The poinsettia plant is associated with Christmas in many parts of the world, as is the decorated fir tree. Here in Hawaii, we can grow this member of the Euphorbia genus and her cousin snow-on-the-mountain, in our gardens year-round. The two planted together create a striking display during the holiday season. This time of year is a good time to consider planting this holiday duo for a lovely show starting in early December next year.
The close family ties between snow-on-the-mountain (Euphorbia marginata) and poinsettia (Euphorbia pulcherrima) mean that they booth bloom at the same time of the year. Bud formation is triggered by cooler weather and longer nights. Both need twelve to fifteen hours of darkness for at least fourteen days to bloom. In Hawaii, we usually get those longer, cooler nights, starting in mid-November.
Several other Euphorbia also bloom at this time and have white flowers. Pono-puno (Euphorbia leucocephala) is also considered a good accompaniment to poinsettia with its contrasting brilliant white flowers.
The Euphorbia genus has nearly 2,000 members making it the second largest angiosperm genus. Most Euphorbia are tropical or subtropical plants that share a similar flower structure and have a milky sap that can be irritating or poisonous. Snow-on-the-mountain and poinsettia share many of these characteristics.
The white snowball appearance of the marginata makes it an ideal companion to the red poinsettia as well as some of the other pulcherrima cultivars including the pink and variegated ones. The deep color of the poinsettia blossoms is a delightful contrast to the mostly white snow-on-the-mountain.
Marginata is an attractive shrub you might also consider growing alone as a specimen plant or in a group as a hedge. It can grow to over five feet tall in either case. In our tropical climate it is easy to grow outdoors.
Like others in the genus, snow-on-the-mountain has a “flower” that is technically a cyathium. This name is applied to the specialized “flowers” that form the inflorescence of plants in the Euphorbiaceae.
The tiny true flower is surrounded by bracts that dominate and actually serve as colorful petals that attract pollinators to the plant. Snow-on-the-mountain’s tiny flower is light green, nearly white, and surrounded by leaves with bright white margins. Though the true flower is quite small, the overall effect is a mass of white blossoms. This is what creates the remarkable appearance of this shrub.
Native to the western U.S., snow-on-the-mountain can thrive in a range of tropical or sub-tropical climates. In temperate climates the plant remains quite small. It may bloom in summer and must be replanted annually in these locations. Here, however, it can grow taller and thrive outside year-round.
Though sometimes considered a small shrub, snow-on-the-mountain can grow to nearly six feet in favorable conditions. It does will in full sun, planted in soil that drains well. It usually does well at upper elevations, though it can also grow well at lower, drier and hotter elevations in partial shade.
Many Euphorbiaceae. including marginata, qualify as xeriscape plants. They can usually tolerate long dry periods, once established. Though drought tolerant, they are not wind or salt tolerant. Avoid planting them too close to the ocean or in high wind areas.
The characteristic white sap of many of the members of this genus is toxic in marginata to both humans and livestock. The positive result of the presence of toxic sap is that the plant is relatively pest free. Caution is advised, however, when trimming or pruning branches. Wear gloves and protective clothing to prevent skin irritation. Dispose of the cuttings carefully and avoid ingesting the sap as it can cause severe symptoms.
Snow-on-the mountain is easy to maintain. It needs little water and only occasional light fertilizing. Her pest problems are minimal. Once the plant is mature, light pruning in spring and again in late summer can be done to encourage flowering.
Like the poinsettia, snow-on-the-mountain has a relatively short winter blooming season. If you bought a poinsettia this holiday season, you can definitely plant it in your garden as part of your 2023 holiday display.
Wait until the poinsettia begins to fade and starts to drop its leaves. By early spring, you can prune it back to a few of the main stems. By August, it should have new leaves and stems. Prune again, less severely, and it will put out new branches to support the winter flowers.
Snow-on-the mountain’s reddish stems and round form make it an attractive asset to the garden all year long. The lower leaves are usually about two inches long and green. The upper leaves can be entirely white, have white margins or white variegation. The overall effect is a white snow ball when in full bloom.
Following snow-on-the mountain’s winter flowering, a hairy, three-lobed fruit will form. The fruit contains many tiny gray seeds that can be used to propagate new plants. Allow the fruit to dry on the plant and save the seeds inside to sow either in pots or out in the garden. The young plants grow slowly but, if they germinate by early spring, they may produce flowers in the first winter.
Getting one in the ground soon, along with a poinsettia, will almost guarantee a holiday show in 2023. Right now, when snow-on-the-mountain is still in bloom, it is popular in the nursery trade. Most nurseries either have plants or can order them for you now.
Consider planting this pair now in preparation for a lovely show next December.
Diana Duff is a plant adviser, educator and consultant living part time in Kailua-Kona