I planted this pluot tree for my grandma a few weeks ago and made sure to paint its trunk to protect it from the sun; I hadn’t so protected a pluot tree that I planted for my mom eight years ago and look what happened.
I’ve seen a lot of trees in other yards and school gardens lately with this problem. Check your fruit trees; I hope you don’t find it, but check.
Effects of sun damage
The good news is that this damage from sunburn on the trunk does not usually kill the tree, at least not immediately nor if you can protect the trunk from further damage. My mom’s pluot tree in particular still grows and bears fruit although it doesn’t perform as well as the trees without damage that grow next to it.
My theoretical explanation for this is that the trunk now has less capacity for sap flow — for water and nutrients to flow up from the roots to the leaves, and for the energy that the leaves create to flow down to the roots. It is roughly analogous to pinching off some of the blood vessels in your legs; they’re still going to work but not as well.
Another effect of sunburn on a trunk is that it is attractive to certain pests. Borer insects sometimes show up to exploit the easy entry point into the tree. (Read more about tree borers on the University of California IPM website here.)
Which trees to paint
So I paint the trunks of almost all fruit trees that I plant nowadays. There is no downside to painting trunks, save the minimal money and effort it takes to do the painting.
Last winter, I planted this apple and painted its trunk:
Two winters ago, I planted this pear and painted its trunk:
Also two winters past, I planted this cherry and painted its trunk:
These are the types of trees that especially need their trunks painted: pluots, apples, pears, cherries, and plums too. What do they have in common? They are inclined to grow their branches upright, especially in their early years when they’re not bearing much fruit. These vertical branches provide little shade for the young trunk whose bark is thin and susceptible to the sun.
Another type of tree that is extremely sensitive to the sun in general and therefore often needs its trunk painted is avocados. I planted this avocado the other day and will be sure to paint its trunk as soon as this week’s rains pause:
On the other hand, I planted these avocados and found it unnecessary to paint their trunks because their lower limbs are shading their trunks well:
How to paint
There are a few expensive products that you can buy to paint trees, but I just use cheap white latex paint (interior or exterior, it doesn’t matter) and I dilute the paint about 50 percent with water. Many other people have done this for many years in many locations. It works.
Paint all the way down to the soil and all the way up to the lowest limbs on the south side of the trunk. It is the south-facing side of the trunk that usually gets sunburned although it can also happen to the east and west sides, depending on what is around the tree. So I always paint all sides except the north just to be safe. The sun never shines strongly from the north here in the Northern Hemisphere.
After initially painting a tree’s trunk, usually, the tree grows and bears fruit and its branches become more horizontal under the weight of the fruit. These branches then shade its trunk such that no later paintings are required. Here is a five-year-old pluot tree in my yard whose trunk I painted at planting, and which now has weeping lower limbs that shade its trunk:
If, however, a fruit tree doesn’t begin to protect its trunk from the sun like this, then that remains our responsibility. Grab the paint can, and get it done well before summer.
A list of all my Yard Posts is here.