I started to see somewhat of a pattern working many of these things. The stories were slightly different, the plants were usually fairly close, but there was still a pattern.
Let me tell you one of them.
There was a gentleman that came to me with a Citrus question. It was a Meyer Lemon that he had, (my wife and mother just started chuckling....inside joke). He has had it for 4 or 5 years. When he first got it, there were tons of Lemons on it. The following year, it only had half of what it did the previous year. The next year was even worst. He wanted to know what was wrong. It was not even producing as many flowers.I started with my usual questions:
Is it in the ground or container?
"Ground"
How much water has it been getting?
"I water about every other to every third day."
Have you been feeding it?
"Yes, I feed it about every 6-8 weeks with Citrus-Tone."
How much sun is it getting?
"Full Sun"
I was getting frustrated. Usually a situation like this is easy to figure out. I started going for the off the wall stuff like insect pressure and dog watering it. Everything seemed fine.
I went back to what I was SURE was the problem.
I asked, You say it is getting full sun, if you had to put a number on how many hours it was getting, what would you say?
Then, like a voice from the heavens, the answer came in one small word....."FOUR"
BINGO!!
His idea of full sun was four measly hours. A live oak nearby had continued to grow and started to shade the Meyer Lemon more and more each year. I told him what he needed to do and he walked away satisfied.
This is the pattern I was describing, I have numerous stories, very similar to the one above. There is just a misunderstanding as to what exactly is considered "Full Sun".
Conventional thinking is 6+ hours of unfiltered sun is considered full. I tend to lean a little longer than that, I go for 7-8. Four to six hours per day is considered partial sun. Many companies use partial shade. These two terms are often used interchangeably to mean the 4- 6 hours of sun each day, preferably in the morning and early afternoon. However, if a plant is listed as partial sun, greater emphasis is put on it needing the minimal sun requirements. Less than four hours is considered shade. Anything less than two is deep shade. This does not mean that it needs no sun at all, there aren't many plants, except mushrooms, that can survive in the dark.
Sunlight is a necessity for plants to perform photosynthesis which is how they make food. Photosynthesis means ''putting together with light.' They use light energy to change the materials - carbon dioxide and water into food substances (sugars).If a plant does not receive enough sunlight, it will not produce enough sugars and will not grow as much as it would otherwise. A fruiting plant needs a great deal of energy to produce that fruit, that is why you hardly ever see a fruit plant grown in shade.
All plants have a threshold of how much sunlight is too much and how much is too little. Too much sunlight can also harm plants. Try planting a Hosta in Full Sun! Plants usually come labeled with their sun exposure requirements. Measuring that sun exposure is not an exact science. There will always be variables such as cloudy days and places where it gets to be 100 degrees in the shade. There are some plants that are listed as shade tolerant, but will grow in full sun, IF they have access to adequate moisture.
The intensity of sunlight varies depending on the time of day. A plant that gets sun all morning, but is shaded in the afternoon has a much different growing environment than one that does not get the morning sun, but is exposed to sun all afternoon.
There are many other variables to sunlight. A good gardener should know their yard and the side of the house that the sun comes up on. I have tried to explain many times to a gardener that a certain plant will do better if they plant it on the East side of their house. The immediate response is usually, "I don't know which way that is."
Simple answer, the side of the house the sun comes up on. Once you have that figured out, you can get the other directions. If you are facing the rising sun, North will be to your left, South to your right and West is on your back.
I usually tell people here in my Zone 8 that Citrus should be planted on the South or West side of the house. That way they have more heat directed to them.Citrus trees will do just fine in the morning, East sun, but they are usually a little more apt to get hurt in the Winter.
Now, just to muddy it up a little more. In the Winter time, as the sun settles down onto the southern horizon more, your intensity will tend to decrease here too. That 8 hours of sun you were getting a month ago will not be as strong. If you notice your plant starting to reach for sunlight, this could be the reason. Try to find an even brighter location until the sun starts coming back to the North in the Spring.
Latitude and elevation play a role too. Gardens in the South receive more intense sun than those in the North. And gardens at higher elevations are brighter than landscapes at sea level.
Sometimes trying to help people with their plant problems is like pulling teeth. You have to pull and yank to get all the pertinent information from them. Then if they are misinformed about a certain thing, it can make it even harder. I hope this brief description of what the sun does, how much is needed, and where you get the most was helpful.
If you ever have a plant that is just not doing well, evaluate the environment you have it in, water, food, sunlight...the plant will tell you what it wants, that tag that came with it.....not so much. I can give you a list of plants that the tag says one thing, being sunlight amount or that it will grow in a certain Zone, and it is wrong.
Happy Growing!
Darren