Why Don’t My Euphorbias Bloom?

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Yes, some euphorbias are very slow to bloom. Photo: hortology.co.uk & clipart-library.com, montage: laidbackgardener.blog

Question: I have a collection of succulents and most of them flower every year. But none of my euphorbias bloom. Why not?

Frustrated Succulentophile

Answer: Your lack of success getting euphorbias (Euphorbia spp.) to bloom is probably due to … your choosing the wrong plants! 

Among the 2000 or so species of euphorbia, there are some that bloom readily in the average home and others that will probably never bloom at all.

The crown of thorns (E milii) is easy to bloom. Photo: worldofsucculents.com

For example, the crown of thorns (E milii and its hybrid E. × lomi) is not hard to flower. In fact, it often blooms several months a year; under really good conditions, it will practically never be without some bloom.

Another that blooms readily is E. lophogona. In fact, it self-seeds in all the nearby pots in my plant room!

And what about the poinsettia, which is not a succulent, but is an euphorbia (E. pulcherimma)? As long as you give it short days in the fall, it will bloom faithfully at Christmas, at least in the northern hemisphere.

The baseball spurge (E. obesa) is another that blooms regularly, even if its flowers are relatively discreet.

Bigger Isn’t Better

Photos: plantsam.com & http://www.uhlig-kakteen.de

I suspect you’re growing some of the candelabra-type euphorbias, such as the African milk tree (E. trigona) and the milk spurge (E. lactea), two of the most popular indoor euphorbias.

Euphorbias that take this form, that of a small tree with an erect trunk and thick branches, are very slow to flower. You’re going to need a lot of patience—and space!—to see these bloom. Not only do they have a treelike shape, but they take on treelike dimensions. Often these species only flower at a very advanced age (20, 40 or 60 years old) or when the plant has reached a very large size -10 to 20 feet/3 to 6 m tall —, pretty much impossible to reach in the average home.

Also, be aware that, according to Wikipedia, the African milk tree (E. trigona) has never been known to bloom … and never is a very, very long time! (This plant is unknown in the wild and may be a hybrid; hybrids are often infertile or fail to bloom.)

Moreover, candelabra euphorbias are not the only candelabra succulents that are slow to flower. Most of the various candelabra cactuses (CereusAcanthocereusBrowningiaLophocereus, etc.) must also be large and fully mature to bloom. The famous saguaro cactus (Carnegia gigantea), with its big, thick arms, for example, has the reputation of not blooming before it reaches 75 years old!

The crested milk spurge (E. lactea cristata) is unlikely to bloom. Photo: vikisuzan, flickr.com.

Note too that crested succulents, that is, mutated ones with stems that grow in the form of a cock’s comb, are so severely deformed they are very likely to flower and several euphorbias have precisely this shape. That includes the very popular crested milk spurge (E. lactea cristata). I don’t know that it has every bloomed.

Euphorbias that are strongly variegated (marbled with albino tissue), too, can be very reluctant to bloom.

Best Conditions Possible

Of course, you still need to have the right conditions if you want to see any euphorbia bloom. Even a “euphorbia that blooms readily” needs a lot of light, even full sun, watering when the soil is dry, but not super dry, reasonable temperatures (very few enjoy cold winters), modest fertilization, etc. to be happy and only a “happy euphorbia” will flower.

But since you say that your other succulents are able to bloom, I suspect that you are giving your euphorbia adequate conditions. After all, euphorbias have about the same needs as a typical succulent.

So, my suggestion to you is to go out and buy a euphorbia specifically recognized for its ease of bloom. In fact, save yourself a lot of doubt and effort and buy it in bloom. And I don’t consider that cheating. Part of being a laidback gardener is always taking the easy way out! 

When a Red Euphorbia Turns Green

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The red African milk tree (Euphorbia trigona ‘Rubra’) is often burgundy red when you purchase it, then turns green under the lower light of your home. Source: http://www.ebay.com

Question: I bought a euphorbia as a houseplant. I chose it because it was dark red, but now the new shoots are green and it’s losing its red coloration. Does it need more sunlight? And how do I water it?

Nicole

Answer: The euphorbia you bought is probably Euphorbia trigona ‘Rubra’ (also sold as E. trigona rubra or E. trigona ‘Royal Red’), often called the red African milk tree because of its milky white sap and African origin. It’s a mutation of the normal form that has triangular green stems marbled with white and small green leaves. Exposed to intense sun, ‘Rubra’ produces a reddish stem and red leaves. This coloration tends to disappear in winter, even in summer when the plant is in too much shade. If it’s put back into the sun, the reddish color returns.

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Many other succulents redden in bright light, like the jade plant (Crassula ovata). Source: http://www.bonsaiempire.nl

20181209W Echeveria 'Black Prince' www.provenwinners.com & www.tissuecultureaustralia.com.jpg

Echeveria  “Black Prince” in summer (left) and winter (right). Source: http://www.tissuecultureaustralia.com.au & http://www.provenwinners.com

This euphorbia is not the only plant that reacts that way. Many other plants, especially succulents (aloes, echeverias, crassulas, rhipsalis, etc.), turn reddish in full sun, because the red pigmentation, caused by a buildup of anthocyanins, acts as a kind of sunscreen, protecting the stems and leaves against the harmful effects of the sun and especially its ultraviolet rays. Under lower light, the “sunscreen” is not needed and fades away, leaving a green plant.

 

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Pieris japonica ‘Mountain Fire’. The new leaves are bright red, but will turn green when they mature. Source: mikesgardentop5plants.wordpress.com

In many non-succulents, there is a similar situation, except it’s the fragile new leaves that are red at first, but then become a normal green color as they mature and harden off.

What to Do?

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This Euphorbia trigona ‘Rubra’ was red at first, started to turn green, then reddened up again when exposed to more intense light. Source: absolutely_fuzz, reddit.com

It is clear that your euphorbia is not getting enough sun for it to maintain its reddish color. Before you bought it, it was probably grown in a greenhouse, where providing intense sunshine is easy, but in the home, it really should be placed near a sunny window at all times. This is especially true in the winter, when the sun is much, much less intense. And for an even more intense coloring, grow it outdoors in full sun during the summer months.

As for watering, like most succulent euphorbias, the African milk tree is very tolerant of irregular watering. Ideally, you’d water abundantly, then allow the growing mix to dry thoroughly before watering again. The frequency of watering will vary according to the conditions and the seasons: you may need to water it weekly in hot summer weather, but only every two to three weeks under cooler, shadier winter conditions.

Cactus or Euphorbia?

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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!