How to Adapt Your Garden to a Changing Climate
Last summer, I stuck up a pleasant conversation with Will Hsu, a prominent ginseng farmer in the state of Wisconsin. It was March, and the temperature at lunchtime had risen to more than 70 degrees.
“Isn’t it a gorgeous day?” I asked.
“No, it’s really bad,” he said.
Why wasn’t he pleased to be outside on a warm day after a long winter? Wisconsin’s history of cold winters and cool summers make it an ideal climate for growing ginseng, Hsu told WKOW. He was concerned for his crops, and with good reason.
Temperatures throughout the U.S. have been on the rise, most notably in the past 30 years, according the U.S. Environmental Protection Agency website. In fact, the 10 hottest years on record have happened since 1998.
But perhaps the most perplexing elements to farmers—and gardeners—are not the slowly climbing temperatures across the board, but sudden shifts in temperature (from warmth to frost and back again) and unpredictable patterns of precipitation, including heavy rains and drought, which can damage certain species of plants.
Noticeable effects in the changing climate
So how much does the temperature have to shift before a plant is affected?
Well, that depends on the plant, according to Brian Sullivan, The New York Botanical Garden’s Vice President for Gardens, Landscape and Outdoor Collections.
“All gardeners know the frustration of dealing with the vagaries of weather,” Sullivan said. “We get excited to put out our vegetable starts on the first spring-like day, only to find them nipped back by a hard frost a few weeks later. Or newly planted perennials in May could suffer from an unseasonal heat wave before they have successfully settled into the garden.”
Shifting temperature ranges are especially challenging for plants that flower once in early spring, like blueberry, according to Sullivan. If blueberry plants are flowering when the temperature drops unexpectedly, the flowers don’t perish in the cold, but the pollinators nevertheless are inhibited from pollinating and fruit set is lost for that season, he explained.
Know your zone
If you’re looking to start a garden and aren’t sure how to select plants, Laura Musacchio, associate professor in the department of landscape architecture at the University of Minnesota, recommends that find out where you fall on the United States Department of Agriculture Hardiness Zone map. Once you identify your zone, you can cross-reference that with a list of plants that thrive in your region.
“According to the U.S.D.A., the plant hardiness zones are determined by average annual extreme minimum temperature over a period of 30 years,” Musacchio said. “It’s that cold that can really affect a plant over time. The different zones on the map cross state lines. The mapping is pretty general, but it’s a great place to start.”
In addition to these broad zones, it’s also important to know your “microclimate,” according to Musacchio. The microclimate surrounding your home can be influenced by the amount of trees and shade, propensity for wind and even the ratio of evergreen to deciduous trees.
Coping with changes to your garden
Once you understand your garden’s climate, you’ll have a good idea of the plants that will thrive there, but, in the words of the Ancient philosopher Heraclitus, “the only constant is change.”
You may have a good thing going in your lawn right now, but the bottom line is this: keep an eye on your current conditions and be prepared to adapt. “The best option in dealing with any growing conditions is to work with the conditions you have,” Sullivan said.
Here are some tips for planting when your garden is too…
“Gardens with severe topography will always have a low point and this is where water will naturally collect,” said Sullivan. “This is a great opportunity to plant water-loving plants.”
Adding or improving drainage can help with resolving wet conditions. A French drain can be easily added to move the water from a wet area.
If you’re looking for plants suitable to drier conditions, you’ve got lots of options. Sullivan recommends plants lavender for full sun and Epimedium for dry shade.
“Perennial bulbs like daffodils do well in dry gardens, since they need dry conditions when the plant is dormant to ensure the underground bulbs don’t rot,” Sullivan said. “Plants with deep root systems, like grasses, are especially suited for dry gardens, as their deep root systems are able to seek out water at deeper depths.”
A garden may be dry for lack of rainfall or as a result of competition from tree roots, according to Sullivan. He also notes that gardeners can also add compost to the soil to increase water storage capacity and a layer of mulch to help retain moisture.
If you like flowers, we’ve got good news for you: a sunny garden is an ideal spot for blooms. Many flowering plants demand full sun, and will flower less and be weaker if planted in anything less than full sun, according to Sullivan.
“Plants needing more sun will often stretch in the direction of the sun, indicating that they are planted in too much shade,” Sullivan said.
A sunny garden provides lots of options. “The list of sun-loving plants is long, indeed. Roses, dahlias, and salvias are some of the favorites,” said Sullivan. “Herbs and vegetables, too, appreciate as much sun as they can get.”
With a woodland garden, you have the opportunity to create a unique, lush experience.
“A dappled area can be a beautiful place to garden, especially if the shade is from deciduous trees,” Sullivan said. “This is a great opportunity to plant spring ephemerals like bloodroot and trillium, which thrive in the spring sunlight of a deciduous canopy.”
Once shaded as the canopy leafs out in summer, Sullivan points out that the garden is perfectly suited to growing ferns, sedges, and other dry woodland plants.
5. Frosts, thaws and frosts again
Gardeners in cold climates know the frustration of losing new plants to a late frost, and that frustration is bound to grow as the weather becomes more unpredictable.
“Ideally, once a hard frost has occurred, the soils stay frozen until spring when the thaw begins,” Sullivan said. “In the case of an extended winter thaw, early spring plants will respond and may start to grow or flower and all plant parts exposed will be vulnerable to a freeze.”
The best way to protect against this, Sullivan says, is to avoid early spring-flowering plants. Still you can minimize the damage to the roots of plants if you anticipate a few cycles of freezes and thaws.
“Plants should be planted 6 weeks from the typical freeze date,” Sullivan says. “This allows roots to develop to anchor the plant against heaving out of the soil. A thick layer of mulch can be added after the ground has frozen to minimize fluctuations in soil temperature.”
Also, the less water in the soil, the better it will weather changes in temperature. “Improving the drainage in the garden will reduce the water in the soil that causes the expansion and contractions of the soils,” Sullivan says.
Neil Gilbert, floriculturist foreman at the Garfield Park Conservatory in Chicago, notes that some plants, especially conifers, benefit from water in the soil before a frost.
"While water in the ground is prone to frost heaves and thaws, watering plants well before deep freezes, particularly new planted perennials, woody plants, conifers or plants in raised beds," said Gilbert. "Conifers desiccate, meaning they dry out in winter winds, and available ground water helps protect their health during mini-thaws. I would advise new gardeners to continue to water their plants into the fall."
Consider plants that help conserve water
In certain climates, you might be either required by water restrictions or motivated by water bills to reduce the amount of water that you use to maintain your garden. And if you’ve followed the recommendations above, you should be in good shape, according to Musacchio.
“Water conservation is trying to match the right plant to the site,” Musacchio observed.
“Cacti and succulents are the classic water conservation plants,” Sullivan says. “Eastern prickly pear cactus and sedum thrive in rock outcroppings and shallow soil and use very little water.”
Sullivan also notes that many perennials that thrive in dry conditions and, once established, don’t require any supplemental water. “In many cases native plants are perfect candidates to conserve water,” Sullivan said. “Yarrow, agasatache and catmint are all capable of thriving in low water conditions.”
Raised beds and why they matter
You may have seen them in your local community garden or in a neighbor’s yard—raised beds are gaining popularity for several reasons. A raised bed is either a bed that has been mounded above ground level or one above ground constructed from a wooden frame, according to Sullivan.
“One immediate benefit to a raised bed is improved drainage,” Sullivan said. “If the soil is wet and heavy, planting in mounded raised beds allows the plant roots to be in dryer soil, while still having access to the wetter soil below. A constructed raised bed has a number of benefits in addition to improved drainage, one of the most important is that it allows more control of soil quality.”
In fact, Musacchio recommends that individuals get their soil tested— for several reasons.
“Get your soil tested,” Musacchio said. “It will help you figure out the quality of the soil that you have, and to match the type of plants that can grow successfully there. If the soil quality is not good, a raised bed is an ideal solution, but check with your local university extension service or garden center to get specific advice for your particular situation.”
Raised beds are also ideal as a temporary garden—if you’re not sure you’re ready to commit to gardening for the long haul—and for those gardening in small spaces, according to Sullivan.