How to garden in the ‘new normal’ that climate change is bringing – PennLive

Our changing and more erratic climate can threaten plants with surprise frosts, left, or "flash droughts," right.
Veteran gardeners used to have an edge over rookies because their years of weather experience told them when it was frost-safe to plant the tomatoes in spring and which shrubs are just winter-hardy enough to grow here or not.
Now? Not so much.
It seems our weather lately isn’t looking much like our weather past.
The latest set of weather “normals” from the National Oceanic and Atmospheric Administration backs up the observation that we’re in new gardening territory.
NOAA updates its weather norms every 10 years. Data is measured over 30-year periods at nearly 15,000 U.S. weather stations. The latest update shows that most of the country is significantly warmer and wetter.
Harrisburg has been getting a taste of both with a summer of 2020 that featured 32 days of 90 degrees or higher and its hottest month ever (July 2020), followed by a summer of 2021 that gave us nearly 12 inches of rain more than the norm and our third wettest September ever.
According to NOAA’s data, Harrisburg’s average annual temperature is now 1 degree warmer than just a decade ago, and our average annual precipitation is now nearly 3½ inches more.
That trajectory is expected to continue with one study from the University of Maryland and the North Carolina State University projecting that Harrisburg’s climate by 2080 will be similar to that of Jonesboro, Ark. That means almost 8 degrees hotter with January’s lows averaging only around the freezing mark.
Pam Knox, a University of Georgia agricultural climatologist, summed it up nicely in the Garden Professors blog: “We are not living in the climate that our parents or grandparents grew up in.”
A bit warmer and wetter might not sound like that big of a deal, but one problem is how we’re getting to these “new normals.”
Extreme weather events such as heavy storms can create soggy soil that kills plants.
Our weather events have become more severe, erratic, and unpredictable with ever-heavier downpours bracketing “flash droughts” and temperatures see-sawing from abnormal highs to abnormal lows – sometimes in a day’s span.
Plants aren’t good about dealing with these sudden changes.
And it’s becoming harder than ever for gardeners to decipher whether the new normal dictates planting tomatoes earlier or trying camellias if rogue weather events can upend both efforts in a single night.
If what really matters is the weather we’re about to get instead of what happened before, what’s a gardener to do?
Here are 10 thoughts on navigating the “new normal” in the garden…
These impatiens survived a light, late frost by being covered overnight.George Weigel
Our springs have been warming earlier, moving up our traditional “last-frost dates” on when it’s safe to plant summer flowers and warm-weather vegetables (tomatoes, peppers, beans, etc.)
Last year, for example, Harrisburg got its last frost April 23.
According to the most recent frost data from the National Weather Service, the median last spring freeze date now for Adams, Cumberland, Dauphin, Franklin, Lancaster, Lebanon, and York counties is April 11. That means in half the years, nighttime freezes are done by that date in those counties.
That doesn’t guarantee, though, that a single frosty night won’t come along to kill the petunias after we thought it was safe to plant them, as happened when a May 10 record low popped up in 2020 after a sustained, warm April.
A good compromise is to be ready to take advantage and plant early but to watch that 10-day overnight-low forecast before pulling the trigger… and be ready to cover the tender stuff in case the forecasts are wrong.
Our all-time latest spring freeze for Harrisburg is May 12. In outlying areas and north of Harrisburg, it’s close to Memorial Day.
Fall’s first killing frost also has been happening later, meaning we’re expanding our growing season on both ends.
The median date for fall’s first freeze is now Oct. 21 for most of south-central Pennsylvania but Nov. 1 for Adams, Lancaster, and York counties, according to NWS data. Harrisburg beat both of those last year.
The upshot is don’t be too quick to yank the season’s vegetables and flowers. If they’re still looking good and/or producing, let them go until frost finally shows up.
The longer back end of the growing season also means we’re better able to replant vegetable gardens in summer for fall harvests of such crops as cabbage, broccoli, kale, lettuce, beets, carrots, and even beans.
Could camellias be a new addition to Harrisburg-area gardens?
What used to be considered “borderline-hardy” plants are becoming better and better bets – species such as cherry laurel, crape myrtle, nandina, osmanthus, aucuba, fig, and vitex.
Warmer winters are even propelling us toward “new borderliners” that we might be able to get away with – such “southern” plants as camellia, Chinese fringe flower, red holly, alstroemeria, Caroline jessamine, edgeworthia, photinia, and even gardenias and some palms.
Again, consider that you might be fine for years, only to have one rogue night kill your gambles.
But if you’re willing to take the risk and/or mess around with winter covers and your yard’s warmer microclimates, experiment away.
Many plants begin to suffer when temperatures rise above 86 degrees. Since we’re seeing more and more of that (34 above-90-degree days last summer), it makes sense to gravitate toward plants that are adapted to heat.
One strategy is to pick perennial and annual flowers that do well in regions such as Texas, Arizona, and southern states, i.e. agastache, catmint, black-eyed susans, daylilies, penstemon, salvia, and gaura for the perennial garden, and ageratum, begonias, marigolds, sunflowers, verbena, vinca, and zinnias for the annual beds.
A second strategy is to look on seed packets and plant labels for varieties that mention heat tolerance and that list Heat Hardiness Zone ratings (the higher the number, the better).
On the flip side, plants that are native to cooler climates are likely to go downhill, including many spruce and fir species, hemlock, yew, sugar maple, heather, lupines, delphiniums, lady’s mantle, and primrose.
While a heat-killed lobelia or pansy is cheap and easy to replace, not so with trees. Those are bigger, long-term investments, not to mention expensive to cut down if next decade’s hotter climate kills what you plant today.
Chester County’s Longwood Gardens and the Chicago Botanic Garden have studied how different tree species are likely to fare in the future warmer climate and have identified these as probable strugglers: American beech; black cherry; gray birch; sugar maple; American and Greenspire lindens; Black Hills, Serbian, and Norway spruces; ironwood (also known as American hop-hornbeam); katsura, and Sargent cherry.
If you’re choosing trees with an eye on future heat, Chicago Botanic Garden lists these as better bets: ginkgo, Freeman maple, blackgum, bald cypress, American hornbeam, American yellowwood, serviceberry, Chinese juniper, redbud, Eastern red cedar, Persian ironwood, sweetbay magnolia, Winter King hawthorn, and red and white oaks.
Planting more trees in itself is a good climate-change-fighting tool because trees cool the ground underneath and are champions at capturing and storing carbon.
“Storms appear to be moving slower, and that is likely to lead to more rain from the storms over a specific area and more likelihood of rapid storm development,” Knox says.
Local dumpings led to flooding and root-rotted plants in 2018 and 2019, then 2021 brought us four summer storms of more than three inches each to put us nearly a foot of rain above what we usually get in July, August, and September.
“Water management of your gardens will become increasingly important,” Knox adds, citing such steps as planting bare areas to slow erosion, adding rain gardens to capture excess rain, and adding swales, French drains, and dry stream beds to cope with runoff.
The flip side is that periods between the aforementioned dumpings are getting hotter and drier, meaning our plants also are at increased risk of drought injury and death.
A mulch layer helps hold in soil moisture, while gardeners will have to be ready with the hose when these so-called “flash droughts” hit.
Installing a drip-irrigation system might make more sense than ever, too, to automate watering in the vegetable garden and/or annual flower beds.
Summer heat and long, dry spells are taking toll on our traditional cool-season lawns.
Hotter summers won’t be kind to our traditional cool-season turfgrasses (primarily Kentucky bluegrass, perennial ryegrass, and fine fescue), which already are increasingly browning and even dying in our new normal.
We may need to start switching to heat-tougher turf-type tall fescue lawns or to warm-season grasses that are more common just to our south, such as zoysia and buffalo grass.
Better yet, think about shrinking lawns and replacing some of it with more trees, shrubs, perennials, and groundcovers that reduce mowing, absorb rainwater better, sequester climate-warming carbon from the air, boost biodiversity, and help dwindling pollinator populations.
You’re not imagining it if you think weeds have been getting worse in recent years.
Not only are many weeds growing better in the warmer, higher-carbon-dioxide air, but we’re seeing new weeds that used to be too cold-wimpy to survive this far north.
Whether you pull them or spray them, the key is staying on top of the weed population and eliminating them when they’re small and haven’t yet gone to seed.
Weed preventers, mulch, and planting bare areas with plants you like (before weeds have a chance to colonize) are other tools in the arsenal.
Hotter weather and increased disease pressure are fueling the demise of cool-preferring species as this Colorado blue spruce.
As with weeds, our warmer winters are making it easier on species that used to die out over winter – in addition to more weather-unrelated invaders like spotted lanternflies and emerald ash borers. The longer growing seasons also are allowing some existing pests to produce more generations per year.
Warmer air means more humidity, and that leads to wet leaves and increased leaf disease (not to mention less pleasant summer gardening conditions for gardeners).
Scout plants regularly to sort out which bug and disease issues are tolerable, temporary, and cosmetic vs. those that threaten to kill plants. Then treat (or not) accordingly.
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