Premature awakening, disrupted flowering, summer wilting, winter freezing: in my own modest way, devoid of bias and propaganda, I can only confirm a prevailing trend supported by rather indisputable data and observations: the notorious global warming. Typically, I refrain from delving into “trendy” topics. However, in the practical spirit of this compendium, I find myself pondering: “What lies ahead for gardens? What solutions can we implement?”
For someone like me, residing and working in the Mediterranean region, which is already characterized by arid summers, an effective solution involves creating dry gardens, gravel gardens, or similar landscaping approaches that conserve water. Another key strategy is the extensive use of native plants, which are naturally equipped to withstand certain “extreme” climatic conditions, particularly in the warmer months.
Nonetheless, as intriguing and efficient as these methods are, we can't possibly convert the entire world into dry gardens.
But let's proceed systematically.
Studies indicate that in temperate climates the seasons will not only be affected by higher average temperatures, but also their duration will be disrupted. These alterations will result in longer summers at the expense of increasingly shorter and warmer winters1. And it is precisely the changes in winters that raise the most questions. While plants in temperate zones are better adapted to cope with climate fluctuations compared to those in the equatorial belt2, I wonder how short and mild winters might affect their metabolism and physiology.
How will winter dormancy be influenced? Warm autumns may delay it, rendering plants vulnerable to early frosts3. Unlike early springs, which result in an anticipated awakening, warm autumns also seem to disrupt the timing of spring vegetative growth, causing unexpected delays4. Brief, mild winters can lead to plant-pollinator mismatches5, contribute to the persistence of pests and diseases6, and, in some instances, even transform non-native species commonly found in our gardens into troublesome invasive plants7.
Furthermore, we shouldn't forget that the global warming equation includes a host of local vulnerabilities stemming from extreme events and sudden climate variations, even during winter8. For instance, evidence indicates that stratospheric overheating leads to the Arctic polar vortex “fragmentation”, resulting in cold air incursions into North America and Eurasia during winter9. This phenomenon can cause extensive damage to plants unable to withstand extreme cold.
In regions with normally stable snow cover during colder months however, the action of thawing and freezing due to fluctuating temperatures in mild winters can lead to even severe damage to the root systems of those plants that normally benefit from the insulating power of snow10.
Late frosts can also have a great impact on new growing vegetation, especially in the case of early vegetative growth.
In conclusion, plant selection for gardens is far from trivial. The idea that higher average temperatures may allow the unintended cultivation of plants from warmer climates, such as the subtropical belt, can result in unpleasant surprises, particularly in winter. In recent years, I've lost specimens of plants like Lantana camara (common lantana), Plumbago auriculata (Cape plumbago), Polygala myrtifolia (myrtle-leaf milkwort), and Salvia leucantha (Mexican bush sage), just to name few of them, precisely due to frosty incursions into the Mediterranean region.
On the flip side, during scorching summers marked by intense heatwaves, plants native to temperate zones can succumb to rapid decay, not to mention the ubiquitous action of diseases and pests, which benefit from extended high temperatures.
So, what solutions? Perhaps loop can be closed precisely with the cultivation of plants native to the Mediterranean climate (in a broad sense, as this type of climate can be found in different areas of the planet, each with its own flora): many of them possess the remarkable ability to endure dry summers and harsh winters, which is no small feat. Think about Centranthus ruber (red valerian) Helichrysum italicum (curry plant), Lavandula angustifolia (common lavender), Myrtus communis (common myrtle), just to name the first four that came to mind.
Unfortunately, my confidence in this approach was shaken just this summer, as it witnessed the death of several Mediterranean species I cultivate. I'm still trying to piece things together, but it seems excessive humidity accompanying the heatwaves played a significant role. Moreover, the interplay between high temperatures and planting mediums with high water retention appears detrimental, causing these plants to wither and develop root rot.
The solution within the solution? The intricate puzzle is growing more complex. Perhaps the most effective approach will involve a meticulous evaluation of each single plant's growth capabilities, taking into account the specific ecological and climatic conditions of the garden in which it will reside. This is a practice already in place, but it's crucial to recognize that probably there are no more fixed canons to rely on.
Now, shall we wait for the white raven to appear?
Let's settle for the robin.
Jiamin Wang, Yuping Guan, Lixin Wu, Xiaodan Guan, Wenju Cai, Jianping Huang, Wenjie Dong, Banglin Zhang. Changing Lengths of the Four Seasons by Global Warming. Feb 2021. e2020GL091753.
Kristine Y. Crous Plant responses to climate warming: physiological adjustments and implications for plant functioning in a future, warmer world. Am J Bot. 2019 Aug;106(8):1049-1051. doi: 10.1002/ajb2.1329. Epub 2019 Jul 17. PMID: 31429920; PMCID: PMC6851979.
Danielle A. Way, Tree phenology responses to warming: spring forward, fall back?, Tree Physiology, Volume 31, Issue 5, May 2011, Pages 469–471, https://doi.org/10.1093/treephys/tpr044
Ilka Beil, Jürgen Kreyling, Claudia Meyer, Nele Lemcke, Andrey V. Malyshev. Late to bed, late to rise - Warmer autumn temperatures delay spring phenology by delaying dormancy. Aug 2021. https://doi.org/10.1111/gcb.15858.
Maxence Gérard, Maryse Vanderplanck, Thomas Wood, Denis Michez; Global warming and plant–pollinator mismatches. Emerg Top Life Sci 2 July 2020; 4 (1): 77–86. doi: https://doi.org/10.1042/ETLS20190139
Sandra Skendžić, Monika Zovko, Ivana Pajač Živković, Vinko Lešić, and Darija Lemić. 2021. The Impact of Climate Change on Agricultural Insect Pests Insects 12, no. 5: 440. https://doi.org/10.3390/insects12050440
Emily Haeuser, Wayne Dawson, Mark van Kleunen. Introduced garden plants are strong competitors of native and alien residents under simulated climate change. Nov 2018. https://doi.org/10.1111/1365-2745.13101
Evan Kodra, Karsten Steinhaeuser, Auroop R. Ganguly. Persisting cold extremes under 21st-century warming scenarios. Apr 2011. https://doi.org/10.1029/2011GL047103
Mark P. Baldwin, Blanca Ayarzagüena, Thomas Birner, Neal Butchart, Amy H. Butler, Andrew J. Charlton-Perez, Daniela I. V. Domeisen, Chaim I. Garfinkel, Hella Garny, Edwin P. Gerber, Michaela I. Hegglin, Ulrike Langematz, Nicholas M. Pedatella. Sudden Stratospheric Warmings. Nov 2020. e2020RG000708.
Frederick Curtis Lubbe, Jitka Klimešová, Hugh A. L. Henry Winter belowground: Changing winters and the perennating organs of herbaceous plants. June 2021. https://doi.org/10.1111/1365-2435.13858