It's true... the inside of a cucumber on the vine measures as much as 20 degrees cooler than the outside air on a warm day.
A Gardener's Guide to Zone Maps Which climate zone do you garden in? Why does it matter?
What zone do you live in? This may seem like an odd question, but the answer is one of the most important guides to knowing which plants will thrive in your garden. A variety of maps, including some new ones, can help you find the information you need. Understanding climate zones is critical for selecting permanent landscape plants. If you want a shrub, perennial, or tree to survive and grow year after year, the plant must tolerate year-round conditions in your area: the lowest and highest temperatures, the amount and distribution of rainfall (or availability of irrigation), and soil conditions. In eastern North America, the most commonly used zone map is the United States Department of Agriculture (USDA) Hardiness Zone Map, devised in 1960 and revised in 1990. This article explains the origins and uses of climate zone maps, including those four.
Which Zone Map - Perhaps the safest course to ensure plant adaptability is to grow only plants native to your particular region. Native plants have proved they can survive in your climate. However, plants don't stay in their regions of origin any more than gardeners do. Plants native to China, Siberia, and Mexico thrive alongside each other in many American gardens. Furthermore, a California gardener may want to grow a plant that's native to the Great Plains. In such cases, gardeners need a way to compare their garden climates with the climate where the plant is known to grow well. Zone maps provide critical climate information.
Making Sense of Zone Maps - Zone maps are fairly recent innovations. German geographer Alexander von Humboldt created the first one in the early nineteenth century. Humboldt used lines, called isotherms, to delineate regions of equal temperatures. In 1927, horticulturist Alfred Rehder created a system of eight isothermic zones for most of the United States, with each zone separated by temperature differences of 5 degrees F. He was the first to relate average winter minimum temperatures to the hardiness of specific plants. In 1931, German geographer-meteorologist Vladimir Koppen published a zone map divided into regions that share similar native vegetation. By studying and classifying vegetation types, Koppen ensured that his map accounted for rainfall, humidity, elevation, soils, and the myriad other factors that affect plant growth. All of the climate zone maps in use today derive from these two prototypes.
Heat Zone Map - 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 will be able to determine what plants will "winter over" in your garden and survive for many years. That map was first published in 1960 and updated in 1990. Today nearly all American references books, nursery catalogs, and gardening magazines describe plants using USDA Zones.
But as we all know, cold isn't the only factor determining whether our plants will survive and thrive. Particularly during seasons of drought, we are all aware of the impact that heat has on our plants. And although there is still disagreement in the scientific community on this issue, many believe that our planet is becoming hotter because of changes in its atmosphere.
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.