How to Garden in an Unfamiliar Climate

Maybe some of this sounds familiar: Spring makes an extra-early start, in a month that not so many years ago felt more like it was part of winter. Then, when the calendar says spring is barely over, summer arrives as a heat dome — and without the much-needed soaking rain.

Just as early April masqueraded as May, June impersonated August. And all bets were off.

To expect the unexpected may be the best advice for gardeners facing unfamiliar weather patterns driven by a changing climate. But how do we do that?

Things are shifting, and the gardener’s focus must shift along with them, especially when caring for woody plants, said Daniel Weitoish, the arboriculture supervisor at Cornell Botanic Gardens, in Ithaca, N.Y. Our updated job description is likely to require anticipation and triage, not simply scheduled maintenance.

“Rather than just looking at a calendar and saying, ‘It’s July 15, time to do X or Y,’” he said, we have to be “a caretaker, watching and reacting to what signs the plants are showing.”

Things are no longer happening in the order we’re used to, so we have to tune in for clues, and get to know the garden in this new world order.

“Being present, watching, knowing what to look for: It feels more intimate communicating with the plants and listening to their needs,” Mr. Weitoish said.

He knows, for example, that various dogwoods (Cornus) are indicator species — revealing stress early, before it shows up in other trees and shrubs.

“Many dogwood species are going to wilt, and their leaves are going to curl,” he said. “It’s the poster child for what you could look for in many of your other plants if you’re like, ‘Do I need to start triaging?’”

He added: “Flagging foliage that doesn’t rebound during a cool or wet period is even more concerning.”

In June, the stand of Katsura (Cercidiphyllum japonicum) trees at the Cornell gardens signaled with a hint of their own.

Typically, in the heat of late summer or early fall, as Katsura leaves start to break down, they emit the scent of cotton candy or burned brown sugar. “We detected that smell in June this year,” Mr. Weitoish said, recalling how a cool, wet spring had suddenly shifted to 90 degree weather. “They were stressed; they got hit hard with the temperature transition. Those trees that expect to have this long roll into summer just haven’t had that chance.”

Even the familiar Annabelle smooth hydrangea (Hydrangea arborescens Annabelle) showed its displeasure, and stressed-out red maples (Acer rubrum) started showing fall color during high summer.

What signals has your garden been giving you? Take note — and take notes, for future reference, because not every symptom will coincide with a current weather event.

That’s another part of the equation, Mr. Weitoish explained: Trees are on a different timescale. They have “a metabolic memory,” he said, as if they keep “a budget or ledger of their reserves.”

Because of that, he added, “looking at what weather and climate and pests and stressors were like over several years goes a long way” toward understanding what we are seeing now.

One example: If there is a very dry fall, trees may defoliate early. By the following spring, we may have forgotten that stressful autumn, but the plants haven’t. If more insults follow — an early warm spell causing the tree to leaf out, for example, followed by a late frost — the effect is cumulative.

“And then summer comes, but it’s not that hot of a summer, and we’re wondering why is everything suffering?” Mr. Weitoish said.

Mitigating stress when it’s happening can head off compounded effects later.

Watering Mindfully, Creating Shade

There are some important don’ts to remember when you’re dealing with stressed plants: Don’t prune them, and don’t fertilize, either.

If you see yellowing foliage, get it diagnosed with help from your county cooperative extension service. (Find yours here.) Don’t intervene without testing the soil. There has never been a more important time for gardeners to connect with expert hyperlocal resources.

Much of the tactical to-do advice seems obvious, but there is a new urgency — and less room for error.

It’s no surprise that a conscientious watering regimen is essential in gardens where erratic rain patterns and bouts of intense heat are becoming more commonplace. “We want rain to take care of watering, but if it hasn’t rained for a week or so, or if it’s been shallow drizzles, that’s when we start to take closer looks,” Mr. Weitoish said. “Dig a finger into the soil, and if the top three inches are dry, I’d start watering.”

You may have heard this before, but it bears repeating: Gardeners armed with a hose nozzle suited to car-washing may be giving plants a bath, not a proper drink. Water infrequently but deeply, drenching the soil rather than the plants. Bark on trees and shrubs that is constantly wet can lead to decay; repeated watering on foliage contributes to fungal diseases.

Soaker hoses are an excellent way to put water only where it is needed. And make sure to do your watering at night or in the morning, rather than in the heat of day.

Mulch is another essential tool, both to retain soil moisture and regulate soil temperature. The Cornell gardeners use mulch made from ramial wood chips (chipped small and medium-size branches) composted with fall leaves.

Better Plant Choices, Smarter Planting

Identify the areas in your garden that seem to have suffered the most in recent years. Some plants that used to handle full sun, for example, may not acclimate to a more intense version of it. Do you transplant them or modify the space?

At the botanic garden, a structure of slatted wood known as a lath house provides permanent shade for some plants, but there are simpler solutions.

Planting a coniferous tree on the southwest side of a garden can mitigate afternoon sun that’s harsh on perennials, understory trees and shrubs. “It’s probably not going to shade it this year,” Mr. Weitoish said. “But five years from now, you’ll have started to chip away at the problem.”

Until then, light-blocking shade cloth — woven polypropylene fabric available in various densities — could serve as a temporary rescue for small-scale plantings. Tarp-like versions sold hemmed and with grommets are easier to set up on supports than unfinished material in rolls.

Although many of a gardener’s management decisions are made in response to weather — specific events at a given moment — it’s time to make some longer-term choices in anticipation of where the bigger pattern of climate is headed.

When a new U.S.D.A. Plant Hardiness Zone Map was issued in November, gardeners in half of the country learned that their locations had officially shifted. Many saw their average annual extreme minimum winter temperature (the metric the zones are based on) designated a half zone, or 5 degrees, milder, confirming something they had probably already felt.

The Cornell Botanic Gardens, formerly Zone 5b, is now 6a, presumably widening its palette of winter-hardy plants. This year, for the first time, the staff planted crape myrtle (Lagerstroemia indica), a flowering tree long synonymous with Southern gardens. Mr. Weitoish is also enthusiastic about Southern magnolia (Magnolia grandiflora) and bigleaf magnolia (M. macrophylla).

Whatever the species, proper planting is critical to its success, particularly with all of the additional stressors. The goal: maximum resilience.

“Take the time to do what’s best for the roots,” he said. Remove trees or shrubs from their nursery pots and spread the roots out, positioning them so that the root flare — where the first structural roots meet the trunk — is at soil grade or slightly higher.

Once the plant is positioned and the hole backfilled and mulched, use water — not your foot — to settle it in. No stomping on the planting surface, he said. Let the watering wash the soil particles downward, displacing any air pockets.

More Pressures, and Hope

There is so much more to think about.

“Changes in disease patterns are really being seen,” Mr. Weitoish said, noting fungal pathogens like cytospora and rhizosphaera appearing in spruces. “It’s really hard to grow Picea pungens, the Colorado blue spruce, and several other spruce species.”

The increased humidity promotes fungal issues. Bouts of heat can interfere with pollination in various crops (think: tomatoes). Some pests are having a field day, able to extend their range into new regions and possibly produce more generations of offspring in the extended frost-free season.

At some point, winters will simply be too warm in many traditional areas for the venerable sugar maple, scientists predict.

The Cornell team members are tuned in to all of this, but nevertheless undeterred. Just as they are trying out new tree species, they have also embarked on other future-thinking projects, including the installation of a water-wise gravel garden.

Hard times have prompted updated guidelines for drought preparedness and the like, certainly. But the outcome of recent strategic planning sessions wasn’t all protocols and procedures.

There was another important mandate, as well. “One of our essential values,” Mr. Weitoish said, “is to be purveyors of hope.”

Margaret Roach is the creator of the website and podcast A Way to Garden, and a book of the same name.

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