Diagnosing Brown Leaves on Lychee – Fertilizer Burn?

What is Fertilizer Burn?

The phenomenon known as fertilizer burn results from oversalting your soil relative to a given plant's needs and, more importantly, sensitivities.

Fertilizers contain inorganic nutrients, typically Nitrogen, Phosphorus, and Potassium (NPK), in various concentrations. The recommended percentages can vary from tree to tree as some are heavy consumers of one (say, Potassium), and others could be sensitive to another (say, Nitrogen). As such, there is no one-size-fits-all fertilizer for every tree out there- you should select your fertilizers on a tree-by-tree basis.

If you apply a fertilizer that is not balanced for your tree's needs, one (or more) of the nutrients it is sensitive to will not be absorbed and instead build up in the soil. As concentrations of any given nutrient rise, the buildup could prevent your tree from absorbing water, damaging the roots in the process. When this happens, leaves dry out and turn yellow and brown—particularly at the tips.

Some trees can recover from this if caught early. Others may die if left too long. As such, if your tree is experiencing fertilizer burn, it is an issue to address with some expediency. 

We believe this happened to our lychee tree when we assumed our standard citrus tree fertilizer mix would work well. What we did not realize, however, was that lychee is incredibly sensitive to Nitrogen, and our initial loading of slow-release fertilizer with high Nitrogen content likely overwhelmed the plant.

Throw on the fact that we were using city tap water, which also has minerals in it (plus perhaps some chlorine and fluorine, which the tree is also sensitive to), and we are likely further stressing the plant with each passing watering- adding nutrients from the water and the slow release fertilizer. Whoops.

The leaves started to turn brown at the tips, the tree dropped about half the leaves (something we originally misidentified simply as transplant shock after arriving), new leaf buds also browned and died off, and we were in panic mode to recover and prevent an untimely tree death.

What to Consider if Your Lychee May Have Fertilizer Burn

Before we repotted our new lychee tree, we must admit we did not fully understand how sensitive these trees are. This was 100% on us. 

To put it bluntly, young lychee trees are incredibly delicate to non-ideal conditions, but only knowing this in advance is your life easier. They do not like to be fertilized to a great extent when young. They do not tolerate tap water nearly as well as rainwater, distilled water, or reverse osmosis water. They are sensitive to wind. They need a period out in the cold (but not too cold) to fruit. The addition of Mycorrhizal fungi helps nutrient absorption, too.

We could go on.

In fact, the standard recommendation for young lychee trees is to plant them in free-draining soil, water with rain water or reverse osmosis water a few times a week (keeping them adequately watered but not waterlogged), and be careful on fertilizing the tree before it is established and with the proper NPK balance.

But let's say you didn't know this until later, and your tree has leaves with brown tips- what do you do?

First, take stock of everything you have done (or didn't do) to the tree that may influence this change. Improper fertilization could be just one of many reasons why your leaves are turning brown.

Have you been watering regularly? If not, it may not be an underwatering issue. Has your drip pan been full of water? You may be watering the plant too much and causing root rot. Did you fertilize, particularly too aggressively or with an inappropriate fertilizer? If so, this could be a fertilizer burn issue (likely our case). What about the water source? If it was tap water, that may be an issue when rainwater or other low-mineral water sources are preferred.

Second, inspect the tree to see if any other issues are present.

Pests in the leaves (like mites) could also damage leaves to have such a discoloring- albeit perhaps slightly different looking than the browning we are discussing here. Likewise, pests in the soil could also destroy the roots similarly. A close inspection here may help you check a couple of boxes, although admittedly, some of these pests will be too small for the naked eye to see, so you're looking for tangential signs to indicate a pest problem.

Third, identify the issue you think may make the most sense.

If it falls into the first case, possibly being an under-watering issue or over-fertilizing, the steps you take could potentially be the same. If it is the wrong water source, consider switching. If you think you are overwatering and contributing to root rot, cut back your frequency until the soil is drier than usual in between waterings. Or, if you think it is pests, research this one further for potential solutions based on the specific pest.

Ultimately, the problem with brown leaves may not be fertilizer burn at all. But in our case, it most likely was- we were watering regularly but used tap water and added a decent amount of inappropriate fertilizer when we planted. The most logical solution was indeed fertilizer burn.

So, what can you do if this is your case?

Generally speaking, you have two options here.

First, flush your tree out with rainwater/distilled water/reverse osmosis water- pending what you can acquire easily. These waters are often relatively low in nutrients and will cause any build-up of salts in your soil to dissolve and be flushed away from the roots.

We did this by putting the pot containing the lychee tree in our shower and, over several hours, pouring a gallon of reverse osmosis water through the soil. The water would drip out of the holes we had drilled into the bottom of the pot and, we hoped, would pull out enough nutrients to more or less “reset” the soil to more favorable salt levels.

• The size of your lychee tree will dictate how much water you want to pour here. As ours was young, with a trunk about 1″ thick at the base, one jug seemed sufficient. This felt like it amounted to 3-4 appreciable waterings, but of course, we did not have any reference point to start with here.
• When pouring water, do not completely overwhelm the plant by dumping all the contents into your pot- treat it like a standard watering (or less!) and repeat every hour or so until you've used your set amount of water and the water has fully drained out.

This flushing could potentially start to correct any underwatering issues as well, as you are assuredly providing way more water than the plant could need- so two possible birds with one stone here with a good flush.

That said, I would not be surprised if this one works best for those who used liquid fertilizers over slow-release granular fertilizer, if only because a water flush may only remove soluble fertilizer—a slow-release grain may still release more later.

Second, especially if the water flush didn't work as expected, would be to repot the tree with fresh soil. This would assuredly reset the nutrients in the soil in one swoop, but you would also need to be careful to ensure that the soil choice is appropriate for your tree outright- replacing one bad soil with another will not do you any favors.

Ultimately, we had to do this with our tree as the water flush did not work out as well as we would've hoped. Sadly, our lychee ended up losing all of its leaves as we waited a bit of time before repotting. If we had to do this one differently, I would've likely repotted much, much sooner.

Finally, now you can wait. You have now hopefully watered your tree with the correct water choice and flushed out excess nutrients (or replaced the soil outright), and you are now playing a waiting game to see what the tree does next before figuring out your next move. 

If your tree is like ours, this will hopefully be enough to give it a reset and start sending out new growth in a few weeks!

• Note: Lychees also undergo dormancy cycles where they do not send out new growth. They may not lose their leaves like other trees in dormancy, but growth may slow or cease between cycles. As such, you may not see a change as quickly as you would with other trees- cycles could be upwards of two months or more.

Alternative Explanations of Brown Tips in Plants

Unfortunately, overfertilization is not the only explanation for brown leaves (on lychee trees or others). There are many options out there, with fertilizer burn simply being one of the most common for beginners.

Other options include the following (this list is written mainly with lychee in mind- other trees could vary):

• More yellowing of leaves could be an iron or potassium deficiency (more common in older plants than younger ones)
• Pests such as mites in the leaves or weevils in the soil could be nibbling away at your plant
• The tree may also have a disease, be experiencing too much cold, or too much/little humidity

As with most plant issues, there are many options to possibly explain the problem. Although fertilizer burn is often one of the most common with lychee trees and was likely the case with ours, that isn't to say it is the only one.

As such, this article only focuses on one corrective action that could help right your lychee tree. It may work. It may not. But keep an eye on it, monitor your conditions, and see what any change does incrementally over a period of days and weeks. 

That said, issues like this can also result in tree death, which is what our tree ultimately experienced. So, despite even the best efforts, keep in mind that replacing the tree outright may be the inevitable solution. 

Have you overfertilized your lychee tree and successfully nursed the tree back to health? What did you do? Comment below to share!