Winter: Zones, Climate, Soil
Scientists and creationists agree on one thing—plants have been around longer than we have. During that time, they have adapted to an amazing variety of conditions: arctic tundra, blazing deserts, volcanic islands, and peat bogs.
My granddaughter Paige recently got her dream job (her term) in a local nursery. She loves plants and arranging flowers. I also worked in a nursery when I was about her age. Luckily, she doesn’t have to unload truckloads of steer manure in 100-degree heat. Ah, the sweet smell of progress!
The other day, Paige asked about some plants that she wants to grow in her bedroom window. Some were ferns, others were succulents and cacti. I had to warn her that succulents and cacti often grow in warm, sunny environments, and might not do well in her cool, shady basement apartment. As a budding plant lover, she is just discovering all the many variables that affect plant life.
In a prior almanac, we talked about the phases of a plant’s life: dormancy, germination, growth, bloom, and senescence. While most plants (or at least flowering plants) have these phases, the variations are nearly endless. The wide variety of plants is due to the wide variety of places they grow—you can’t treat them all the same and expect them to thrive!
All life as we know it needs water. Some plants live in deserts, where water is extremely scarce; others live completely immersed in water. Some water is fresh, some brackish, some salty, and some downright hostile, like the Great Salt Lake, the Dead Sea, or volcanic hot springs. Plantlife exists in all of these environments!
Plants have an astonishing variety of mechanisms to take in and store water. We are all familiar with trees that send down long taproots to access deep sources of water, but did you know California coastal redwoods actually take in most of their water through their leaves, from coastal fog? While their cousins, the giant sequoias, can grow in Utah (Will has one in his backyard), coastal redwoods could never live in Utah, which has no coastal fog.
In deserts like Utah, plants need to make the most of what little water they get. Cacti, for example, are designed to easily expand and contract as water becomes available—and they have spines and needles to keep animals, who are much more mobile, from using them as their main water source. Some plants have thick skins, strong flavors, or poisons to get animals to avoid them, while others develop flowers to get animals to help them.
Utah’s Great Salt Lake is what’s left of an inland sea, which evaporated until it became too salty for fish. Several kinds of algae live there, which feed brine shrimp, which support birds, a fish food industry, and are the “Sea-Monkeys” advertised in old comic books.
Oceans hold many kinds of plant life, from microscopic phytoplankton that feed whales, to rich kelp forests rising hundreds of feet from the ocean floor. Specialized plants live in brackish tidewaters and estuaries between the oceans and rivers, and still others fill freshwater rivers and lakes.
Sunlight and seasons
As a rule, plants need sunlight. Some plants get full sun all day, some part of the day, and some get only filtered or reflected light. Some plants stretch upward to create a forest canopy, gathering all the light they can, while others live on deeply shadowed forest floors, and survive on a lot less. There are a few plants that don’t even have chlorophyll (e.g. Ghost Pipe) but they get their nutrients from other plants, or from fungi, which in turn get their nutrients from green plants in decay, so yeah, it all comes from the sun one way or another.
The equator gets equal amounts of light and dark every day; it gets one season, or often two (wet and dry). But the tropical zone, which lies between the Northern Tropic, or Tropic of Cancer, and the Southern Tropic (Capricorn) are the lines at which the sun can be directly overhead, and they change a bit over time as the earth shifts its tilt relative to its orbit. Tropical plants are often adapted to a constant, fairly warm, and often dry climate, so they tend to be best adapted as house plants.
Farther north or south are the subtropics and the temperate zones, which have our typical four seasons, though they are reversed—July is summer in the north, but winter in the southern hemisphere (Australian and Brazilian schools have summer vacation in December and January). Plants here often need a winter season (or weeks of cold stratification) to germinate seeds. A greenhouse or cold frame can be used to extend the growing season, and take the edge off cold nights.
Cold-hardiness is also a factor in temperate zones. USDA hardiness zones are based on average lowest annual temperatures, which indicate how cold-hardy a plant has to be to survive outdoors. Sandy, Utah, where I live, is zone 6b (0 to -5 F), while coastal Puerto Rico is 12b (55-60 F), and Nome, Alaska is 3b (-30 to -35 F). I’m glad I don’t live in Nome, but we get some extreme weather too—Peter Sinks, about 13 miles west of Bear Lake, gets some of the coldest temperatures in the continental United States, with -69 F recorded in 1985.
Nome is 200 miles below the Arctic Circle. Above the Arctic Circle (or below the Antarctic), the sun never rises or sets during some part of the year. Days and nights that last longer than 24 hours are hard for plants (and people) to deal with, so the few that survive in the arctic/antarctic tundra have to be well adapted to that harsh environment.
Even equatorial plants can range from sea level to the (rapidly-disappearing) snows of Kilimanjaro. Many plants are adapted to life at a particular elevation range. Temperature, seasons, air pressure, dew point, and precipitation are all different at elevation, and flowers that bloom in March or April in the valleys may bloom in July or August in mountain pastures. High mountains have a “tree line” above which the trees disappear; as you move farther down towards the valley, the number and variety of trees and other plants will also change. The Edelweiss is the national flower of Switzerland and Austria because it’s native to the high Alps—you’d have a hard time trying to grow it as a houseplant!
Soils vary in many ways and have several components. These include decomposed rock, which may be igneous, metamorphic, or sedimentary in nature. The rock or mineral particles may be of different sizes: large, coarse sand; smaller particles, easily carried by water, called silt; and very fine particles that form clay when wet. In geology, loam is a roughly equal mixture of sand, silt, and clay. Soils usually also include varying amounts of organic materials, primarily from decomposing plants and leaves.
Water drainage is one aspect that varies greatly between different soils. Sandy soils absorb and drain water quickly, keeping little water between the particles. The usually dry stream in front of my house sometimes runs only partway down the hill, suddenly disappearing completely into the sandy river bottom. Clay soils absorb slowly and drain poorly, sometimes leading to runoff, erosion, and mudslides. Organic material varies but often absorbs very slowly when bone dry, absorbs much better when already slightly damp, and holds on to water much better than sand, releasing it slowly as plants need it.
Plants breathe through their roots as well as their leaves, and air is an often overlooked aspect of soil. Tightly packed clay, sometimes called hardpan, can be nearly as impenetrable to air as it is to water, and many roots have a hard time with it. For the same reason, soil that is full of water can prevent roots from getting the air they need—the roots can “hold their breath” for a while, but if they can’t breathe for too long, they drown. Plants that live underwater use their roots mostly as anchors, and draw oxygen from the water, like other underwater life.
Soil can also vary in its acidity or alkalinity, which is measured in pH. The pH scale goes from 0 to 14; water is neutral at 7.0; lower than 7 is acidic and higher than 7 is alkaline. Alkaline soils are caused by decomposing shale, limestone, and other sedimentary rocks. Acidic soils are created as organic matter decays. Alkaline soils are more common in the west, where mountains are newer and forests and prairies are younger. Alkaline conditions make minerals hard to dissolve—like that mineral crust that builds up on your faucet—so many plants (not all) do better in acidic conditions. Soil pH ranges from highly acidic peat bogs (pH 3.2-4) where Sphagnum moss thrives, to alkali deserts with a pH above 8.5.
A surprising number of plants don’t need soil, such as “air plants” (Tillandsia). Many orchids anchor to tree bark and do their own thing. Many water plants, like duckweed, just float through life, while others depend on a whole environment—soil, fungus, other plants, animals, and even coastal fog—and don’t do well if any of the needed elements are removed.
I hope you enjoy the diverse, beautiful, and often wondrous world of plants as much as I do!