an area of my yard that receives more shade than is ideal, so my report (above) on color changes may not exactly parallel that of other growers.
Uses in Landscaping:
Caveat or Added Benefit?
Euphorbia amygdaloides 'Purpurea' is a poisonous plant. Once you are aware that these plants are related to Christmas poinsettias (Euphorbia is a huge genus), their toxicity should come as no surprise. Many people have an allergic reaction to poinsettias. Both wood spurge and poinsettia exude a milky, white sap when damaged.
The latex in purple wood spurge can irritate the eyes and skin upon contact. It is also poisonous to eat. Parents of small children should think twice about growing this perennial if the children will be spending any time in the yard without vigilant supervision.
The flip side of purple wood spurge's toxicity is that it is a deer-resistant perennial; the deer know better than to eat a poisonous plant. Rabbits and various other pests reputedly won't eat it, either.
Purple wood spurge is not especially amenable to pruning, nor do I feel the need to prune mine very often (since it's not a large plant). You can prune it, but don't expect re-growth to occur quickly. Furthermore, the plant blooms on the previous year's growth, so if you do decide to prune (and if you value the flowers), wait till after the blooming period to do so. Under some conditions, the plant may get leggy enough at some point that you will wish to prune it to restore compactness (although I haven't had this problem, myself).
Cleanup is a separate issue from pruning. I do cut off the flower stalks in June after they dry out and become less attractive. Also, in spring I remove damaged portions of stems that have succumbed to the winter cold.
Euphorbia amygdaloides 'Purpurea' readily self-sows -- a little too readily for some gardeners' tastes. Unless you want it to spread, you'll find that you have to pull new seedlings continually. Thus I would not include this plant in my landscape if my main goal were low-maintenance landscaping.
Divide in early spring if overcrowding occurs.
As indicated above, the value in growing this plant lies in its dark leaves. Moreover, it's interesting to watch the color evolve as the seasons change. Since the foliage will retain some color during the wintertime, wood spurge could be considered a "winter interest" specimen in areas that don't receive much snowfall (in areas with heavy snows, the plants will be buried and therefore out of sight, which strips them of any visual interest that they would otherwise have).
More on Wood Spurge and Related Plants:
The common name for Euphorbia amygdaloides 'Purpurea' is variously given as "purple wood spurge" or "purple-leaved wood spurge." The word "spurge" is related to "purge" and refers to the plant's medicinal usage, traditionally, as a laxative (or "purgative").
Don't confuse this plant with Pachysandra terminalis, which sometimes bears the common name, "Japanese spurge"; they are not related.
But Euphorbia amygdaloides 'Purpurea' is, in fact, related to a number of plants that you may know (even if not by name, necessarily). For example, spotted spurge (Euphorbia supina) is a small, mat-forming, ground-hugging weed that I frequently encounter at the edges of lawns, roads and paths. Cypress spurge (Euphorbia cyparissias) is a taller weed with which I am also very familiar here in New England. Leafy spurge (Euphorbia esula) is considered one of the worst invasive plants in the U.S.
In addition to wood spurge, other types of spurge used in landscaping include:
- Leatherleaf spurge (Euphorbia amygdaloides var. robbiae)
- Cushion spurge (Euphorbia polychroma)
- Mole plant (Euphorbia lathyris)