Annual mulching leading to excess nitrogen?

Hey folks. Just about every Liberty apple I’ve picked this year has shown a bit of water core. It’s not ruining the taste, but I read it’s possibly due to too much nitrogen. Would my annual mulching of my clay soil be the cause of this issue? I haven’t tossed down any nitrogen outside of mulch this year throughout my plants.

What are you mulching with? Most mulches, like wood chips aren’t nitrogen rich and are rather carbon rich, so would tend to bind up nitrogen in the short term during the decomposition process.

Usually hardwood, cypress mulch stuff. Nothing special. Is there anything else that might cause water core issues if that isn’t that cause?

I read that it can be caused by other factors: Watercore is promoted by large fruit, high leaf to fruit ratio, high fruit nitrogen and boron, low fruit calcium, excessive thinning, high light exposure, …

So any fertilizer should be low N. Most people use a 10-10-10 (NPK) balanced fertilizer each spring, you may want to apply a 5-10-10, and use plenty of dolomite lime or some wood ash to bring up your calcium levels. A soil test prior might be advisable, before you fertilize, to see what your deficiency may be. I am certain that mulch will not cause high N. Just be sure your mulch does not come within 3-4” of the trunk.
Kent, wa

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wood chips eventually become nitrogen rich as full decay involves multiple fungal and bacterial steps. It is the bacteria which fix nitrogen onto the decaying matter. so in my opinion yes.

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Watercore seems to coincide with high brix so I wonder about the claim that high N is the cause- can you provide a link if the claim is based on research- I’m just very curious because it seems counter-intuitive to me. I’ve read that the Japanese prize Fuji apples with water core because they are the sweetest, and I find that apples with it tend to be delicious myself- the main problem is supposedly that they don’t store well.

In answer to your question, glib is correct and of course he is. High OM soils always contain more slowly released N that can become excessive. When the mulch breaks down into humus, no matter what it’s original C-N ratio, it releases N- and more so when you don’t want bearing age fruit trees to have it- when the soil is warmest in summer, which inspires vegetative growth.

For this to happen enough of the mulch has to have broken down into humus and even before that happens, mulch increases available water, but mulch and a couple inches of black humus increases available water much more- at least where it rains a good deal during the growing season. At some point, more water means less sugar if it is available to trees in 2-3 weeks before harvest.


I too find apples with water core sweeter, and I love them.

High nitrogen levels have been linked to increased watercore incidence,
but the relationship is not clear-cut. There is some indication that high
nitrogen and low calcium may be important in watercore development,
but conclusive data are lacking.

This is from this paper that includes a lot more info about possible causes of water core. It is known that apples with watercore are especially sweet and the reason is explained here.

My guess is that the nitrogen that could lead to watercore is that absorbed during spring that tends to encourage larger fruit and that summer N might have the opposite affect, creating conflict in the research. Just a guess, but big apples seem susceptible to a lot of issues less prevalent when crops of same varieties consist of smaller fruit, including corking and rots. .