Overwintering conditions in Poland

First divide the collection by its needs

Cacti differ in their dormancy. Some terrestrial plants tolerate a cool period with greatly reduced water. Tropical epiphytes and warmth-loving rootstocks require different care. A seedling has smaller reserves than a large stem, and a newly rooting cutting differs from an adult plant with functional roots. Grouping plants by these features is more useful than placing the entire Cactaceae family in one location. [Fleischer and Schütz 1978] [1-WWW] [1-WWW]

Before moving a plant, assess its condition, identification and the actual conditions in its future overwintering space. A plant with a wet root ball cannot readily be managed as safely as one that has gradually ended growth. Specimens with feeding damage or tissue breakdown need isolation and assessment. Cold does not replace plant protection. [Fleischer and Schütz 1978] [1-WWW] [1-WWW]

Comparing overwintering methods

[Fleischer and Schütz 1978] [1-WWW] [1-WWW] [1-WWW]

Ground and shelter from precipitation

Drainage must function throughout the root zone. Check where runoff from the surroundings goes, whether a poorly permeable layer lies beneath the bed and where snowmelt collects. Gravel top dressing alone does not solve a wet soil profile. Raising the bed helps only if water has a real drainage route. [4-WWW] [1-WWW] [Koski 2019]

A roof can limit precipitation but does not automatically ensure higher night-time temperatures. Leaving open, airy sides avoids a constantly damp enclosed space. Locations beside a wall, under eaves and in an open bed provide different conditions. Record these differences instead of using the shared label “garden” for all plants. [4-WWW] [1-WWW] [Koski 2019] [4-WWW] [1-WWW] [Koski 2019]

Greenhouse and indoor space

Under transparent cover, sunshine can quickly raise daytime temperature while the night-time minimum remains low. Measure conditions beside the collection as well as near the door. A sensor in direct sun may indicate its own heating rather than representative air temperature. Adjust ventilation to the weather and plant requirements. [Fleischer and Schütz 1978] [1-WWW]

Indoors, check the difference between air temperature and cooling beside the windowpane. Above a radiator, the stem and container may lose water quickly even though there is little light at the window. Warmth combined with watering may sustain growth with abnormal proportions. Reducing fertiliser does not replace improving light. A forest schlumbergera, in turn, should not be kept dry for months to follow the same care as an opuntia. [Fleischer and Schütz 1978] [1-WWW]

Seasonality and the hardiness of individual organs

Winter segments of Opuntia fragilis from Saskatchewan and its young growth responded very differently to freezing. In a controlled test, winter segments remained free of visible necrosis at −50°C, while new June segments died after ice was initiated at −3,5°C. At least five segments were used per temperature, the test was repeated three times, and assessment took place after four weeks. The implication for overwintering is to protect active growth and acclimate plants gradually, without treating the winter result as a universal species limit. [Ishikawa and Gusta 1996]

Roots may harden differently from stems. In clone 1279 of O. ficus-indica, after seven weeks at 20/10°C, young roots had an LT₅₀ of −6,5 ± 0,2°C and one-year-old segments −7,6 ± 0,2°C. Staining was assessed after a one-hour exposure of samples from 5–7 plants. The result supports measuring conditions in the root ball separately. Full comparisons and mechanisms are described in frost tolerance physiology. [Nobel and De la Barrera 2003]

Monitoring during dormancy

Examine stem bases, graft unions and stem depressions. A slow, even change in volume differs in meaning from a rapidly enlarging wet patch. Before watering a wrinkled plant, establish whether loss of firmness reflects use of reserves or impaired roots. Interpret a moist root ball and a wilting stem occurring together with particular care. [Fleischer and Schütz 1978] [1-WWW]

In grafted plants, rootstock needs remain part of the requirements of the whole system. A warmth-loving Selenicereus does not become frost-hardy when joined to a cold-tolerant scion. Observe the scion together with the union, rootstock tissues and roots. [Fleischer and Schütz 1978] [1-WWW]

Returning to growth

Increase light and water gradually in spring. A sunny afternoon does not mean sustained warming of the substrate or an end to night-time temperature drops. A plant moved from a darker room needs acclimation. The first watering should account for root condition, temperature and the prospect of root ball drying. [Fleischer and Schütz 1978] [1-WWW]

Complete the overwintering assessment after growth resumes. Record whether new roots and shoots have formed, whether damage is spreading and whether the plant flowers. A surviving fragment used to rebuild a specimen represents a different outcome from an undamaged plant. Such precision allows fair comparisons between seasons and provenances. [Fleischer and Schütz 1978] [1-WWW] [Fleischer and Schütz 1978] [1-WWW] [1-WWW]