After 33 years writing a gardening column for the Post-Dispatch, Chip Tynan is retiring from the Missouri Botanical Garden. We are rerunning some favorite columns for a few weeks, but the garden will resume the column soon. Please continue to send questions to the address below.
Q • I received an Italian Stone Pine as a living Christmas tree gift. I’ve been keeping it indoors, but I wonder if it can be planted outside?
A • The Italian Stone Pine (Pinus pinea) is not hardy in the St. Louis area and should not be confused with the Swiss Stone Pine (Pinus cembra), which will survive in our climate. Italian stone pines are native to northern Mediterranean regions in Europe. In this country, they are principally grown in California and areas of the western states that are not subject to freezing weather. Though they will not survive our winters if planted outdoors, neither can we consider Italian stone pines to be houseplants. If kept indoors in average warm conditions, they will eventually lose their vigor and decline.
Provide your plant with cool night temperatures in the 40s and a bright sunny window. A cool greenhouse or a sunporch would be ideal. For the remainder of the winter, allow the soil to dry somewhat between waterings. Place your plant outside for summer, with some protection from the hottest afternoon sun. Keep the soil evenly moist and fertilize about once a month until fall. Bring it back indoors in fall when night temperatures drop into the lower 40s.