What zuzu wrote, plus, planting them against the west wall of your house likely increased the amount of heat they benefited from due to solar reflection and radiation. Even on the coldest days, if there is sun shining against the wall, there is some heat being reflected, absorbed and radiated out from it. That can easily raise the conditions in the close area a zone or two. The Brits were able to successfully grow cold tender plants against walls for generations. In the colder coastal areas here in California, planting against warm walls enables us to provide the required heat to make tomatoes, strawberries and citrus sweet, also due to the reflected, radiated heat.
