Sunlight and Shelter Needs
of Trees and Shrubs
Every tree or shrub you may plant in your landscape has its own preferred growing environment and unique needs for sun, soil, and wind exposure.
Understanding Tree and Shrub Needs
Often, trees or shrubs will hang on to life despite great challenges. But they always do best when they receive ideal conditions and can thrive. What are those needs?
The coldest tolerable temperature is one limit on trees and shrubs survival in your yard’s landscape. Plants are adaptable, sometimes to a wide range of growing conditions. Their survival instinct is remarkable and noteworthy.
Some are tender tropicals that wither and die when the thermometer drops under 50°F (10°C). Others are well-adapted to extreme cold; many willows persist in arctic regions where winter temperatures fall to –40°F (–40°C).
Exposure to cold depends on the revolution of the earth around the sun, the tilt of its axis, and the distance of a site from the equator [See Earth’s Orbit, this page].
While many global and local conditions affect the climate, the lowest temperatures generally are felt in the highest latitudes, during seasonal winter. The extreme years, when winter temperatures drop to record lows, are key to whether each tree or shrub in your yard lives or dies.
The U.S. Department of Agriculture (U.S.D.A.) has mapped the averages of those extreme cold temperatures and created plant hardiness zones for the United States. GrownByYou adapted the same data and zones to other regions of the world for the convenience of all gardeners [See U.S.D.A. Plant Hardiness Around the World].
For best results and successful landscape plantings, always choose plants suited to your own plant hardiness zone.
Earth's Orbit
Sun and Shade
Like the right climate, all green plants, shrubs, and trees also need sunlight to fuel their conversion of nutrients and carbon dioxide into sugars within their cells—photosynthesis.
Depending on their leaf or needle structure and adaptation to climate, they may do best in full sun, full shade, or somewhere in between, filtered sun or partial shade.
Compare the well-recognized “shade plants,” ones with broad, flat leaves able to gather in every bit of sunlight that reaches them, to while cacti and succulents. These plants of the arid deserts have very small leaves, drop them when drought begins, or lack visible leaves altogether.
Choose plants for your landscape in the “sweet spot:” Ideal sunlight conditions they tolerate well.
Match full-sun species to areas of your yard with 8 or more hours per day of sunlight. Plant partial-shade trees and shrubs in spots with 4 or more hours of sunlight and full-shade plantings where they will get at least 2 hours daily.
Soil Acidity
Life and photosynthesis in trees and shrubs depends on chemistry. Soil temperature, moisture, and levels of acidity or alkalinity speed up and slow down these chemical reactions in your trees and shrubs.
Most trees and shrubs are adapted to soil conditions with an acid-alkaline balance—or pH—in the range of 4.5 (moderately acidinc) to 8.0 (very alkaline).
Plants that prefer alkaline soils will fail in acidic soils, as will those that are acid-tolerant but planted in alkaline soil.
Sometimes a tree or shrub will cry out for help before they die, developing a cultural illness called chlorosis, or yellowing of their foliage, from too alkaline conditions. They are signaling that they can’t take up sufficient iron, manganese, and zinc, minerals essential to their health.
Another common issue is salt exposure for plantings near streets or sidewalks that are salted during freezing weather. Again, leached salt makes the soil more alkaline than ideal for many species of trees and shrubs.
Correcting the pH of the soil solves both of these problems in a matter of days. Generally, treat soils with chelated iron or garden sulfur to make them more acidic, or with garden lime to increase alkalinity.
Wind Exposure
Because having sufficient water is the last important requirement for landscape plant health, drying winds are thieves robbing trees and shrubs of moisture. Strong wind exposure means uneven growth, stunting, or even death to your landscape plantings.
Where possible, provide broadleaved deciduous or evergreen trees and shrubs wind protection by choosing the least-exposed sites in your yard for them.
Conifers and other needle evergreens have less foliage to resist winds. They can tolerate exposed sites better.
Always stake trees planted in sites exposed to the wind to prevent breakage or other wind damage.