01/01/2026
Happy New Year! Today's St. Louis weather is a predicted high of 40 degrees. Last Sunday our high temperature was 73. The next day's high was 27. Such extreme fluctuations stress many plants by expanding and contracting their cells, sometimes rupturing them, resulting in splitting bark or complete plant death. Warm spells can trick plants into breaking dormancy, prompting tender new growth that is then killed during the next freezing temperatures. Some plants are hardier than others, meaning they can withstand a wider range of temperatures.
All areas of the Earth have been assigned a hardiness zone, based on the minimum temperature range in which plants can survive. The most recent USDA Plant Hardiness Zone Map shows the City of St. Louis and the inner-ring suburbs are in zone 7a, with the minimum temperature from 0 to 5 Fahrenheit. But not all plants currently growing in our region can survive temperatures that low. We used to be categorized in zone 5 with higher winter temperatures, at which zone 5-bred crape myrtles and azaleas survived just fine.
Plants now outside our hardiness zone suffer dieback or even complete death when the temperatures dip dramatically. And some plants, like roses, have exposed crowns, which is the growth zone where the roots meet the above-ground stems, which make them especially susceptible to colder winter winds too. Other plants, normally winter-hardy, have recently been planted or transplanted, and their roots have not fully regrown and "connected" to the surrounding soil so they cannot fully support the plant material above-ground.
In all of these instances, the plants are helped by the extra protection of "volcano mulching". The photos show a newly planted forsythia and a mature rose with the crowns mulched. Extra mulch around the crowns insulate and help stabilize the plants' temperature, preventing the extreme temperature fluctuations from reaching the crown and the roots. If you have time and are not already one of our clients, it is not too late to help your plants thrive by doing the same.
In the spring, before the rainy season begins, we remove the winter mulch volcanos from the plants. That's because during the growing season, volcano mulching is not good for plants because it holds moisture against the stems and bark that prompts fungal growth and pest issues as the plant surface touching the mulch starts to rot.
