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Q&A: Why won’t my mulberry trees produce fruit anymore?

Mulberry trees provide tasty fruit — as long as the plants are hampered by frost or overfertilization. (Submitted photo)

Q: I have two black mulberry trees that I dug up and transplanted in my backyard. Now they don’t produce much fruit. I’ve tried pruning with no luck. I had a few berries three years ago.

I fertilize them in spring with horse manure and then mulch with wood chips. Could there be a fruiting issue due to male / female trees?

— Mike from Berlin Center

A: Mulberries are great trees to have — as long as they are not planted near where you park your car. The birds love the fruit and their droppings from mulberry fruit can cover cars, patios and other surfaces quickly. The color stains concrete.

But, the fruit is wonderfully tasty.

There is no perfect answer to your question, but there are two things to look at which are the most likely culprits limiting fruit production on your mulberry trees. They are frost and fertilization.

Yes, there can be male and female trees. But mulberry trees can be monoecious as well — which is more common (male and female blooms on the same tree). If you have seen fruit before, you know you have a chance to get fruit again. So no worries here.

The main reason you don’t see fruit is probably frost. Frost can be tricky and unsuspected, as we don’t always pay close attention early in the season. You may see flowers, but if you cut the flower open, the ovary may be brown and dead inside.

I suspect the area where you transplanted the trees could be a frost pocket. Basically, the area could be lower than surrounding areas and cold air remains there longer.

To determine if the area is a frost pocket, pay attention to the grass when we start to get frosts in March. If all of the grass is white, it was a rather hard frost. When temps hover around 32 degrees, watch for areas where some grass is not white — and other parts are definitely white. These white areas are the frost pockets to avoid when planting spring blooming trees / shrubs.

This year, check blooms on parts of the tree to ensure you have viable blooms. Cut the blooms open from top to bottom. Take a look at the ovary (what will be the fruit) inside the base of the bloom. If it is green, you’re good.

If it is brown to black, the frost has killed the potential fruit.

Secondly, the issue could be fertilization. Mulberry trees thrive in poor soil conditions. In Youngstown, mulberry trees thrive and fruit quite well along streets and next to vacant homes. So overfertilization may cause issues and encourage more growth and less concentration on fruit production. You don’t need to apply manure each year.

I encourage you to do a soil test to determine the pH and nutrient levels.

To better understand frost/freeze damage to fruit tree flowers, go to http://go.osu.edu/flowerdamage.

To learn more about mulberry trees, go to: http://go.osu.edu/mulberry.

— Barrett is the Ohio State University Extension Educator for Agriculture and Natural Resources in Mahoning County. Call 330-533-5538 to submit your questions to the plant clinic. Live clinic hours are 10 a.m. to noon every other Thursday on zoom at go.osu.edu/virtualclinic.

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