Cactus e Dintorni

IMPORTANT: CACTUSES IN THE WINTERTIME

In the winter cactuses require a period of rest, when physiological activities are minimized, which is an evolutionary response to their extreme environment; this dramatic behaviour, in fact, allows them to survive the harsh climate of their natural habitats and therefore it is something we should know about and respect. During this kind of dormancy they should be kept in a cool place with very low humidity levels and not receive any water, though there are exceptions to this general rule as explained further below. In the spring we can resume the routine horticultural practices since the plants will have started growing again and with any luck they will prepare to flower.

Placing dormant cactuses indoors, on a window-sill for example, is not a wise choice. Instead it’s recommendable to move them to an unheated room such as a garage, attic or basement as well as a stairwell that need not be very bright as the plants are not growing. When this is impossible they might as well be overwintered on a balcony under some makeshift shelter from the cold and rain. On the contrary, if brought into a heated place they will not be allowed to go dormant and the new growth is likely to be unhealthily thin due to lack of light (etiolation). Moreover, if water is not applied the plants will wither and die as a consequence of the high transpiration. Many cactuses can withstand frost if given the protection of a conservatory where the temperature can rise significantly on sunny days; there’s also a group of plants, the so called “cold-hardy cacti”, comprising Austrocactus, Echinocereus, Escobaria, Opuntia, Pediocactus, Sclerocactus, Thephrocactus, Toumeya, Uthaia and a few others that can even survive harsh winters covered in snow as long as they’re not exposed to rain and humidity.

Preparations for the winter: September is the last month to apply insecticides or fertilizers. Watering should be suspended when the outside mean night temperature goes down to about 8°C (46°F). It is recommendable to install a ventilator in your glasshouse or conservatory to improve air circulation and keep humidity levels low thus preventing the proliferation of mildew and fungal diseases. It is also important to keep the room clean and disinfected, taking care to remove dead leaves, spent flower heads and ripe fruits. In addition, the place should not be crammed with pots if you want to avoid the spread of pests and diseases. Be also careful not to damage plants since pathogens are able to invade them through the wounds.

Plants can be roughly divided into four categories according to the environmental conditions that best suit them:
A – Very warm place - like a heated house - (= /above 57°F)
B – Cool to warm place (from 45/to 54°F),
C – Cool, unheated place (from 28/to 43°F),
D – Cold or outdoor place sheltered from the wet (=/ 27°F or lower).
The list comprises the most commonly cultivated species of cacti and other succulents. The temperatures shown must be regarded as approximate values since the tolerance of plants to cold conditions depends on a number of factors usually linked to one another, such as atmospheric humidity (the greater the humidity level, the higher the temperature required), the duration of exposure to the cold (many cacti can endure light, occasional frosts but not severe or prolonged ones), the health of the plant and its acclimatization to the local weather conditions and so on. When in doubt as to the ideal temperature, it’s better to keep it a few degrees higher than lower, especially for non-cactaceous succulents.

WINTER MINIMUMS

PLACE A (>= +14°C)

PLACE B (da +7 a +12°C)

 PLACE C (da -2 a +6°C)

 PLACE D (< = di -3°C)