Determining sun quality*


Can you tell us how to determine sun quality in the garden? There are many reasons I’d like to know, such as when the best time is to avoid the sun’s heat, when to water, how to select and place plants. It seems that only astronomers really know(and good gardeners). Could you also explain the terms on the plant packages, since “full sun” might have a connection to time, but does it equal the same amount of heat in spring as in the hottest time of summer?


Determining the sun quality in one’s garden is really not difficult. One certainly does not need to be an astronomer or even a gardener to understand that the earth’s relationship to the sun is constantly changing–that is why we experience four seasons during the year–spring, summer, fall and winter.  Because we live in the Northern Hemisphere, days gradually get longer between the Winter Solstice (ca. December 21st) and the Summer Solstice (ca. June 21st) and get shorter from the Summer Solstice until the Winter Solstice.  Gardeners are generally concerned about the sunlight during the growing season between April and October when the temperatures are warmer and the days longer.

One simply needs to observe where the sun is in relation to one’s garden in order to plan a garden and select plants . Where does the sun shine throughout the day? Not only is the position of the sun different each day during the growing season, it also changes throughout the day (the sun ‘rises’ in the East and ‘sets’ in the West).  If your garden faces South, it will generally receive much more sunlight than if the garden faces North; if facing East, it will have morning sun; if West, afternoon sun. Are there trees, shrubs, buildings creating shade during certain parts of the day or does the area have full sun exposure? No two gardens have the same light pattern and conditions.  

There are other factors that also need to be considered when gardening: not only do plants require varying amounts of sunlight for photosynthesis, they also need sufficient water, air, and nutrients/minerals from the soil to grow successfully. Another factor to consider is the temperature of the air and the soil–plants cannot grow when the air and ground are cold/freezing.

Plant packages or labels give some information as to the amount of light the plant needs during the growing season.  ‘Full sun’ generally means that the plant needs 6 or more hours of direct sun each day; it doesn’t need to be continuous–a plant could get 4 hours in the morning, shade during the mid-day when the sun is the hottest, and 3-4 hours more direct sun during the afternoon. ‘Partial sun’ means between 4 and 6 hours of sun per day; ‘partial shade’ may indicate between 2 and 4 hours; and ‘shade’ means at least 2 hours each day–most plants cannot exist without some sunlight. However, these terms are just guidelines. Nevertheless, one would know that a plant that requires shade would not do well if it was planted in full sun. Once you can determine what growing conditions you have, you can make appropriate plant choices.

To answer your question about ‘the best time to avoid the sun’s heat’, think about when you might want to avoid the sun–probably between noon and 3 p.m. on a very sunny and hot day. And because there are more hours of sunlight during the late spring and early summer, the temperatures are generally warmer than in the early spring.

When would be the best time to water a garden? Just as each plant has different sunlight requirements, each plant has different water needs. All plants need water; some need more than others. Some plants may wilt and die if they don’t have adequate water for the growing conditions. If it is hot and sunny, of course plants will need to be watered more frequently so that the soil doesn’t dry out. If it doesn’t rain occasionally, one will need to water the plants. The best time to water is in the early morning before the sun warms things up; if one waters during the hottest part of the day, the water will evaporate more quickly and the soil will dry out. And it’s important to know that when watering one’s plants, it’s much better to water enough so that the water sinks slowly and deeply into the ground than it is to water a little bit every day.

Once you understand what light requirements various plants need, then you can determine where the best place to plant them might be by observing the various sun patterns in your garden. But plants need more than light to grow successfully. You can learn more at:

Good luck with your garden.