by Leslie Cox; Monday; August 7, 2017

Euphorbia griffithii 'Fireglow'One is hard pressed to find another genus to rival Euphorbia. Containing over 2,000 species, it is one of the largest of the plant genera. It is also one of the most varied.

Ranging from annuals to perennials, from small rock garden groundcovers to towering trees over 70 feet (21.3 m) tall, from desert-dwelling to aquatic, from prickly succulents to species with cordate-, lanceolate-, or linear-shaped leaves, this genus has it all.

Respectable low-growing mounds look lovely at the front of the border; prostrate mat-forming varieties drape wonderfully down a barren concrete wall or across a rockery. Stately columnar forms provide vivid focal points in perennial borders while beautiful cultivars of Euphorbia pulcherrima, or poinsettia, grace festive tables at Christmas. Some species are evergreen or semi-evergreen, others disappear for the winter to brightly reappear in spring.

Unfortunately, with the good comes the bad. All euphorbia species are toxic in varying degrees. They contain a milky sap that can be irritating to the skin and, if in contact with the eyes, can cause temporary blindness. It is advisable to wear gloves and protective eyewear when handling any of the euphorbias.

Euphorbia 'Blackbird'With such a diverse group of plant species, there is sure to be at least one for any soil type and hardiness zone. Be forewarned that some species are extremely invasive if given the right conditions.

One excellent example is Euphorbia ‘Fernwool’. Hardy to Zone 4 with a preference for well-drained soil and tolerant of drought conditions, this vigorous euphorbia can be a real menace if turned loose in the garden as one friend has discovered to her horror.

Originally planted in deep shade under their deck, ‘Fernwool’ has expanded its territory under the steps and is making advances across gravel paths and into another pristine area of the garden. Who of us has not experienced such invasive behaviour in other plant species?

Euphorbia polychromaFraught with these dangers, euphorbias are all that more desirable for some daring gardeners. Thankfully, there are endearing species even amongst thugs. One recommended favourite is Euphorbia polychroma (syn. E. epithymoides). While the flowers are quite insignificant as with most of the euphorbia species, its yellow bracts are truly illuminating in the spring. Pruning just the flowering stems right back when they are spent has kept this plant in a respectable 18×24 inch (46×60 cm) bushy mound. Hardy to Zone 4, this cushion spurge is reasonably drought-tolerant in well-draining soil. Ours is in full sun all day but partial shade is okay.

Euphorbia amygdaloides 'Purpurea'Euphorbia amygdaloides ‘Purpurea’ is also planted here and there in our garden. Growing roughly 24-30 inches (61-76 cm) tall, depending on soil conditions, and 12 inches (30.5 cm) wide, its slender purplish-red leaves provide a great backdrop for a number of other plant species. First year plants have green leaves that darken to purple in fall and remain purple throughout. This wood spurge is a polite self-seeder and easily controlled by deadheading spent flowers. Hardy to Zone 6, it does well in sun or partial shade.

Euphorbia characias subsp. wulfeniiAn all-time favourite is Euphorbia characias subsp. wulfenii. Linear blue-green leaves greatly enhance large dome-like flowers that appear in its second year. Held aloft on 4 foot (1.2 m) tall sturdy stems, the yellow-green bracts catch your attention even in the middle of a busy border. Allow this one about 3 feet (0.9 m) to spread out and give it protection from wind. Hardy only to Zone 7, it is the most finicky euphorbia in our garden. We lost the initial wulfenii to the prevailing southeast winds in its second winter. I did manage to collect seeds from it that fateful year and had already started new seedlings early the following spring. Originally thinking the problem may have been drainage related, we amended the area with sand. Fully grown now, this new wulfenii is faring somewhat better although it is not fully protected from the wind. Our best-looking wulfenii is one planted right under the eave of the house out of the wind and where it does not get a lot of water.

Euphorbia griffithii 'Fireglow'For the brave gardeners among us, there is Euphorbia griffithii ‘Fireglow’. It is absolutely gorgeous in the garden, but do not plant it and forget about it. Spreading rhizomes will carry this species through the border although not nearly as aggressively as ‘Fernwool’. Whatever its faults, this cultivar makes keeping an eye on it worthwhile. Bright red stems show off slender dark green leaves with pale red midribs in spring  before orange-red flowers with small yellow centers or cyathia, appear in summer to really set the bed on fire. Its autumn colour is not bad either. Looking as if its yellow leaves have been lightly air-brushed with blood, it is still a knockout as the garden begins to fade. Hardy to Zone 4 with some claiming Zone 3, it does not mind heavy clay soils, full sun, and infrequent water.

Euphorbia griffithii 'Fireglow'

Euphorbia myrsinitesWhen it comes to the dwarf versions of this species, they do not get much cuter than Euphorbia myrsinites or donkey-tail spurge. Its nickname is descriptive of the trailing stems with numerous small, pointed, blue-green leaves spiraling up their length. Reaching only about 6 inches (15 cm) tall, it happily gambols a foot (30.5 cm) or so along the top of a stone wall. Yellow-green flowers brighten its branch tips in spring. This one is hardy to Zone 5 and prefers well-drained soil. Keep an eye on its progress and deadhead spent flowers. This species has made it onto a few of the noxious weed lists in the American Midwest.

Euphorbia amygdaloides 'Purpurea'With talk of toxicity and invasiveness, many gardeners may well shy away from the variety this genus has to offer. If properly researched and handled with care there is no reason to ignore the possibilities certain species can add to the landscape design. Even ‘Fernwool’. Confined to a pot, it lends its delicate feathery foliage to a lovely grouping under our grape arbour where we like to enjoy a quiet afternoon cup of tea.