Climate Change: How does your garden grow?
by: Hilary Newell
From the time I moved to New England, people have told me, “If you don’t like the weather, wait five minutes.”
This maxim holds true more than ever in our shifting climate. Who ever thought, back when I was helping my mother plant our family vegetable garden each year, that our climate would be different by the time I reached this age. Different enough that the date of the first or last frost may have shifted by up to a week? Or changed enough that the iris would bloom a week earlier this year than it would have in 1975? The changes are subtle, but they are there, and we need to heed them and learn to adjust when necessary.
We gardeners have many wonderful attributes. Keen observers of the natural world, we notice when things are out of the ordinary. Like the fact
that the cherry tree at the end of my street that bloomed on or near the same date every year has been nearly finished blooming by that same date the last few years. Or how about the Kwanzan cherry trees, flowering almonds and plums that send out a second bloom in late fall or even early winter? It’s a bizarre thing to be driving down the road when everything has descended into dormancy, and suddenly: Pink.
We are undergoing a subtle and steady series of climate events that are going to impact our gardens and garden habits, and we would do well to be prepared to roll a little with the punches. But what’s the best way to figure out what is changing, and then how do we go about adjusting for that?
I’m the first to admit that my garden journaling has been pretty spotty. I have tons of photos and lists of varieties, but I haven’t been good about
keeping accurate records of dates when things bloom, or how well a new plant has done. We have anecdotal stories about the first and last frost dates, like the year it was 18 degrees in Tom Nevers on May 20, long after many folks had planted their tender annuals, basil and tomatoes. We remember the extremes, but not the ordinary.
Your garden journal will be an important tool to keep track of changes from year to year. It seems like it may only be a few years until Zone 8 shifts northward enough to impact our garden plans. Observing and journaling will provide better understanding of the fluctuating habitat.
I recently came across Habitat Network, an online forum created and hosted by the Cornell Lab of Ornithology. From its website: “Habitat Network allows users to map gardens, compile photos and document characteristics. If you are at all digitally inclined, this citizen science project can serve as your garden journal. Not only that, but the home gardeners, birders, educators and wildlife enthusiasts on the site are a fantastic group resource for finding out how to improve your garden or habitat. This will become more and more important as the climate changes. Weather anomalies and weird weather events are happening with greater frequency. These climatechange basics will change (have already begun to change) the fundamentals of gardening: what we should plant, where it should be planted, and when to plant it.”
Gardening has always been a steady touchstone for my husband and me. There is serenity and satisfaction when everything works out the way the vision leads. But the best-laid plans are just that, and wild and wonderful things can happen when we let go of our expectations. I suspect that is exactly what we all will have to do when planning and executing our gardens going forward.
A shifting climate may mean that we can push the envelope when it comes to choosing perennials. We may be able to choose some plants that wouldn’t have survived the winters previously, and certain perennials may not thrive under new conditions. Plants are complex and each variety has specific requirements for heat, moisture and light levels. Small changes in nature can cause big problems for some plants, though it is not all as predictable as one might think.
A study of over 300 species in Washington state found just the opposite of what was expected, with more than 60 percent of the species studied migrating to lower elevations as the temperature rose. On further study researchers realized the decrease in moisture (less snow and therefore less water available in summer) drove the plants toward the warmer temperatures at lower elevations because there was more water available there.
Other studies have shown that native plants of the southern United States are creeping northward, and traditional bloom dates have been skewed. Like the cherry tree above, the famous cherry trees in Washington, D.C. have been blooming earlier these last several years. Growers in the south report that rhododendrons are losing favor because they no longer thrive in the areas where they did decades ago. This is a good news/bad news scenario, though. On one hand, it means that plants that didn’t survive the winter in previous years will have a better chance of living through the winter. It’s fun to experiment, right? Subtropical plants in Pennsylvania? Cool. Palm trees in Knoxville? Whoa.
A perennial goes dormant over the winter, continuing to live underground until the air temperature and light reach the necessary levels to promote the growth of the crown. Tender perennials, also known as half-hardy perennials, may become full perennials for us. For our Zone 7 gardens, tender perennials are true perennials in Zone 8 or above.
There are a lot of Salvias that fit into this category. Salvia uliginosa is one of my all-time favorites, and on Nantucket, we currently need to replant it every year. But as our zone shifts toward 8, we will be able to leave them in the ground to come back each year. Azure-blue flowers with a white throat appear in late July and last until frost. Its alternate name,
bog rosemary, indicates that it likes swampy soil, but it does just fine in average garden soil, too. It spreads by underground runners, and in my garden, only about one plant lives through the winter, thus, continual replanting.
A warming climate means a slightly higher minimum winter temperature, and that means S. uliginosa will probably become a true perennial, finally gaining its full size of six feet. Similar is Salvia guarnitica Black and Blue. This South American native grows to about 18 inches as an annual here, but if it lives over the winter as a perennial it may well reach what the breeders indicate, up to four feet. Deep blue blooms may be more abundant with the stronger root system that a perennial provides.
Another favorite, Salvia Indigo Spires needs protection most years, but a warming climate will allow it to survive more frequently. As annuals, these never get the chance to reach their full potential. If they die back and have to be replanted, they are starting from scratch each year. If the roots survive and the plants re-sprout, they are getting a head start and will be fuller and grow with more vigor.
On a recent trip, I saw Dietes bicolor (yellow African iris) for the first time, and had to learn more about it. This fullsun plant is grown from a seed or division and is hardy in Zone 8, with evergreen, reed-like foliage. Flat, brightyellow flowers with deep orange/ red/brown centers decorate twoto fourfoot clumps of green. Like other iris, the flowers only last one day, but they are quickly replaced and continue to bloom for weeks. In Zone 7, these would need to be planted fresh each year, but they are currently listed as perennial in Zone 8 and south. Camellias are found in some protected gardens on Nantucket now and it is likely that camellia species and hybrids will be planted more. Hardy jasmine (J. officinale) also grows here, and breeders are working toward several new cultivars.
I’m pretty excited about some of the culinary herbs I’ll be able to grow in Zone 8 as these are likely to be perennials in the coming years. Herbs that are tender in Zone 7, like rosemary, French or Spanish lavender, pineapple sage, lemon verbena or bay laurel, are hardy in a zone that is just one step warmer. I plant two or three pineapple sages every year and enjoy the verylate-season bloom that attracts hummingbirds to our garden. In the last eight or so years, only one has ever survived the winter, and when it grew the following year, it was immense, it bloomed earlier, and it was so floriferous: a living illustration of the benefit of being a perennial, and not an annual.
Do you ever cook with bay leaves? There are two kinds of people who cook: those who love bay leaves, and those who don’t see any good use for them. We have one of each in our household, so we have kept them as houseplants from time to time. They can tolerate temperatures down to 20 degrees, so as our zone shifts upward from 7 (with a minimum temperature of 010, toward zone 8 with minimum temperatures of 10-15, bay will have a better chance of surviving outside in a protected spot.
About the only insect that bothers bay is scale. Fortunately, they are very visible, so you can probably keep your plant clean by inspecting it regularly. Scale on bay is easy to pick off when there are only a few, but if they get out of control, they are very difficult to treat. There is a lot of research out there about how insects respond to varying temperatures and light levels, but each year’s population of insects will be different because there is no such thing as a “normal” year. This is an area where we will have to be extremely observant, scouting for insects and treating for diseases as soon as they are discovered.
The most important thing you can do to keep pests at bay is to grow healthy plants. If you are purchasing plants, examine them carefully before you hand over your money. Don’t just look at the top of the plant but examine the roots as well. They should be firm and white, and evenly spaced around the pot. Clean your garden in the fall. I don’t mean it has to be spotless, but diseased foliage should be removed. Black spot on roses, daylily leaf streak and most fungal diseases can be minimized by consistent removal, particularly at the end of the season.
Applying the correct fertilizer at the correct rates and at the correct time will become increasingly important. Over-fertilization can cause plants to become more prone to environmental stresses, like too much or too little water, or temperatures that are too high or too low. I can’t emphasize enough the importance of testing your soil. The University of Massachusetts is the goto resource for this. For $15, the average homeowner can get a report to help figure this out.
Paying attention to the day-to-day in your garden will become more valuable as our climate changes at an apparently increasing rate. Committing to a journal, either online or by hand, is a wonderful approach to becoming more connected with your growing gardens. Documenting all the changes will help you understand the larger picture and allow you to modify your growing decisions each year.
The thought of an evolving growing season is pretty exciting in that it can give us the opportunity to grow more of our own food. Nantucket may experience an earlier last frost and a later first frost, and that could extend the greensgrowing season, or even allow some later crops of peas or beans. Warmer temperatures earlier could spell hastened ripening of tomatoes, or ornamental plants coming into flower earlier.
There are, however, far more serious implications to climate change than the effects on our gardens. Life in all its forms will be affected. The Colorado potato beetle has spread northward through Europe and now thrives where very cold winters had previously held it in check. Acute
oak decline is a disease that is now taking a toll on oak trees in the United Kingdom, where it had never been seen before the early part of this century. In South America, a coffee fungus is spreading, and other major crops like grapes and lavender are also threatened around the world. Indeed, food production is threatened as worldwide precipitation patterns change. Some areas are facing diminished rainfall while others deal with more intense and frequent flooding.
Gardening is a risky business, but gardeners are eternal optimists, always looking forward, always trying new things and always learning. I think the majority of Nantucket gardeners here are growing for pleasure, not out of necessity. And while we will certainly face challenges as the climate shifts, it will be exciting to learn which plants will be hardier and possibly perform better in areas where the climate is changing. ///
Hilary Newell is the marketing director at Bartlett’s Ocean View Farm and a regular contributor to Nantucket Today.