When a Crown of Thorns Refuses to Branch

Standard

Photo: Rachel Bernier

Question: I bought this plant about 2 years ago (it was much smaller then!), but it just keeps growing upward. How do I get it to branch out instead of producing a single central trunk?

Rachel Bernier

Answer: Your plant is a crown of thorns (Euphorbia milii), also called Christ thorn. There are many cultivars with flowers in all kinds of colors and also varieties that branch a lot while others, like yours, rarely seem to branch at all. In my experience, thin-stemmed, small-leafed varieties tend to branch more readily than large-leaved, thick-stemmed varieties like yours.

To force your plant to produce branches, cut off the top. That eliminates “apical dominance” (when the main central stem is dominant over side stems) and forces the redistribution of growth hormones that will hopefully stimulate a few dormant buds further down on the stem to start to grow.

You can simply “pinch” your plant (using pruning shears: this plant is too thorny to pinch with only your thumb and forefinger!), that is, simply prune off the growing point, or you could cut the plant back severely, to maybe 4 inches (10 cm) from its base. That will force your crown of thorns to produce at least one branch and probably several.

Wear gloves when pruning a crown of thorns: not only is the plant very spiny, but its sap irritates the skin and is even poisonous if swallowed. And after pruning, spray the wound with cold water to cause its white sap to coagulate and stop flowing.

If ever your plant produces only one branch (and yes, that can happen), let the new stem grow for 6 months or so, then cut off the tip again. You sometimes need to prune more than once to force certain recalcitrant plants to grow multiple branches.

The other possibility would be to root the top of the plant when you cut it off (again, spray the wound with water to stop its sap from “bleeding”) and plant the rooted cutting in the same pot as the mother plant. If you do this 2 or 3 times, that will give you a dense cluster of branches that will look good even if your plant really isn’t doing much branching.

Try It On Other Plants

And removing the top of most other plants with an upright growth habit will have the same effect. Cut back the top growth of any plant capable of forming branches (palms don’t for example) and the plant will soon produce new shoots lower down.

Crown of Thorns: The Subversive Easter Plant

Standard

You’re just not into Easter? The idea of filling your home with perfumed flowers to celebrate a Christian version of an old pagan festival just doesn’t appeal to you? You’re deep into religious denial? Perhaps you can express your utter distaste with a plant that is all Easter, yet not so soft and cuddly as a lily or a daffodil, a sort of gothic Easter plant, if you like: the crown of thorns (Euphorbia milii). It’s much like keeping a rat as a sign of your reject of society … only easier to keep and less likely to escape.

The plant bears the name crown of thorns well: it is truly nasty! Seriously spiky thorns cover its branches and you’d be more tempted to handle it with a bottle holder than with your bare hands. Yet, subversively, it bears stunning blooms that certainly catch the eye.

The common name refers, of course, to the woven crown of thorns placed on the head of Jesus before his crucifixion (thus strongly linking the plant to Easter). No one knows which thorny plant was actually used for this purpose, but many plants (Paliurus spina-christiGundelia tournefortiiKoeberlinia spinosa, etc.) have picked up the common name crown of thorns as a result. 

Well grown plants can bear dozens of flowers for months at a time. Photo: Anneli Salo, Wikimedia Commons.

The best known crown of thorns plant is the one discussed here: Euphorbia milii, a popular succulent houseplant in colder climates (hardiness zones 1–8) and a common outdoor shrub in arid tropical climates (zones 9–12). You may also know it as Christ plant or Christ thorn. 

In spite of these names, it was probably not the plant actually used to make Jesus’s crown of thorns, as it comes from Madagascar, not Israel, although there is some historical evidence suggesting in may have been introduced to the Middle East at just about the right time. 

The crown of thorn’s botanical name Euphorbia honors Euphorbus, Greek doctor to the King of Mauretania around the time of Christ. The epithet milii honors Baron Milius, who is said to have introduced this species to cultivation in France in 1821.

Description

A mixture of colors of both regular and giant crown of thorns. Photo: http://www.worldofsucculents.com

The crown of thorns is a branching shrub up to 1.8 m (6 ft) tall (usually much smaller when grown as a houseplant) with extremely spiny gray stems. The broad oval fleshy leaves are mostly carried on new growth, leaving the lower stems bare. It’s usually grown for its attractive blooms, composed of two (sometimes more) colorful petal-like bracts that can last for months. The actual flowers in the center of the inflorescence are small and inconspicuous. The bracts are typically red or, more rarely, yellow in the wild, but there are all sorts of cultivars in a wide range of colors in culture—white, cream, pink, orange, bicolor, etc.—as well as dwarf varieties and cultivars with variegated foliage.

One of the many giant crown of thorn hybrids (Euphorbia lomi) with thick stems and larger flowers. Photo Ram-Man, gardensoline.com.au

There is also a common hybrid species with much larger flowers and leaves and a considerably thicker stem: E. lomi (E. milii E. lophogona). It’s sometimes called giant crown of thorns. Its blooms are particularly striking and come in an equally wide range of colors. The Somona hybrids are a group of cultivars from California with especially nice blooms while there is a horde of Thai hybrids often called Poysean hybrids, Poysean being the Thai word for I. milii. It’s generally less branching than the straight species and a bit of pruning may be needed to encourage it to produce more than one stem. 

When a crown of thorns is given good conditions, it can bloom at any time of year, although mostly in spring or summer. Some of the better cultivars will, if given top care, flower non-stop all year long. Under harsh conditions, notably extreme dryness, the crown of thorns may actually go dormant and not only stop flowering, but lose all of its leaves. When watered again, though, it will slowly come “back to life.” (Yes, a truly verifiable case of resurrection!)

The sticky sap of the crown of thorns is a toxic white latex. Don’t eat it and keep it out of your eyes and off your skin. Obviously, when working with this plant, it’s best to wear safety goggles and gloves. And keep this plant away from kids and pets!

Growing Crown of Thorns

Euphorbia milii ‘Variegated’ is a charming cultivar. Photo: tom-piergrossi.squarespace.com

It’s a very adaptable plant, but prefers full sun and well-drained soil. In hot climates, some protection from the midday sun is best. Although highly drought tolerant, it will nonetheless bloom best when kept moderately moist by regular watering. It will grow in just about any soil, from standard potting mixes indoors to poor rocky or sandy soils outdoors. It seems to get along fine with very little fertilizer, but you can apply some lightly during its main growing season, usually from early spring to early fall.

In dry tropical climates, it’s sometimes grown as a defensive hedge or to keep cattle out of fields. Certainly, cows won’t eat it, nor will deer or rabbits.

One thing the crown of thorns will not tolerate is cold. Even temperatures approaching freezing (35˚F/2˚C) can kill it. It’s best not to expose it to temperatures lower than 50 °F (10 °C).

The More the Nastier

You want to multiply your crown of thorns? You can theoretically grow it from seed, but that’s a slow and difficult process and germination is often poor. Plus, seedlings will likely not be like the mother plant. And good seed is hard to find! Be especially wary of web sites selling you multicolor crown of thorn seeds: they’re almost certainly scams.

Crown of thorns roots slowly but surely from stem cuttings. Photo: Nature Favour, http://www.youtube.com

However, you can readily grow crown of thorns from stem cuttings, best taken in spring or, failing that, summer. Water the plant a few days ahead so its stems are well hydrated.

Euphorbias of all kinds, including this one, tend to “bleed” white sap for a while after you cut them. This is not only alarming, but it weakens the cutting. To staunch the wound, spray it with cold water: this causes the sap to coagulate.

Next, apply rooting hormone to the wound (as the name suggests, it helps promote rooting) and insert it into a pot of barely moist soil. In fact, for a fuller final appearance, place three or more cuttings in each pot.  

Place the cuttings in a warm spot. They’ll need only moderate light and very little watering at first. When you see new growth appear, give them full sun and water more thoroughly to bring them into bloom.

Finding a Specimen

Crown of thorns. Photo: worldoffloweringplants.com

I don’t think you’ll have any trouble finding standard red crown of thorns plants: they’re widely available and sold in most garden centers. If you’re looking for special cultivars in a wider range of colors, though, you may need to find an on-line succulent nursery in your country. 


Crown of thorns: possibly the most irreverent Easter plant of all! And yet, behind those nastily spiny stems, it’s a charmer and certainly one of the easiest houseplants to get to bloom!

Cactus or Euphorbia?

Standard

If you grow cactus and other succulents, you probably have a few euphorbias mixed in with the cacti. Source: mashtalegypt.com, montage: laidbackgardener.blog

In the world of succulents, that is, plants that store water in thickened stems or leaves in order to better cope with arid conditions, two different families are often mistaken one for the other: cacti (Cactaceae) and euphorbias (Euphorbiaceae, genus Euphorbia). In fact, many people simply call all succulent euphorbias “cacti,” not realizing there is a difference.

Both cacti and euphorbias tend to be stem succulents, that is, they store moisture in swollen stems, both tend to very spiny and both include a variety of species of all different shapes. They are so similar in many aspects that confusion is understandable, yet they are no more closely related to each other than dogs are to cats.

Dogs and cats are both mammals, are covered in hair, have tails and pointy teeth and are carnivores, yet few people would confuse a dog with a cat. If you’re a gardener, you really should learn to tell a euphorbia from a cactus. Once you know the difference, you’ll never confuse them again.

Convergent Evolution

20180919B ENG www.kajuard-plantes.com & www.uhlig-kakteen.de

As a result of convergent evolution, many cacti and euphorbias have evolved to resemble one another. Source: www.kajuard-plantes.com & http://www.uhlig-kakteen.de

The similar appearance of cacti to euphorbias is an example of convergent evolution: the two different families evolved under similar conditions—under extreme aridity—and adopted similar survival tactics, resulting a lot of similarities. Even so, they also have their differences.

Telling the Two Apart

Here are a few tips on telling the euphorbias from cacti. You may well find you’re growing both of them without knowing it!

Echinopsis Candicans

A cushiony areole, with or without spines, is a sure sign of a true cactus. Source: http://www.krypton.ovh

  1. Cacti have areoles. These are cushiony, fuzzy dots from which spines, stems and flowers grow. They can be white or yellow, but are present on all cacti. No other plant has areoles. So, if you look closely at any cactus-like plant and see no areoles, as will be the case with euphorbias, that plant is definitely not a cactus! This is, hands down, the easiest way of telling the two apart. Once you know this, you’ll never confuse a cactus with any other plant again!

    20180919D Hernán Conejeros, YouTube.ca & Elton Roberts, xerophilia.ro .jpg

    Euphorbia thorns, usually single or paired, are part of the stem and hard to remove. Cactus spines often form a circle and are easily broken off. Source: Hernán Conejeros, YouTube.ca & Elton Roberts, xerophilia.ro

  2. Euphorbias usually bear single or paired thorns (modified stems), if indeed they have thorns. They’re usually thick and are clearly part of the stem: you can’t break them off without wounding the plant. Cactus have spines (modified leaves) rather than thorns. They often form a circle, although not always, and there may also be longer spines in the circle’s center. However, no matter how they are grouped together, cactus spines always arise from those cushiony areoles mentioned above. They can be snapped off very readily and indeed, some are designed to break off and penetrate the skin of animals to dissuade them from chomping on the cactus. Note that there are both thornless euphorbias and spineless cacti, so the absence or presence of prickles is not necessarily a factor in distinguishing between the two.

    20180919D Norman E. Rees, USDA ARS.jpg

    Euphorbias produce milky white sap, cacti rarely do. Source:Norman E. Rees, USDA ARS

  3. Euphorbias produce milky sap if you wound them. This is a sticky latex, often toxic or irritating to the skin, and almost always white (there is just one species with yellow sap, E. adbelkuri). Most cacti have clear sap, rarely irritating to skin, although there are a very few cacti with white sap, including a few Mammillaria.

    20180919E Florence Rogers, Nevada Public Radio & www.backyardnature.net .jpg

    Cactus flowers are highly varied and usually colorful. The true flower of the euphorbia above is the center and is unremarkable; it is only made attractive by the bracts that surround it. Source: Florence Rogers, Nevada Public Radio & http://www.backyardnature.net

  4. Cactus flowers are usually showy and colorful, with typical flower parts, including petals and many stamens. Take a look at how they are placed on the plant: they always grow from a cushiony areole. Euphorbia flowers tend to be small and yellow, have no petals and are usually quite insignificant, although in some species, such as the crown of thorns (E. milii), they are surrounded by modified leaves called bracts that can be quite colorful. They never grow from areoles.
*Be aware that unscrupulous cactus growers often stick fake flowers on cactus with glue guns. If the flower on a cactus does not grow from an areole and has a glob of glue underneath, you’ve been had!

20180919F E. Trigona www.plantandpot.nz

Many euphorbias, like this Euphorbia trigona, have leaves. Few cactus do. Source: www.plantandpot.nz

  1. Cacti are almost always leafless, at least as adults (all bear two cotyledons at germination). There are only a few exceptions (Pereskia, which actually don’t look like cactus at all, and a few Opuntia, for example). On the other hand, many euphorbias with succulent stems nevertheless bear leaves.
  2. Cacti evolved in the New World and are found in North, South and Central America as well as in the Caribbean. (There is only one species, Rhipsalis baccifera, that is native to the Old World.) Succulent euphorbias evolved in the Old World, mostly Africa, Madagascar and drier areas of Asia. In the wild, both are still mostly found in their native lands, although some cacti, notably in the genus Opuntia, have escaped from culture to become weeds in other parts of the world.

    20180910G lonelyplant_ph, deskgram.net & www.ebay.co.uk.jpg

    All these euphorbias are in the single genus Euphorbia, but the cactus shown are in various genera, including Mammillaria, Trichocereus, Astrophytum, Opuntia and Cereus. Source: lonelyplant_ph, deskgram.net & http://www.ebay.co.uk

  3. Euphorbia is just one genus in the family Euphorbiaceae. They are often called spurges. There are more than 2,000 species of Euphorbia, including such popular houseplants as mottled spurge (Euphorbia lactea), pencil tree (E. tirucalli) and crown of thorns (E. milii). Cacti are a family, the Cactaceae. The family also contains about 2,000 species, but is divided into about 175 genera, including Opuntia, Echinocactus, Mammillaria and Cereus.

There you go! It isn’t all that hard to tell euphorbias from cacti. Just the lack of an areole on euphorbias should be such an obvious difference that you’ll never confuse the two again!

50 Houseplants That Don’t Mind Dry Air

Standard

20171227A pexels.com .jpg

Most houseplants just don’t do well in desert-dry air! Source: pexels.com

Dry air is a major problem for houseplants in the winter… and indeed, any indoor plant (seedlings, cuttings, etc.). When the atmospheric humidity is less than 40%, certainly common enough in many homes, plants try hard to compensate by transpiring more heavily, that is, by releasing water to the air through their stomata (breathing pores). The drier the air, the more they transpire, and that can lead to their tissues losing water more rapidly than their roots can replace it. This can result in all sorts of symptoms of stress: wilting, flower buds turning brown, leaves curling under, brown leaf tips, even the death of the plant.

And if that weren’t enough, leaves stressed by dry air are also more subject to pest damage (red spider mites, whiteflies, thrips, etc.)

Some Plants Can Cope

201712257B davisla.wordpress.com..jpg

Plants with thick, waxy leaves cope better with dry air than those with thin ones. Source: davisla.wordpress.com.

That said, many plants, especially those native to arid climates or ones where they are exposed to long periods of drought, have developed ways of compensating for dry air. Cacti and succulents are usually very resistant to dry air and so are some epiphytic plants, like hoyas.

Some plants resist dry air by producing leaves with fewer stomata than normal, thus reducing water loss. Many have abandoned leaves altogether and breathe through their green stems (many cacti, for example). Others keep their stomata closed during the day, when the sun is hottest and water loss is greatest, breathing only a night. (This is called Crassulacean acid metabolism or CAM.) In other words, they essentially hold their breath 12 hours a day! Also, plants resistant to dry air often have extra-thick leaves or leaves coated with wax, powder or hair, all of which reduce evaporation.

Plants That Don’t Mind Dry Air

What follows are a few houseplants that don’t really mind it if the air in your home is on the dry side. Not that they will suffer if you increase the humidity to levels more acceptable to plants in general (most plants prefer a relative humidity of 50% or above) and that indeed is good for your health too, but if improving the atmospheric humidity something you just can’t do, at least these plants will pull through without a complaint!

20171227C Aeonium arboreum 'Atropurpureum' Bernard Dupont, WC.jpg

Aeonium arboreum ‘Atropurpureum’: one example of a plant that tolerates dry air. Source, Bernard Dupont, Wikimedia Commons

  1. Aeonium spp. (tree houseleek)
  2. Agave spp. (century plant)
  3. Aglaonema spp. (Chinese evergreen)
  4. Aloe spp. (aloe)
  5. Ananas comosus (pineapple plant)
  6. Aspidistra elatior (cast iron plant)
  7. Beaucarnea recurvata (ponytail palm)
  8. Cephalocereus senilis (old man cactus)
  9. Cereus peruvianus (Peruvian apple cactus)
  10. Ceropegia woodii (rosary vine)
  11. Clivia miniata (clivia)
  12. Crassula ovata (jade plant)
  13. Crassula spp. (crassula)
  14. Cryptanthus spp. (earth star)

    20171227 Dieffenbachia seguine Forest & Kim Starr, WC.jpg

    The thick leaves of the dieffenbachia can generally cope quite well with drier air, but you can see just a bit of damage at the tip of this one. Source: Forest & Kim Starr, Wikimedia Commons

  15. Dieffenbachia spp. (dumbcane)
  16. Echeveria spp. (echeveria)
  17. Echinocactus grusonii (golden ball cactus)
  18. Epipremnum aureum (pothos, devil’s ivy)
  19. × Epicactus (orchid cactus)
  20. Euphorbia lactea (candelabra spurge)
  21. Euphorbia milii (crown of thorns)
  22. Euphorbia tirucalli (pencil cactus)
  23. Ficus elastica (rubber tree)
  24. Ficus lyrata (fiddle leaf fig)
  25. Gasteria spp. (ox tongue)
  26. Gymnocalycium mihanovichii friedrichii ‘Hibotan’ (red ball cactus)
  27. Haworthia spp. (zebra plant)
  28. Hippeastrum cvs (amaryllis)
  29. Hoya carnosa (wax plant)
  30. Kalanchoe (kalanchoe, panda plant)
  31. Ledebouria socialis (silver squill)

    20171227E Dysmorodrepanis, WC.jpg

    Few plants tolerate dry air as well as living stones (Lithops). Source: Dysmorodrepanis, Wikimedia Commons

  32. Lithops spp. (living stone)
  33. Mammillaria spp. (pincushion cactus)
  34. Opuntia spp. (bunny ears)
  35. Pachypodium lamerei (Madagascar palm)
  36. Pelargonium graveolens (rose-scented geranium)
  37. Pelargonium × hortorum (zonal pelargonium, zonal geranium)
  38. Peperomia obtusifolia, P. clusiifolia (baby rubber plant)
  39. Philodendron hederaceum oxycardium (heartleaf philodendron)
  40. Rhipsalis spp. (mistletoe cactus)
  41. Sansevieria trifasciata (snake plant)
  42. Schlumbergera (Christmas cactus)
  43. Sedum spp. (sedum, donkey’s tail)

    20171227F Senecio rowleyanus Forest & Kim Starr, WC.jpg

    The nearly round leaves of Senecio rowleyanus are designed to reduce evapotranspiration. Source: Forest & Kim Starr, flickr

  44. Senecio rowleyanus (string-of-pearls)
  45. Senecio serpens (blue chalksticks)
  46. Stapelia spp. (carrion flower)
  47. Streltizia reginae (bird of paradise)
  48. Syngonium spp. (arrowhead vine)
  49. Yucca elephantipes (spineless yucca)
  50. Zamioculcas zamiifolia (zeezee plant)20171227A pexels.com