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Climate change: Hardy plants that are ready for it all

As I look back on last summer, both here in Vermont and all down the eastern seaboard, I recall it as incredibly dry and also very hot — not an easy time for our gardens.
And a quick check of the NOAA website for Burlington reinforced my impressions. The overall rainfall in the summer of 2016 was 50 percent below the long term average. A total of 15 inches of rain fell between May and October, compared with the long-term average of 22 inches, and every month was drier than the long-term norm.
Also, during those same six months, the average daily maximum temperatures were all several degrees higher than their long-term counterparts.
By contrast, just five years earlier, in 2011 we experienced excessively high rainfall. That year unprecedented flooding ruined spring planting — Vermont was even declared a federal disaster area. And everybody remembers, just three months later, the devastation caused by Tropical Storm Irene.
In an era of climate change, wide swings in the weather patterns are becoming the “new normal” — some years are unduly dry while others very wet. And at the same time we are also experiencing more extreme individual weather events — from high winds, to flooding and record snowfalls.
Gardening with climate change
Last fall I had a wonderful opportunity to spend a couple of hours, along with my colleagues at American Meadows in Shelburne, talking with gardening guru, David Salman, a recognized expert on gardening in an era of climate change.
Salman comes from New Mexico where he has been following changing weather patterns and their impact on plants. As he explained, the last five years the entire Southwest has been in the grips of an excessive drought. But, by contrast, the 1980s decade in New Mexico was one of wettest on record.
Since this pattern is also beginning to sound familiar to gardeners back east, I was particularly eager to see what advice Salman could pass along to help us prepare our gardens for the next drought that — despite this year’s chilly wet spring — will surely return in a year or two.
Here are his suggestions:
Conserve water
First, ensure the soil in your beds is flat, rather than mounded — especially at the edges. This helps the water penetrate the soil, rather than running onto the surrounding hardscape or lawn.
And, if possible, orient your beds with the long sides facing approximately east and west, as long south-facing beds tend to get parched in the mid-day sun.
Now look for places where water naturally collects, such as below the roof or near a solid driveway. Instead of letting this water run off into the storm sewer, create a ‘rain-garden’. This is essentially a gently sloped sunken bed that holds, and then gradually absorbs the excess water and irrigates the surrounding plants. A quick search on the Internet will give you plenty of ideas for plants that thrive in this environment.
And lastly, try watering your established plants less frequently — once a week or even once a fortnight should be plenty for most mature plants. But when you do water, always give each plant a thorough soaking (the equivalent of a 1/2 inch of rainfall). This will encourage your plants to develop deeper roots and thus need less water in the long run.
Enrich the soil
For hundreds of years gardeners everywhere have known the value of enriching their soil with compost. This magic ingredient creates a water-retentive soil with valuable micronutrients.
Mycorrhizae — which are specialized fungi that live in an intimate symbiotic relationship with the roots of most plants — are the second critical component of healthy soil. The secrets of mycorrhizal fungi and their unique contribution to the plant health is a fascinating topic that is still being actively researched.
Some types of mycorrhizal fungi surround the roots while others actually penetrate the cells of the host plant. But either way, the plant supplies the fungi with all their food — in the form of carbohydrates — and in return the fungi help the host plant absorb both water and nutrients from the soil while also protecting it from various pathogens.
Thus, in addition to our annual ritual of adding compost to our gardens, it behooves us to boost the mycorrhizal content in the soil. One approach is to brew a “tea” from the fallen leaves of the forest, and add it to the soil. Alternatively you can purchase packaged mycorrhizal additives. Either way these unique fungi enhance the ability of our plants to survive prolonged dry spells.
Check your microclimates
Even in a dry summer, there may be areas of your property that are wetter than the rest, so use these to your advantage.
For instance, since water runs downhill, low lying areas remain wet longer after it rains, making them suitable for many drought-tolerant plants that can endure periods intermittent dryness. The pin oak and swamp white oak are both considered drought-tolerant.
However, in very dry places, such as on a south or west facing slope, which will get baked in the afternoon sun, choose plants (like the bur oak) which are classified as xeric.
Winter advice
We are all aware that winters today are warmer than in the past, meaning the soil does not freeze as deeply. This makes it feasible to experiment with interesting perennials that may be rated as less hardy.
However, despite the trend towards higher average winter temperatures, once in a while frigid Arctic air escapes from the polar regions, resulting in short bursts of intensely cold air. While these short cold spells will not lower the ground temperatures significantly, they may damage less-hardy woody plants above the ground. So be more conservative when experimenting with less hardy woody plants.
And lastly, when the drought extends into the winter, plants actually succumb to drought rather than cold. So be sure to thoroughly irrigate any vulnerable plants — such as those you moved the previous fall — both before they enter dormancy in the late fall and again if the temperature rises above 50 F during the winter, when the roots can absorb it best.
Perennials to ponder
As we anticipate the prospect of more dry summers in our future, I suggest we begin to populate our gardens now with drought-tolerant plants, which will also thrive in the intervening wet years. (No I am not suggesting we all run out and buy cacti!) Here is David’s list of perennials for you to ponder:
Anise hyssop; Allium ‘Millenium’; Butterfly Weed (Asclepias tuberosa); Poppy Mallow (Callirhoe involucrata); Tick-seed (Coreopsis ‘Zagreb’); Dianthus ‘Firewitch’; Seed grown varieties of Echinacea; Sea Holly; Gaillardia; Dead-nettles (Lamium and Lamiastrum galeobdonblon ‘Herman’s Pride’); Rough Blazing star (Liatris aspera); Heirloom honeysuckle (Lonicera reticulata Kintzley’s Ghost); Wild Bergamot (Monarda fistulosa); All varieties of Catmint; Evening primrose (Oenothera macrocarpa); Ornamental oreganos; Ornamental grasses (except Muhlenbergia and Molina); Russian Sage; Black eyed Susans; Meadow Sage (Salvia ‘Blue Hill’, ‘May Night’ and ‘Caradonna’); Soapwort (Saponaria ocymoides); Both tall and groundcover types of Sedum; Goldenrod cultivars (Solidago); Yarrow.
Judith Irven and Dick Conrad live in Goshen where together they nurture a large garden. Judith is a Vermont Certified Horticulturist and teaches Sustainable Home Landscaping for the Vermont Master Gardener programs. You can subscribe to her blog about her Vermont gardening life at northcountryreflections.com. Dick is a landscape and garden photographer; you can see more of his photographs at northcountryimpressions.

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