I have from different sellers 3 variegated Euphorbia lactea crests (including 'Grey Ghost' and 'Topaz') all grafted onto the same stock, which is another Euphorbia. None of the sellers know what the stock is and I want to know the name to determine the minimum temp the stock can tolerate without damage so I know when I need to bring the plants back indoors from outside. The stock is nearly perfectly rounded, dark green, with sporadic leaf nodules every couple inches apart up and down the stem. It is about the thickness of a broomstick. Anybody have any idea the name of the stock and/or any opinion about minimum temp the plant can tolerate outside ? Would much appreciate any feedback.