Sweden : a place of choice to acclimatize tropical plants from June to September

Imported tropical plants can be given a bath with hormones or sugar after arrival then have to acclimatize in humid environments provided by plastic tents or tunnels, or foggers in commercial greenhouses. 
Following bath, humidity in the first days must be close to saturation and progressively decrease.

Most tropical plants acclimatize more easily at 18 - 20 Celsius rather than 35 C, and humidity, measured in gm of water vapor per cubic metre of air is better provided at 20 C rather than 35 C in temperate climates.

Too hot and too dry, they are twice disadvantaged.

Humidity in Stockholm, Sweden 

Temperatures in Stockholm, Sweden

From June to September in Sweden the average temperature suffices for the plants and the humidity is high ( not much lower than during the winter months ) so a gap in relative humidity at the start of a 2 weeks acclimatization ( the difference between the actual one and 80 % ) can be filled easily with plastic sheet or foggers.

The situation in Spain is just the opposite : the relative humidity in July falls sharply to 40 % while the heat is over 25 C and can even reach 32 C.
In Madrid on 3 July 2015 the humidity was only 19 % for 38 Celsius.

Las Vegas in the state of Nevada, USA, is even worse than Spain for the relative humidity and temperature relationship when tropical plants are concerned : the humidity goes down to an average 13 % in June !

Humidity in Las Vegas

Temperatures in Las Vegas

     If in Sweden at 18 C we enclose tropical plants in a plastic tent that makes one cubic metre of air around them, at a humidity of 60% the tent needs to hold over 9 gm of water vapour. Increasing to 80 % for a rooting or acclimatization period would require just over 12 gm : only 3 gm more in the tent.
In a situation like in Spain,  at 32 C and a humidity of only 40 %, 1 cubic metre holds 14 gm. The tent will have to hold 27 gm if the humidity has to increase to the higher level of 80%.  The difference is 13 gm, only a fogging system would fast provide enough water vapour to allow the plants to smoothly brace themselves for the dryer environment a few weeks ahead when we open the tent.

In Geneva the relative humidity is high and even more steady than in Sweden.

Humidity in Geneva, Switzerland

Temperature and humidity in Roma ( Italy ) : from March to July the average temperature rises sharply but the humidity is very consistent throughout the year.

Temperature in Roma

Humidity in Roma

The chart below shows the relative humidity in Bangkok, Thailand : it is high and steady over the months of the year, more or less as it is in Geneva ( Switzerland ) in Sweden or in Roma.


Humidity in Bangkok, Thailand

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