Cacti and other succulents (succulents) are currently very fashionable. We see them more and more in chic boutiques, often in expensive individual pots or suspended in kokedamas (Japanese foam balls), but also in glass-walled containers. In other words, in terrariums. But this last use almost always leads to the death of succulents.
Their death occurs more quickly in closed terrariums, that is to say with a glazed lid, but even in open terrariums, the plants also die.
What is going on?
An environment that does not suit them
To truly succeed in the long run, the majority of succulents need full sun and a substrate that dries thoroughly before the next watering. And that’s not all: they also need good air circulation and a not too humid atmosphere. None of this is possible in a terrarium.
Growing succulents in a terrarium exposed to natural light is the equivalent of wanting to raise goldfish in a sandbox, the only difference being that goldfish die instantly while succulents often die very, very slowly .
If you place a container with glass walls in full summer sun, the heat will increase excessively. At 40?C or 50?C, even more. This is called the greenhouse effect. Okay, summer temperatures are also becoming extreme in desert areas where some (but not all) succulents grow, but then there is good air circulation and also the temperature drops at night, giving plants a break. . Not in a terrarium.
To avoid this, sellers of succulent terrariums recommend placing them in a “well lit, but sheltered from direct sunlight” location. That avoids overheating, but then, it leaves the plants hungry because light – their only source of energy – is too weak to stimulate normal growth.
When you grow a succulent, usually a full sun plant, in the shade, usually it shows no sign of distress at first. It remains pretty good. So, his owner thinks that everything is fine and is quite surprised when, 6 months, 9 months, 1 year later, the plant begins to rot or wither . Some succulents are more able to tolerate low light than others (gasterias, rhipsalis and some haworthias, for example), and so they survive longer. True desert cacti, on the other hand, are usually the first to decay.
Under artificial lighting
However, a terrarium can be well illuminated under intense artificial lighting that emits little heat, such as a 4-tube fluorescent lamp (a 2-tube lamp may be sufficient for partial-shade succulents). Thus they are given the strong luminosity necessary for their blossoming without having to fear that they will become leathery. However, it is sometimes difficult to arrange such intense lamps to an interior decor. A good reflector that directs the light to the plants and not to the eyes will surely be needed.
Also, this use does not correct the problems of excess water and too high humidity.
Too much water … in the soil as in the air
It is terribly difficult to water a terrarium. There is no hole in the bottom of the container to let out excess water: a spoonful too much and the plants are in a medium overloaded with water. And succulents do not like their roots soaking in water.
But the stylists who prepare the terrariums (I can hardly call them horticulturists!) Inevitably include a “drainage layer” of gravel at the bottom of the terrarium. Is not that the surplus of water will go there?
In fact, however, the so-called drainage layer at the bottom of a terrarium has never worked. True terrarium experts (those who keep their terrariums for years, not the stylists who make up beautiful mounts for sale, but who never see the results of their mess) never put them: they know it is useless. Because there is little space for roots in a terrarium and inevitably the roots of plants, succulent or not, end up soaking in water. And anyway, this stagnant water will rise in the soil above by capillarity, keeping it still moist.
In a more airy container, like a classic flowerpot, this kind of excess water flows through the drainage hole and any excess remaining evaporates quickly, but in a terrarium none of this happens. The air remains very humid and stagnant (besides, another situation that succulents hate) and evaporation is slow (open terrarium) or zero (closed terrarium).
A question of compatibility
Added to this is the fact that the stylists who make up the terrariums never seem to take into account the compatibility of the plants. They often place plants that have very different needs in the same terrarium, such as a cactus that prefers a cold and very dry winter with a succulent that likes its winters rather hot and is not disturbed by a little moisture. Or a plant that has a very clear growth arrest (dormancy) with a plant that continues to grow year-round.
Another aspect of compatibility in a terrarium is the eventual size of the included plants. Stylists pay no attention to what plants in a terrarium can look like at maturity. They are content to create a beautiful temporary arrangement. After all, it is unlikely that the plants in the terrariums they prepare will survive long enough to grow! But if ever, by a miracle, the terrarium you bought finds an environment conducive to the survival of the plants it contains, you will discover that many of the succulents included are not miniatures, but young cuttings of giant plants that will choke the plants. other plants by their overflowing growth.
Terrarium with a single plant
Often a mini-terrarium containing a single plant is easier to manage than a mixed terrarium. On the other hand, all that remains is to find a place where even a succulent in an individual terrarium can receive a light intense enough for its blossoming without it bursting with heat remains always a problem and that this does not solve no plus the problems of excess water and too much atmospheric moisture.
In other words
Terrariums of succulents sold on the market are designed for the beauty of their assembly and their ability to remain attractive during the sales period. The long-term viability of editing is rarely taken into consideration.
If you want to buy one to decorate your home for several months, go ahead. When the plants begin to die, probably the seller will be ready to make a new assembly, for a fee, of course. But it’s sad to see all these plants finish with compost.
More and more, we see terrariums that contain succulent plastic. No maintenance is necessary, except dusting, and you can place them anywhere, in full sun as in the most shady corner! This may be the best solution for non-gardeners.
But if you like to cultivate plants, keep them alive, see them flourish, it is better to grow cactus and succulent in individual pots or in a “cactus garden”, a large pot without glass walls and equipped with drainage holes, with congeners with the same cultural needs.