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Cacti – A prickly matter


Everyone knows that roses have thorns and cacti have spikes, right? What may be common in everyday language, is seen by botanists quite differently: for them, a thorn is a leaf or a branch - just like cacti. A sting is a sharp cusp on a leaf or on a branch - just like roses. So the other way round to what is colloquially thought of.


What actually are cacti?

Cacti are mostly succulent plants, but not all succulent plants are cacti. Succulent plants have thickened trunk, leaves and tissues and even a water reservoir, all so that they can survive without water. With the discovery of America, the first cacti were discovered by Europeans, its distribution was originally limited to the native Americans.

It's a slow process

Almost all cacti grow relatively slowly, the exception being the leafy cacti (formerly phyllocactus), which include the Christmas and Easter cacti. Leaf cacti are also succulents (leafy succulents), but grow fast, have only a relatively short rest period and need less light than their relatives. That's why they are well suited for the bedroom window.

Cacti cannot do without light

All other cactuses, however, need a lot of light, as only then can they achieve their typical growth patterns. A lack of light, e.g. in indoor settings, they become long and soft. On the other hand, many cacti protect themselves from too much light with their spherical shapes, which creates a relatively small surface with the same volume. As a result, cacti have a so-called evaporation protection feature in-built. Additionally, a dense wool or thorn dress can protect them against intense sunshine. But, even cacti can burn.

Many cacti, such as the Opuntia (prickly pear), can even be planted out in the garden. Cacti in extreme drought have developed the ability to avoid water loss by shrinking almost completely and sometimes even resort to retreating underground. Such species often have turnip-like thickened roots in which they can store additional water.

Cacti as prey

The thorns of a cacti are intended to protect them from predators - because wherever cacti grow, green fodder is often scarce. Another protection mechanisms which cacti use is known as glochids, the prickly pear is known for using these. Glochids are hairy thorns which grow in small clumps. They have small barbs and are easily detached from the plant. When handling them, e.g. when repotting, this protection can also be unpleasant for an unlucky gardener. With a simple trick - using the warm, soft wax of a candle - the thorns can easily be removed from the skin.

Cacti blooms

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Blooms from big to small

Many cacti grown indoors rarely or never bloom, simply because they lack enough light. Here, cacti, depending on the species, flower up to 30 cm in diameter. But there are also the tiny flower varieties. Among them are day and night blooms, with many different colours, from bright vermillion to pale green. Most of the flowers appear in circular formations and they can also smell. These are pollinated by insects, bats and hummingbirds. In addition to the flowers, the fruiting bodies (seeds) of many cacti are very attractive. Despite the risk they pose to some birds, they are eaten anyway and the seeds are then distributed unwittingly.

Even the slow-growing cactus needs fertiliser. You should use a special fertiliser or a significantly lower dosage of complete fertiliser. A complete fertiliser contains the main nutrients with any required trace elements. Fertilisation takes place usually towards the end of July and it is possible to fertilise with a phosphorus fertiliser (flower fertiliser). From August onwards, most cacti will begin to mature. Watering should then be slowly reduced and allow the cacti to have a rest period. They must be kept in a cool, dry and bright place during the winter, otherwise they will lose their shape and become distressed. Cacti are only sown between March and November. Any irrigation water should be as soft as possible, the most optimal is rainwater.

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False flowers in cacti

Some may ponder whether the flowers of some cacti in a garden center are real. But they are actually real flowers, they are just not from the cacti themselves. These are "straw flowers" which were stuck on. Even more confusing are red and yellow cacti sold as "strawberry cacti" (see picture) or "banana cacti". These are true, but not only viable, chlorophyllous mutants that are grafted onto "green" substrates. Many varieties of fruit trees are also propagated in this way. This "grafting" is a form of vegetative propagation. In cacti, low-growth varieties are grafted onto fast growing ones. In this way even the popular "cristata" (with strains or deformations on its trunk) can be preserved, because even they grow only extremely slowly or are not viable.

Repot cacti safely

The substrates for cacti and succulents often consist of coarse sands, loam and small amounts of compost. You should not use normal potting soil. Cacti only need to be repotted every 2-3 years. However, if newly purchased plants are in conventional peat, they should be repotted immediately. With old, large pots, it is often sufficient to exchange only part of the earth for fresh cactus soil. Cacti with turnip roots need narrow, deep pots; whereas cacti with finer roots prefer flat, wide containers. The best time to repot is at the end of the rest period from early March to May, before growth has properly begun again. Damaged roots should always be allowed to dry first.

By the way, you can easily protect yourself from the thorns using a simple folded newspaper.

The right accessories for planting and potting cacti can be found in our online shop.

The original version of this article was published in the greenhouse post, issue 03/2016, text and image: Jörn Pinske.

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