With polar ice caps melting and 2006 on record as the second warmest year in recorded history, it’s obvious to all but the most self-deluded denialists that global warming is real and is accelerating.
This will make a big difference in the kind of plants, trees and other crops you can grow. When you read the articles on this website that discuss growing vegetables and fruit, you’ll note that some types of fruit trees need cool temperatures if they are to properly set and produce fruit.
You will also find advice about what time of year is safe to start growing vegetables outdoors. In many parts of the country, if you plant too early, a frost may come along and kill your crops.
Most plants and trees are limited in where they can grow, and two of the main limiting factors are maximum and minimum temperatures, and when those temperatures occur.
For a century, agricultural experts have created “hardiness” zone maps that tell growers where and when they can grow crops and when they can plant them and harvest them. Local and regional climate realities govern those maps and what kinds of plants and trees will grow there.
People have relied on the same maps for years, but global warming is changing the equation. As overall temperatures rise, winters will become shorter and warmer so gardeners will be able to plant many varieties of vegetable crops earlier.
Growing seasons will be extended and potential for frost damage will recede. If some of the more dire predictions about climate change come true, it will be so warm that people living in many parts of the United States will be able to grow vegetables outdoors year round.
This sounds wonderful, until you examine the details. Rises in temperatures caused by global warming is likely to wipe out or severely damage millions of acres of forests, orchards, gardens and other landscapes that have adapted to the traditional climate that is being rapidly decimated by global warming.
This damage is already happening in places like British Columbia, Canada, where millions of acres of forests are dying because winter temperatures are no longer cold enough to kill pine beetles that destroy trees.
People who rub their hands in glee thinking that warming will only change temperatures and can therefore be counted on to produce predictable and profitable agricultural effects are victims of a shallow understanding of the effect of temperature on the water cycle, soil health, and overall ecosystem stability.
Not only will warmer winter temperatures likely spell the end of apple orchards in the Northeastern United States, but they will also wreak havoc on water supplies, rivers, animal habitat and migration, and forest health.
Winter isn’t the only season likely to warm up. Summers will also get hotter- the likely effect being that cities will turn into heat traps, electricity grids will fail, and thousands of citizens will experience heat-related illness or even death.
Speaking agricultural and ecological terms, warmer summers will mean damage or death for animals and plants- due to drought, fire, loss of soil moisture, dried-up rivers, extreme UV exposure, and other effects of warming.
Warmer temperatures are also likely to result in larger blooms of insects at the same time that the heat kills hundreds of thousands of birds that eat insects.
Organizations such as The National Arbor Day Foundation have finally caught up with the facts of global warming and are issuing corrective information that alters the geographic mapping of zones that can support specific trees and plants.
Based on the latest comprehensive weather station data, The National Arbor Day Foundation just released a new website (arborday.org) Hardiness Zone Map which separates the country into ten different temperature zones to help people select the right trees to plant where they live.
The new map reflects that many areas have become warmer since 1990 when the last USDA hardiness zone map was published. Significant portions of many states have shifted at least one full hardiness zone. Much of Illinois, Indiana, and Ohio, for example, have shifted from Zone 5 to a warmer Zone 6. Some areas around the country have even warmed two full zones.
In response to requests for up-to-date information, the Arbor Day Foundation developed the new zones based on the most recent 15 years’ data available from the National Oceanic and Atmospheric Administration’s 5,000 National Climatic Data Center cooperative stations across the United States.
Hardiness zones are based on average annual low temperatures using 10 degree increments. For example, the average low temperature in zone 3 is -40 to -30 degrees Fahrenheit, while the average low temperature in zone 10 is +30 to +40 degrees Fahrenheit.
The new 2006 arborday.org Hardiness Zone Map is consistent with the consensus of climate scientists that global warming is underway. Tree planting is among the positive actions that people can take to reverse the trend. Tree planters across the nation can go to arborday.org, click on the Hardiness Zone link, and enter their zip code to determine their hardiness zone.
“The Arbor Day Foundation supports tree planting throughout America,” says Foundation President John Rosenow. “Providing the hardiness zone for individual zip codes at arborday.org is an important part of that goal, by giving tree planters the most up-to-date and useable data available.”
“Of course existing trees should continue to be cared for,” said Woody Nelson from the Arbor Day Foundation. “Certain species may be more vulnerable to stress with the current warmer climate, but they will continue to provide environmental and economic benefits as they grow. It’s just a good idea to consider more tree species diversity for the future.”
Trees counteract global warming in multiple ways. Atmospheric carbon dioxide is the leading contributor to global warming, and as trees grow they remove CO2 from the atmosphere, storing the carbon and releasing oxygen.
A single tree can remove more than a ton of CO2 over its lifetime. Also, shade provided by trees reduces summer air conditioning needs. The cooling effect of a healthy tree is equal to 10 room-size air-conditioners operating 20 hours a day.
Trees reduce the “heat-island” effect in urban areas, where summer temperatures are generally warmer than the surrounding countryside. According to the U.S. Forest Service, 50 million strategically placed shade trees could eliminate the need for seven 100-megawatt power plants.
Trees around homes and in cities slow cold winter winds, reducing the need for winter heating. This relief on fuel consumption for heating and cooling helps reduce CO2 emissions from burning fossil fuels.
Detailed information about which trees are best for planting throughout the country, the value of trees, and the latest warmer hardiness zones can be found at www.arborday.org.
Vegetable gardeners are also of course affected by global warming. So far, the vegetable seed and home gardening market has been slow to react to global warming. It has yet to revise the zone system contained on seed packets and on charts at retail gardening stores.
This system tells people what crops they can grow in specific geographic locations. It also tells people when to plant the crops, based on temperature statistics.
But because winters and warmer and shorter and the onset of spring is earlier in many locales, inaccuracies have crept into much of the long-standing advice about what crops will grow properly outdoors at various times of the year.
Most gardeners are familiar with the U.S. Department of Agriculture’s Plant Hardiness Zone Map. By using the map to find the zone in which you live, you can determine which plants will “winter over” in your garden and survive for many years. You can also determine when to plant crops.
That map was first published in 1960 and updated in 1990. Today nearly all American references books, nursery catalogs, and gardening magazines use USDA zones.
But as we all know, cold isn’t the only factor determining whether our plants will survive and thrive. Particularly during drought, we are all aware of the impact heat has on our plants. And the effects of global warming will bring a broad range of negatives that probably will offset any gains caused by warmer winters.
The effects of heat damage are more subtle than those of extreme cold, which will kill a plant instantly. Heat damage can first appear in many different parts of the plant: Flower buds may wither, leaves may droop or become more attractive to insects, chlorophyll may disappear so that leaves appear white or brown, or roots may cease growing.
Plant death from heat is slow and lingering. The plant may survive in a stunted or chlorotic state for several years. When desiccation reaches a high enough level, the enzymes that control growth are deactivated and the plant dies.
The American Horticultural Society (AHS) Plant Heat Zone Map can be used like the aforementioned Hardiness Map.
Start by finding your town or city on the map. The larger versions of the map have county outlines that may help you do this.
The 12 zones of the map indicate the average number of days each year that a given region experiences “heat days”-temperatures over 86 degrees (30 degrees Celsius). That is the point at which plants begin suffering physiological damage from heat. The zones range from Zone 1 (less than one heat day) to Zone 12 (more than 210 heat days).
Thousands of garden plants have now been coded for heat tolerance, with more to come in the near future. You will see the heat zone designations joining hardiness zone designations in garden centers, references books, and catalogs.
On each plant, there will be four numbers. For example, a tulip may be 3-8, 8-1. If you live in USDA Zone 7 and AHS Zone 7, you will know that you can leave tulips outdoors in your garden year-round. An ageratum may be 10-11, 12-1.
It can withstand summer heat throughout the United States, but will over winter only in our warmest zones. An English wallflower may be 5-8, 6-1. It is relatively cold hardy, but can’t tolerate extreme summer heat.
Gardeners categorize plants using such tags as “annual” or “perennial,” “temperate” or “tropical,” but these tags can obscure rather than illuminate our understanding of exactly how plants sense and use the growth-regulating stimuli sent by their environment.
Many of the plants that we consider annuals-such as the petunia, coleus, snapdragon, and vinca- are capable of living for years in a frost-free environment. The Heat Map will differ from the Hardiness Map in assigning codes to “annuals,” including vegetables and herbs, and ultimately field crops as well.
Plants vary in their ability to withstand heat, not only from species to species but even among individual plants of the same species! Unusual seasons-fewer or more hot days than normal-will invariably affect results in your garden.
And even more than with the hardiness zones, we expect gardeners to find that many plants will survive outside their designated heat zone. This is because so many other factors complicate a plant’s reaction to heat.
Most important, the AHS Plant Heat-Zone ratings assume that adequate water is supplied to the roots of the plant at all times. The accuracy of the zone coding can be substantially distorted by a lack of water, even for a brief period in the life of the plant.
Although some plants are naturally more drought tolerant than others, horticulture by definition means growing plants in a protected, artificial environment where stresses are different than in nature.
No plant can survive becoming completely desiccated. Heat damage is always linked to an insufficient amount of water being available to the plant. Herbaceous plants are 80 to 90 percent water, and woody plants are about 50 percent water. Plant tissues must contain enough water to keep their cells turgid and to sustain the plant’s processes of chemical and energy transport.
Watering directly at the roots of a plant-through drip irrigation for instance- conserves water that would be lost to evaporation or runoff during overhead watering. In addition, plants take in water more efficiently when it is applied to their roots rather than their leaves. Mulching will also help conserve water.
There are other factors that can cause stress to plants and skew the heat-zone rating. Some of them are more controllable than others.
Oxygen. Plant cells require oxygen for respiration. Either too much or too little water can cut off the oxygen supply to the roots and lead to a toxic situation. You can control the amount of oxygen your plant roots receive by making sure your plants have good aeration-adequate space between soil particles.
Light. Light affects plants in two ways. First, it is essential for photosynthesis-providing the energy to split water molecules, take up and fix carbon dioxide, and synthesize the building blocks for growth and development. Light also creates heat. Light from the entire spectrum can enter a living body, but only rays with shorter wavelengths can exit. The energy absorbed affects the temperature of the plant. Cloud cover, moisture in the air, and the ozone layer-factors we gardeners can’t control-affect light and temperature. But you can adjust light by choosing to situate your plant in dappled shade, for instance, if you are in its southernmost recommended heat zone.
Daylength. Daylength is a critical factor in regulating vegetative growth, flower initiation and development, and the induction of dormancy. The long days of summer add substantially to the potential for heat to have a profound effect on plant survival. In herbaceous perennials and many woody species, there is a strong interaction between temperature and daylength. This is not a controllable factor in most home gardening situations.
Air movement. While a gentle spring breeze can “cool” a plant through transpiration as it does us, fast-moving air on a hot day can have a negative effect, rapidly dehydrating it. Air movement in a garden is affected by natural features such as proximity to bodies of water and the presence of surrounding vegetation, as well as structures such as buildings and roads. You can reduce air circulation by erecting fences and planting hedges.
Surrounding structures. If the environment is wooded, transpiration from trees and shrubs will cool the air. On the other hand, structures of brick, stone, glass, concrete, plastic, or wood will emit heat and raise the air temperature. Gardeners wanting plants to produce early or survive in cold zones will often plant them on the south side of a brick wall. Obviously, this would not be a good place for a plant at the southern limit of its heat zone!
Soil pH. The ability of plant roots to take up water and nutrients depends on the relative alkalinity or acidity of the soil. Most plants prefer a soil close to neutral (pH 7), but there are many exceptions, such as members of the heath family, which prefer acidic soil. The successful cultivation of any plant requires that it be grown in a medium within a specific pH range. While it is possible to manipulate the pH of soil with amendments, it is easier to choose plants appropriate to your soil type.
Nutrients. Plants vary greatly in the ratio and form of elements they need for consistent, healthy growth. It is important to get quality nutrients and supplements from Advanced Nutrients so you can give your plants exactly what they need. If you are not sure what they need, contact our experts and they will advise you.
The AHS Heat Zone Map is a valuable tool, and can be purchased from AHS by calling (800) 777-7931 ext. 137, or by writing the organization at 7931 East Boulevard Drive – Alexandria, VA 22308 USA.
The long-term effects of global warming are only partially understood and must be carefully considered by anyone who is a serious gardener, farmer, landscaper, orchardist, or otherwise into growing plants and/or trees.
For example, if you have just moved into a home and are planning to include a productive garden and fruit trees in your landscape design, it is advisable to do thorough research about short and long-term climate changes in your area before you do your landscape plan.
If you have an existing orchard, garden, greenhouse operation or other important plant or tree-based business or hobby, you owe it to yourself to get accurate climate information so you can minimize damage to existing plants and trees and also maximize your area’s transition into a warmer and probably drier climate.
You will need to talk to soil scientists, other ag experts, climatologists and government officials to get a full picture on how global warming will affect your ability to grow plants and trees.
Several products from Advanced Nutrients can help you protect plants and trees from the likely effects of global warming. Perhaps the most important of these is Barricade, which strengthens plants and trees internally and externally so they can resist drought, high temperatures and other stressors.
Another important protective product is Scorpion Juice, which increases the vigilance and power of plant and tree immune systems so they can better resist drought, heat, disease, insects and other attacks.
Plants and trees suffering in stressful environments need living soil with healthy soil bacteria and fungi. These are provided by Voodoo Juice, Tarantula, and Piranha.
Sad thing is that global warming may well make large parts of the United States unfit for agriculture.
Something similar happened in 1930. It was called the Dust Bowl. The Dust Bowl was caused by climate changes, but it was also caused by land abuses created by industrial agriculture, and it led to the death of millions of acres of productive soil.
Tens of thousands of people were thrown out of work, and vast areas of the US dried up and blew away. The country’s food supply plummeted, and its economy was ruined.
Today, with the entire earth atmosphere under threat from human-caused pollution, those of us who love growing plants and trees have to wonder if humanity has learned the lesson and will do what it takes to reverse global warming, or if we are witnessing the last days of photosynthesis on our planet.