Hardy Euphorbias - Part 1

Hardy Euphorbia are one of my loves in the plant world. The foliage, form and flowers are all soul satisfying. As Dan Hinkley of Heronswood Nursery said, "you can't have too many euphorbs".

Hardy Euphorbia (spurges) are part of the huge Euphorbiaceae family, consisting of more than seven thousand species in three hundred genera. Most are annual, biennial or perennial herbs; some are succulents and there are a few tropical shrubs and trees. Most of the hardy species are native to southern Europe and the Mediterranean area. Some are considered rather noxious weeds. Many of the most strange and wondrous are very cacti-like and aren't hardy in most temperate gardens.

Probably the most well-known member of this genus is Euphorbia Pulcherrima, the ubiquitous Poinsettia that makes its appearance in every grocery store around Christmas. Like the Poinsettia, most of the hardy euphorbs have flowers that are really showy bracts surrounding a specialized type of miniature inflorescence called a cyathium, consisting of a female flower surrounded by male flowers, enclosed in a cup-like structure containing nectaries. The nectar is attractive to various flies who pollinate the plants.

The fruit is a three sectioned drupe with three seeds. When the seeds are ripe, they are ejected, making gathering them a challenge. It seems that no matter how closely I watch, one day those pods are shut tight and the next they have split and the seeds are gone.

All are characterized by a milky, latex sap that can irritate the skin of the sensitive, much like poison ivy, so it's best to wear gloves when working around your plants.

I fell in love with hardy euphorbs many years ago and I wouldn't be without them in my USDA zone 7 garden. By and large, they are undemanding plants. Most of them need good drainage and some are rather marginally hardy for me, but those that I grow seem to be thriving in various degrees of shade. Most of them seed around freely, so if I do lose an adult plant in a very hard winter, there are always seedlings coming on to take its place. The evergreen species add tremendously to the winter garden with foliage ranging from silver to nearly black-purple.

Euphorbia amygdaloides var. robbiae (sometimes listed as 'Robbiae') is a perfect plant for the deep shade under shrubs and trees, although it will grow as well in sun. It spreads by underground roots, so in really ideal conditions (good soil, drainage and consistent moisture) it can be a fairly aggressive ground cover. In dry shade, however, it is quite well-behaved. The glossy leaves are evergreen for me, although they can get fairly ratty looking at the end of a really bad winter. Hardiness ratings vary with reference, but it should be hardy to at least USDA zone 6 and I've seen it rated for zone 5. The leaf rosettes remain compact, getting a bit over a foot (0.3 m) tall. In early spring, flower stems emerge from the center of each rosette, rising to eighteen or twenty-four inches (0.45 - 0.6 m), and producing pale green flowers. In my plants, the flower has almost no yellow tint, although I've seen it described as chartreuse, it really isn't. In the deep shade, it rather glows.

This same species produces another variant that is, probably, my favorite euphorb of them all. E. amygdaloides purpurea (rubra) thrives in partial to fairly deep shade. It seeds around with abandon, which delights me, since it is rather short-lived. The foliage alone is striking enough to recommend it. Smoky purple to mahogany during the growing season, it turns nearly black during the cold days of winter. The flowers are a lovely contrast. The flower and foliage colors work so well together and compliment other plants so commendably, that I've been trying to use this color combination elsewhere in the garden, using other plants whose flowers or foliage repeat the scheme.

The plants stay between a foot and eighteen inches ((0.3 - 0.45 m) tall, but the flower stems can rise over two feet (0.6 m). They seldom stay erect, however, preferring to arch out from the weight of the flowerhead.

The bright chartreuse/yellow flowers start in early April for me and last until the end of May when they fade to a more subdued chartreuse (shown in the photo above) that remains nice right through June. Like many euphorbs, the flowering stems finally turn brown and die, needing to be cut back to the ground. In this photo, you can see the purple flower stems, still contrasting nicely with the bracts and developing seed pods. I simply adore this plant and have yet to find that it does not work well with anything it cares to put itself next to. Try it with the purple leafed Heucheras for a smashing combo.

Keep an eye out for the seedlings; they all have reddish stems and two long, oval, blue-green leaves.

I've moved adult plants growing in a foot or more of rotted woodchips without their getting upset, but it's better to relocate seedlings while they are still tiny if they put themselves where you don't want them. Good, well-draining soil will produce the best plants although they will grow in pure sand and gravel. Hardiness should be about the same as robbiae.

Also with purple foliage is Euphorbia dulcis 'Chameleon'. This is a fairly new acquisition of mine. I've only had it for a couple of years; this was it's first blooming season. The foliage starts out a deep, dusky purple, without the reddish tones of E. a. purpurea. Each leaf is highlighted by a lighter stripe. I haven't noticed "marbling" in the leaves that some catalog descriptions indicate. At the bottom of this photo, just above the plant tag, you can get a glimpse of the leaves - that lighter stripe shows where they are hiding in the shadows.

It may be a normal trait and it may be the partial shade my plant lives in, but the foliage loses its deep purple tone when the plant starts blooming, however, the flower stems are nearly black - quite neat. I have seen catalog photographs depicting the flowers as a startling, bright, chartreuse-yellow or even orange. Well, the flowers on my plant were much more subdued. This photograph shows them as they are fading a bit, so they were a little brighter, but not much.

It stays fairly small, reaching about fifteen inches (38 cm) tall, with a nice rounded shape that it keeps while in flower. Flower stems extend the height somewhat. It seems to be deciduous; I thought I'd lost it last winter, although it's rated hardy to USDA zone 5, but it sprang to life this spring and grew apace. Nursery catalogs say sun, but mine is in light shade for most of the day (which may affect the foliage and flower color). I've got it in a bed with very sandy soil and good drainage.

It's too early for me to predict longevity or seeding habits (it does seem to be forming seed pods). It appears that, like most euphorbs, the bloom stalks will need to be removed as they brown off. If you like purple foliage as much as I do, give this one a try. I am thinking that it would be more effective backed by Artemisia x 'Powis Castle'than the green foliage that's behind it. Since renovating this bed is on my list, I may just give that a try.

E. characias and its subspecies, wulfenii were the species who were responsible for my euphorb lust in the first place. Many years ago, I saw a marvelous plant at Chelsea Physic Garden and found it was this species. For years after this, I searched US nursery catalogs in vain; it simply wasn't listed. Then, I saw the seeds in the RHS seed exchange list and sent for them. Luckily, two or three germinated and I managed to get one plant. A year or so later, I found it in a mailorder catalog and ordered three. Of these, at least one was wulfenii.

The evergreen foliage has a lovely blue-gray tint, especially the new growth; it becomes a bit more green as the flowering stems get older. The stems all seem to have a reddish cast that intensifies and wanes with the seasons; most noticeable on new growth. E. characias characias is the tougher of the two and has managed to survive in my garden for over ten years. I've seen hardiness ratings only to USDA zone 8, but even if the older plants get killed in a very severe winter in my cold part of zone 7, there are always seedlings hiding somewhere to replace them.

I think this was the last vestige of my E. c. wulfenii, as I did not find any identifiable ones this year. While mine always had larger heads of bloom than the species, I never have obtained the massive, solid looking flower heads that I have seen on this subspecies in the UK.

This may be due to my growing them in less than full sun and in essentially clay based soil. They are not supposed to like clay. Beth Chatto grows them in her dry garden on almost pure gravel soil amended. They definitely do not like soggy soil and those who have put themselves in damper spots simply die out during wet summers. But, in my climate, they grow quite well with only a couple of hours of sun a day.

The basic visual difference between wulfenii and the species is that the flowers are a brighter yellow and the "eyes" are not black. You can see what's been described as their "sinister" black eye in this detail of the species flower. Actually, I don't find them sinister at all; rather interesting, instead. I have noted, too, that some plants of the species have relatively long, narrow flower heads as opposed to more globular brushes.

One other thing about these plant's habits - the new foliage stands smartly at attention, but as the flower stems develop, they start to arch out and twist and curve. I have yet to be able to devise a method of keeping them bolt upright. This habit isn't ugly or anything, but it does mean that the flowers tend to prop themselves on neighbors and sprawl into more than their allotted space. Just keep this in mind when you look at your border and think one of these plants can occupy that rather small bare spot.

This is a good example of this species' promiscuousness in the garden. This plant seems to be a cross between the species and wulfenii in form, flower head size and "eye" color. The flower heads are larger than E. characias characias; the eyes are brown, not black, but also not the yellowy-green of wulfenii.

My reading on the species indicates that they cross so freely it is difficult to obtain a pure species or subspecies, so I am not even certain that I started out with pure strains in the first place. However, if you aren't absolutely picky about pure strains, all of them are lovely plants who will make an architectural statement in your garden.

Supposedly, you can propagate by seed, cuttings, root cuttings or division. I've only tried seed. I have read that if you want to divide, you need to use young plants. I can verify that the older the plant, the less success you will have digging it up to move it around, much less divide it. They develop thick tap roots which resent disturbance. I think one would need to pick a young (two year old from seed, at most) plant and then cut it back hard to force it to make new growth or die. This would be the only way to achieve a continuation of a particular named plant, but seed is much the easiest way to increase your stand.

Seed requires double cold stratification with warm periods at the start and in between. I originally started mine inside on heat and then did the refrigerator gambit; now, if I wanted to start some, I'd sow in summer and leave them outside for the winter; letting Mother Nature take care of the temperature variations. The seedlings are very similar to E. a. purpurea; reddish stems with two blue-green oval leaves on top.

A couple of cultivars are out there on the market; crosses between E. a. purpurea and E. characias. One is Euphorbia 'Jade Dragon (pictured here), the Dan Heims - Terra Nova Nurseries introduction I told you about in my article about Digging Dog Nursery. The other is E. x martini, a natural hybrid who is variable and may resemble either of its parents. The flowers really do look like a cross; color and form resembling E. a. purpurea with the dark "eye" of E. characias. Both of these are still on my wish list.

Next time, I'll tell you about some more hardy euphorbs I grow and some I don't. See ya' later!

All photos in this article except the following were taken by Marge in her garden. The following images are copyright Terra Nova Nurseries:

• Euphorbia amygdaloides var robbiae
• Euphorbia 'Jade Dragon'