Wintering your cactii
It is necessary in winter, unless you have the good luck to live in the extreme south of France, to bring your cactii and other succulent plants indoors. Their morphology is adapted to dry conditions and allows them to store a lot of liquid. The liquid stored can be up to 50 to 80% of the weight of the plant ! The strored liquid is essential for the survival of the plant in extreme weather conditions and renders it even more sensitive to frost.
Cleaning before wintering
From the first sign of autumn chill, stop watering and fertilizing the cactii immediately. Verify each pot to check that there are no parasites on the plants. Look closely around the collar and under the plant to check that there are no scale insects present. Signs of their presence are whitish traces in the form of small concentric circles ressembing cotton ! Take the time (and patience !) to remove them by hand one by one using a solution of alcohol and oil.
Check that there are no brown stains on your plants. If this is the case on plants with a cylindrical form, treat them with a product which fights against cryptogamic diseases and isolate them.
If blackish stains appear on the leaves of your agaves this means that they contain too much water. Cut the leaves affected, leaving just the "head" if necessary, treat them and keep them in a dry place.
Don't repot
It is best to wait until the soft spring weather to repot your cactii. Inspect the roots and the substratum to find out if the plants have been subject to an underground attack. Root lice are partial to certain kinds of cactii.
A very dry winter
If you wish your cactii to flower spectacularly in April, let them relax totally, unwatered in a cool place. A cold greenhouse is ideal, but an unheated or slightly heated bright room will do the job. Most cactii in the wild survive in sub-zero temperatures on condition that they weren't rained upon, so temperatures of 10°C or 12°C are quite suitable for them.
In parts of the south of France, it is possible to winter them outdoors providing that they are sheltered from rain and frost, and are kept in a sunny place. These will produce spectacular flowers!
Be careful with plants which are similar to cactii, like the Rhipsalis (mistletoe cactus) and the Epiphyllae, which come from tropical areas and which don't tolerate temperatueres below 6°C.
Minimal treatment
Once your plants are installed, leave them be. Don't water them and certainly don't fertilize them. They will thus pass winter peacefully and hassle-free and will marvel you with their wonderful flowers when the soft weather comes back around !