All living things, without exception, need food, water and a place to live.
Animals cannot make their own food, so they must eat plants or other animals. Because of that, animals evolved with the ability to move. That meant animals needed muscles, nerves, a central nervous system and brain to control it all.
Plants never evolved those structures because they are able to get everything they need to live in one place; if not, they die.
Why Plants Need Light
Plants make their own food. They evolved roots to access water and minerals from the soil. They also evolved trunks, branches and leaves to access sunlight. Plants have chloroplasts in their cells that make a green chemical called chlorophyl that combines carbon dioxide and water to produce glucose, as well as releasing oxygen back to the air. Glucose it a simple sugar that plants use both as a source of fuel and a basic building block for more complex organic molecules. Hence, plants need sunlight to live.
Are There Exceptions?
Some plants do not look green. Usually, they look red or tawny brown. These plants have chloroplasts and chlorophyl, however, they also have other pigments that are more visually pronounced. The chlorophyl is present and doing its job, our eyes just do not see the green or it looks very faint because other color pigments are visually dominant to our eyes. Those plants too need sunlight.
There is a small group of plants that are parasites. They do not have chloroplasts and chlorophyl because their roots graft onto the roots of other plants. These parasites live off the food produced by their host plant. So, while they do not directly require sunlight, they indirectly need it because they consume nutrients produced in plants that do require sunlight.
All plants need sunlight. Not only that, but because animals must eat plants or other plant eating animals; animals also require sunlight because we consume plants that require sunlight.
All plants use oxygen to perform photosynthesis. Photosynthesis uses sunlight as the energy source to combine water and carbon dioxide into simple sugars and oxygen. Those sugar molecules become both the basic building blocks of the plant and its source of food to fuel its other functions.
Xylem is a the plant tissue that conducts water and nutrients upward from the roots where they are stored to the other plant tissues where they are used.
The plant starves to death. Photosynthesis is the process that converts water and carbon dioxide into sugars that the plant uses both as building blocks and as a stored energy source.
Plant Hardiness zone map provided by USDA.
Deciding what plants will grow on your land takes some thought. While we all know that you cannot grow bananas in Ashland, figuring out what to plant where can be a challenge.
One of the first issues here in Wisconsin is the weather. Summers can be miserably hot while the cold … well, I don’t have to tell you how cold it gets. Still, where you live within the state makes a difference. Plants that grow well for you in Sturgeon Bay may die in the backyard of your brother-in-law who lives in Chippewa Falls.
The difference (aside from your brother-in-law’s black thumb) because the climate between the two properties is their climate zones. Both cities lie along the same latitude but their climate zones are very different.
The USDA plant hardiness zone map provides a convenient tool for determining the plant climate zone for your property. Nurseries and seed producers across the nation use this system to determine how they will guarantee hardiness for the plant stock and seed they sell.
Landowners should consider whether the place they want to plant has a microclimate that could alter their planting decision. Areas sheltered by buildings or south facing slopes might have warmer microclimates than the hardiness map. On the other hand, steep north facing slopes, especially those in dense woodlands, have microclimates cooler and wetter than the surrounding landscape.
Considerations other than hardiness
USDA hardiness zones should never be the sole criteria for selecting plants. Remember to look for plants that thrive with your soils and sunlight conditions. Those factors, just as much as cold tolerance, will determine whether your choices are happy or fail.
Our plants page contains other online tools as well as plant related resources and links to authoritative plant information.