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I purchased a cactus from IKEA. It appears to be Euphorbia Pentagona or Euphorbia Enopla. The date on its pot makes me think it was repotted on December 14 2016, 4 days before I purchased it. On the day of purchase, the soil was moist.

Since purchase, the cactus has been sitting close to a south-facing window, however the weather conditions in the Netherlands rarely lead to full-sun exposure in the winter months. Indoor temperatures have fluctuated between 14°C (57°F) and 18°C (64°F), while outdoor temperatures have ranged between -1°C (30°F) and 7°C (45°F).

One month after purchase, the top of the plant's stems show signs of bright green growth. My untrained eye is unable to distinguish whether this is etiolation.

The guides I read say that most cacti need a period of dormancy between November and March where they need water only once every one or two months, and no fertiliser.

Somewhat contradictory, guides also say that cacti prefer to be fed during spurs of active growth, such as the one I think my cactus is experiencing.

My questions:

  • Is this cactus etiolating (maybe due to the change in conditions), or growing?
  • Depending on the answer to the previous question, and keeping in mind that it's still winter, should I fertilise my cactus?
  • If I need to fertilise, is this 4-4-6 NPK cactus fertiliser solution that I purchased appropriate?

Pictures:

I've added before and after pictures for comparison below. You can notice the growth I'm referring to especially at the top of the bigger stem on the left:

December 18 2016:

December 18 2016

January 14 2017:

January 14 2017

  • 1
    Euphorbia is not a cactus. Different family. Just some forms of Euphorbia are succulent plants. – Giacomo Catenazzi Jan 14 '17 at 19:30
  • @Gabriele Cirulli.You're awesome. This post of yours is the most insightful and well-written question I have seen on this forum in a long time. Stick with us, learn, grow and contribute your knowledge young buck! I'm so impressed by your intrigue. – Brenn Jan 19 '17 at 4:36
  • PS. Giacomo is correct in that this plant is not a true "cactus" but your research still applies since it is a succulent and most cultural directions for cacti apply to all succulents, – Brenn Jan 19 '17 at 4:41
  • An update: as those who responded mentioned, the plant endured the little trauma and the hole callused over, without expanding. To this day it's still doing fine, and growing a little. I moved it to a new pot yesterday, fortunately without making any damage to it. – Gabriele Cirulli Feb 13 '17 at 13:36
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We say a plant is 'etiolated' when its growth becomes long and lanky, usually thin and weak looking, often yellowish or pale in colour, and with elongated gaps between leaves on stems, although this latter is not applicable to your particular plant.

Your plant (Euphorbia enopla gets my vote for ID) is looking very healthy. From what you say, you are keeping it in conditions that suit it well; despite the lack of regular sunlight, it is in bright daylight conditions, which is fine. If you're right about when it was repotted, the potting compost used will have contained some fertilizer, and I do not recommend you fertilize at this stage. Most houseplants do better being largely ignored, although watering as necessary shouldn't be neglected, so I suggest you leave it alone and just monitor its progress.

I don't know which resources you looked at for information on this plant, but I've found it quite difficult to find anything sensible about it as a houseplant, most information I found was regarding growing it outdoors in warmer countries, with very little detail about growing it indoors. I can't comment on whether the fertilizer you've purchased is appropriate for this plant, it doesn't sound like it would be harmful in any way, but bear in mind that 'less is more' so to speak. Many people never fertilize their plants, or may do so only once or twice in the growing season (depending on the product used), particularly for cacti, relying on occasional repotting to supply nutrients, and the plants do just fine. Just to reassure you, there's no evidence of etiolation in your plant currently, and I wouldn't expect any either, given its bright light situation.

  • Thanks a lot. Is it safe to assume that the new growth will reach the same diameter as the rest of the cactus without help? In the past I've had a cactus grow into an upside-down funnel shape, something I had interpreted as healthy growth initially, but turned out to be etiolation. Also, based on your advice, I think I'll hold out and fertilise this plant only around March, and then try to do it at most two or three times for the rest of the year. Is that a good idea? – Gabriele Cirulli Jan 14 '17 at 11:10
  • Yep, sounds good to me. I'm just irritated that I can't find any good information on this plant as a houseplant, such as whether it does better if stood outdoors during summer, but on a south west facing window sill, it will likely receive a fair bit of sunlight in summer anyway. Etiolation, by the way, is all about light levels and not about lack of fertilizer, and from the little info I've found, some morning or afternoon sun is perfectly adequate. Looking closely, yours looks like it might be going to produce flowers, but its hard to be sure... – Bamboo Jan 14 '17 at 11:28
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The fertilizer you have bought has a NPK ratio of 4-4-6 and this means it has more potassium than nitrogen and phosphorus. Higher levels of potassium than the other two are used to induce flowering, something that is useles when the plant should be dormant. Unused substances accumulate in the soil and lead to later disequilibrium.

  • Thanks. Do you have a suggestion as to the right kind of fertilizer to induce healthy growth in spring? I'll buy that instead. – Gabriele Cirulli Jan 14 '17 at 13:02
  • As Bamboo says, it may not need fertilization at all, not even in spring. These plants are adapted to growing with less nutrients. Not fertilizing them leads to slower growth, but longer life. Don't water again until it has sufficient light (spring). A friend of mine who has an entire collection of cacti transplants all her new aquisitions in winter because most of them come in peat that solidifies when dried and don't absorb water in spring when watered again. She uses store bought cacti soil and ads some extra sand to it. – Alina Jan 14 '17 at 13:54

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