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Why are my lemons not turning yellow?

A contributing reader, (Marge Adams), recently asked a great question about citrus fruit ripeness. Like many, she would like to know why her lemons are not turning yellow.  Since this issue may become a common dilemma for more people due to climate change, I thought it would be useful to write a short article about it.  

Paraphrased reader question:

‘I have a healthy looking Meyer Lemon tree but the fruit is NOT turning yellow.  Any ideas as to why my lemons look like large limes and do not turn yellow?’

 

Color for ripeness:

Fruit color is usually a great indicator for ripeness.  Crops ranging from peaches to guava typically develop beautiful-rich appealing colors when they are ready to eat.  However, there are some fruits, such as citrus, that may not always change color as expected.

Half yellow lemons at bottom and flowers at top of picture

Half yellow lemons at bottom of the picture and flowers at top of picture

 

Warm weather green: 

As it turns out, many citrus require a temperature dip to stimulate the fruit to change color.  Therefore, when the weather is persistently warm, your lemons may not turn yellow as you would expect.

To complicate things, sometimes only part of the fruit changes color. This finding may be an indicator that it is on it way to ripeness… or that something else is going on.  If the partial color change is sharply demarcated, it might be a sign of sunburn. Sunburn is often (though not always) also associated with areas of browning on the fruit surface. Sunburn can result from sudden intense sun exposure to previously shaded areas after tree trimming or from spraying chemicals such as oils at the wrong time of day.  For more info about appropriately spraying your citrus trees check out my article titled, Citrus Leafminer: Diagnosis and Treatment.

This warm weather green citrus fruit phenomenon is actually a common in some parts of the world.  For example, in the tropics, it is expected that some citrus fruit varieties will never lose their green color the way they would in subtropical climates such as California.  Of course on the other hand, Limes are expected to be green when ripe even in subtropical areas.  For more info on growing limes check out my article titled Bearss Lime Tree Care

Even more surprisingly, sometimes citrus fruit will turn their expected yellow/orange color and then later turn back to green. This may happen if the weather becomes persistently warm again.  I know, that is crazy right?

 

Developing Kumquat fruit showing signs of sunburn

Developing Kumquat fruit showing signs of sunburn.

 

So now how do you determine ripeness?

When your citrus fruit do not turn their characteristic yellow or orange, you need to utilize other indicators for ripeness. I use 3 additional signs of citrus fruit ripeness when my citrus don’t change color on schedule.

Note: Citrus are not known to ripen off the tree like many other fruits.  Therefore, once picked, they are not going to get any sweeter.  This can be a bit confusing because many citrus that are picked green will also change to their expected bright yellow/orange color as they sit on the kitchen counter.

Meyer lemon fruit dropped before turning yellow

Meyer lemon fruit dropped before turning yellow

 

One of the best indicators: 

One of the best indicators of citrus ripeness for me is the firmness of the fruit. This is because citrus fruit typically soften a bit to the touch when they are ripe. Different types of citrus soften to different degrees, so the firmness indicator takes some experience for a particular variety of fruit.

Overall, if your citrus fruit are not turning yellow/green as expected, then it is time to, ahem… to start fondling them.  If the fruit is the softness of ripeness, (the way you remember from experience), pick one and try it out.

Squeeze your lemon

Squeeze a few of your overdue green lemons

 

Another indicator of ripeness: the drops: 

Another indicator of ripeness is that citrus fruit will drop off the tree on their own when ripe (or over ripe).  Now sure, sometimes fruit will drop off a plant on its own when if the plant is stressed or diseased.  Therefore, this indicator is not perfect.

Better still, to identify fruit that will fall off the branch with a gentle tug.  Sometimes just looking at the stalk (where the fruit attaches to the branch) will let you know its time. A stalk will sometimes look markedly angulated or start to pull away at the edges when a fruit is extra ready.

In addition, when you allow the fruit to ripen to the point of dropping on its own you run the very real risk of waiting too long.  Since citrus sweeten and lose their acidic tang over time, waiting to this point may also change the flavor profile.

None the less, if everything else looks good and healthy, when your tree starts to drop the fruit you should pay attention because you might be missing the boat… or your tree might be sick.

A half yellow Meyer Lemon. The stalk is bent and just looks like it wants to be plucked

A half yellow Meyer Lemon. The stalk is bent and pulling away. It just looks like it wants to be plucked.

 

The moving on indicator, flowering: 

Another useful indicator that I have noticed is that many citrus trees start to flower when the hanging fruit is ready or near ready to pick.

This indicator is not perfect either, but it is another one of those things to pay attention to.  If your citrus is flowering massively then it might be cycling through to the next round of fruit.

Ripe meyer lemon and flower buds.2

Ripe Meyer Lemon and flower buds.

 

Wonderful Meyer lemon flowers

Wonderful Meyer Lemon flowers

 

Overall strategy:

Overall, in these warm weather conditions, I tend to utilize all of these markers for ripeness.  It is also important to sample the fruit conservatively because once picked, your citrus fruit will stop ripening.

More Meyer Lemon info:

Prolific Meyer Lemon tree

For great info about how to grow Meyer lemons, check out my article titled Growing Meyer Lemons

You like lemonade? You will love Meyer Lemon Lemonade. Here’s a link to an article I wrote about how to make it yourself at home Meyer Lemonade Recipe

About Thomas Osborne, MD

Dr. Osborne is a Harvard trained Radiologist and Neuroradiologist who loves to share his insight about medicine and gardening.

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