In the garden: Why won’t my tree fruit?

No matter if you are a commercial grower or a backyard tropical fruit enthusiast, if you have a fruit tree, you want fruit. The number one question I receive — I am the commercial tropical fruit agent for all of South Florida — is: “Why won’t my tree fruit?”

A mango tree with no fruit is just a shade tree after all.

A number of factors combine to create a tree healthy enough to fruit. A healthy tree must have a strong root system, adequate light, proper pruning, proper nutrition, the right age, no mechanical damage, proper irrigation, and must have been planted properly.

When the “Why isn’t my tree fruiting?” question comes my way, I go into tropical fruit CSI mode and ask these questions:

▪ Is the tree getting full sun? Producing fruit takes a lot of energy, and trees create their energy by using the sun through photosynthesis. Without enough sunlight, a tree will not bloom. Without bloom, there is not fruit. If your tree is shaded by your house or a taller tree, it will have trouble producing fruit.

▪ How old is the tree? If the tree is older than three years, it should have at least bloomed by now, unless the tree was grown from seed. Most fruit trees are grafted, meaning they have an already mature portion of a known cultivar — for instance a ‘Haden’ mango, grafted onto a healthy seedling.

The graft accomplishes two things. One, you know the exact type of fruit you will get as this is basically a cloning process.

Two, the tree skips all the stages of maturity and is instantly sexually mature. A tree planted from seed has to be baby mango, toddler mango, texting mango, snapchat mango, high school mango, college mango, married mango, and then finally the tree is old enough to fruit. A tree can take up to 15 years to become mature A grafted tree is always recommended.

▪ Does the tree look healthy? If the tree is green and the leaves are all fully formed, it is most likely not dealing with any issues that would stop it from blooming and setting fruit.

If the tree has a trunk caliper of five inches or less, I will often ask the client to give it the “shake test,” where you actually go out and see if you can move the trunk. If the trunk moves along with its roots, that is a sign of a weak root system, which may have been caused by too much water or a girdled root system before the tree was planted. Trees with weak root systems often have difficulty obtaining nutrients.

If the trunk moves, but the roots do not, then the root system is most likely strong.

▪ When was the last time the tree was pruned? A fruit tree that was severely pruned will often result in no flowering and fruiting for at least one year, and maybe up to three years as the tree puts all its energy into restoring the missing leaf canopy.

Pruning too late in the season may also negatively affect flowering and fruiting. If a tree was pruned as it was getting ready to bloom, it is possible that branches that were set to bloom were removed.

▪ What is your irrigation schedule? If a tree is watered too often — more than once or twice a week — it may not bloom or set fruit. Too much water can suffocate the roots and cause root rot, or it may spur the tree to grow leaves rather than bloom.

▪ What is your fertilizer schedule? Too much or too little of the nutrients a tree needs can also disrupt flowering and fruiting. Too much nitrogen will cause a tree to grow leaves instead of blossoms and the tree may not be able to settle down to get ready to bloom. If the tree is not getting the elements it needs, it may be too weak to bloom. I will often ask if the overall color of the tree is good. If it is, then the tree is most likely getting all the nutrients it needs.

▪ What do you see at the base of the trunk? If the client sees mechanical damage from multiple string-trimmer hits or if the tree is planted too deep, these factors also will contribute to the tree not being healthy enough to bloom and set fruit.

After asking all of the above questions, I see which category the client is deficient in and prescribe the correct remedy. A tree planted from seed, a tree not getting enough sun, or a tree that was pruned too hard are the three top reasons why a tree is not fruiting.

This story was originally published February 4, 2016 at 9:00 PM with the headline "In the garden: Why won’t my tree fruit?."