Top Tips & Info
- Care Difficulty - Easy
- Provide a bright location with around a few hours of sunlight per day. Recently purchased specimens must build up their tolerance and exposure to the sun over the course of the next eight weeks to avoid sun-scorch.
- Fertilise every two or three months using either a 'Cactus' or 'Houseplant' labelled feed.
- Repot every three years during the spring, using a 'Cactus & Succulent' labelled potting mix. If you're interested in producing a show of blooms, keep the specimen pot bound to restrict the root system. Scroll down to 'Flowers' for more information on this.
- Keep an eye out for Spider Mites, Mealybugs & Scale that'll hide in the plant's cubbyholes.
Location & Light
As mentioned above, Crown of Thorns are best located in a bright location with a splash of morning or evening sun. The warmth and light from the sun will considerably increase the chance of summer blooms, as areas with near-constant temperatures all year round will stunt the specimen's growth. A few hours of off-peak sunlight will be highly beneficial for the plant, as it’ll significantly reduce the risk of over-watering and root rot. Due to the species' intolerance to low light, avoid placing one in areas where a newspaper can’t be read without the use of artificial light.
Not only will continuous soil moisture ruin their root systems, but it'll also increase the risk of a rotten stem which essentially will destroy the plant. Allow all of the soil to thoroughly dry out in between waters in the growing period, reducing this further in the autumn and winter. Under-watering symptoms include a shrivelled stem, yellowing leaves, little to no growth and dry, crispy patches forming on the leaf edges. These issues are usually caused by too much light/heat or forgetfulness. Remember, the brighter the location, the more watering you'll need to do. Over-watering symptoms include a weakened or rotten stem, no new growth, yellowing lower leaves and eventual plant death. The differences between under and over-watering can be very similar, with a rotten root ball or stem being the obvious difference.
This is not a necessity; however, a quick hose down from time to time will hydrate the leaves and wash away dust or potential pests.
Fertilise every two months during the growing period and every three months in the autumn & winter to replicate its dormancy period. Although a 'Houseplant' fertiliser will still do the job, we'd recommend using a specific 'Cactus' labelled feed as it'll support the vital thirteen nutrients that this species will need to grow.
Common Issues with Crown of Thorns
Curled leaves and dried brown edges are the result of too little water and over-exposure to the sun. Although Crown of Thorns can naturally do well in sun-filled locations, those that haven't acclimatised to the harsh rays will show signs of sun-scorch and environmental shock. Prolonged exposure will significantly speed the process of dehydration, so consider transplantation into a bigger pot in the spring to wrap the roots around moister soil.
Root rot is a common issue with specimens sat in too moist or waterlogged soil for long periods. Symptoms include rapidly yellowing leaves, stunted growth and a rotten brown caudex. Take the plant out of the pot and inspect health below the soil line. If the roots sport a yellow tinge, you're good to go, but if they're brown and mushy, action must be taken immediately.
Directly pinpointing yellow leaves is rather hard due to the many different issues that could be at fault. Problems include watering-related abuse, too much or too little light, and fertilisation issues.
Never allow temperatures to dip below 12ºC (54ºF) as irreversible damage may occur in the likes of yellowed foliage and weakened growth. If this happens, remove the severely affected areas and immediately improve growing conditions - never cut through softened yellow growth, and only around brown, crispy squares. As rehabilitation can take several months because of its slow-growing nature, be sure to provide a stable location with better growing conditions to speed this process.
A lack of flowers is caused by an insufficient dormancy period, where the temperatures are kept more or less the same over the year. Reduce the warmth by a couple of degrees over the autumn and winter, along with fewer irrigations to ensure a well-spent dormancy. As spring arrives, the natural temperature will begin to increase, with this is being the perfect time to increase waters and fertilisation. Remember, the warmer the summer days are, the more likely a specimen is to reflower.
Charles des Moulins first documented Euphorbia milii during a trip to its homeland of Madagascar in 1826. He commemorated Baron Milius, a previous Governor of the Réunion Islands who brought the species to France five years previously. According to ancient documents, this species was one of the first to be introduced to the Middle East, and one that is associated with Jesus Christ's Crown of Thorns.
12° - 32℃ (54° - 90℉)
H1b (Hardiness Zone 12) - Can be grown outdoors during the spring and summer in a sheltered location whilst night time temperatures are above 12℃ (54℉), but is fine to remain indoors, too. If you decide to bring this plant outdoors, don't allow it to endure more than an hour of direct sunlight a day as it may result in sun-scorch. Regularly keep an eye out for pests, especially when re-introducing it back indoors.
The overall size can be up to 1.4m in height and 0.8 m in width. The ultimate size will take between 10 - 15 years to achieve when re-potted every few years, with several new leaves unfurling per annum.
Pruning & Maintenance
Remove yellow or dying leaves, and plant debris to encourage better-growing conditions. While pruning, always use clean scissors or shears to reduce the chance of bacterial and fungal diseases. Never cut through yellowed tissue as this may cause further damage in the likes of diseases or bacterial infections. Remember to make clean incisions as too-damaged wounds may shock the plant, causing weakened growth and a decline in health. Deadhead the flowers as they spend to improve the overall bloom time.
Via Seed or Stem Tip Cuttings.
Stem Tip Cuttings (Easy to Moderate) - This method is an easy way to duplicate the original plant. Stems that are at least 8cm (3 inches) in height and part of an established plant are most successful. To avoid making a mess of the serrations, use a clean pair of scissors and cut 8cm down from the stem's end, dipping the wound in water and then into rooting hormone to speed the propagation. Rooting can take in the range of between two to eight weeks, depending on environmental factors and the cutting's quality. We recommend using a 'Cactus & Succulent' labelled potting mix, with a pot that has adequate drainage to avert the risk of blackleg. Provide a bright, warm setting of around 20℃ (66℉) with relatively moist soil, but be sure to allow the top half to dry out in between waters. You'll know if propagation is successful as the leaves will stay green and firm, along with small roots developing from the callous (dried wound). New foliar growth will emerge from the nodes after around twelve weeks, but it may take longer if the conditions aren't optimal. After a month of solid new growth, transplant into a slightly bigger pot and treat it like a mature specimen with the care tips provided above.
Crown of Thorns will flower between late spring to late summer, producing small disk-like flowers across the foliage line. Each inflorescence can last up to two weeks, with the overall flowering process spread across several weeks.
To achieve a bloom, you must provide a cool and dry dormancy period. From the end of autumn to early spring, water infrequently to avert the risk of over-watering and remember to present a location with a few hours of direct sunlight per day. The ideal temperature should gently fluctuate between the day and night around 14 - 17℃ (52 - 62℉) to provide an efficient resting period. From mid-spring onwards, the natural temperature will begin to increase, with more frequent waters and fertilisation taking place. Remember to use a potassium-based fertiliser, for example, 'Tomato' food, to maximise the chance of a bloom. If all is successful, you'll potentially see small buds develop across the nodes of the foliage in the height of summer, lasting up to a month.
Repot every three to four years in the spring using a 'Cactus & Succulent' labelled potting mix and the next sized pot with adequate drainage. Crown of Thorns are far better potbound for several years due to the heightened risk of root rot and repotting-issues (like transplant shock) - so only repot if you feel it's wholly necessary.
Hydrate the plant 24hrs before tinkering with the roots to prevent the risk of transplant shock. For those situated in a darker location, introduce extra amounts of perlite and grit into the lower portion of the new soil to downplay over-watering risks.
Pests & Diseases
Keep an eye out for mealybugs, spider mites, scale, thrips, whitefly & root mealybugs that'll locate themselves in the cubbyholes and undersides of the leaves, with the exception of the latter in soil. Common diseases associated with Crown of Thorns are root rot, leaf-spot disease, botrytis, rust, powdery mildew & southern blight.
This plant is classified as poisonous; if parts of the plants are eaten, vomiting, nausea and a loss of appetite could occur. Consumption of large quantities must be dealt with quickly; acquire medical assistance for further information. The sap can also cause dermatitis and skin allergy to sensitive individuals, so be sure to wear gloves when handling.