Fertilizing Over Mulch (Specifically Apple Trees)

Question

I had a question and couldn't find the answer on here.

I have apple trees I've been struggling with for a few years now, between deer, caterpillars, and other things. I've got recommended fertilizer rates and times of the year, depending on their age, from the growers I purchased the trees from.

The question I have is about fertilizing them I have mulch down. I've had some people recommend pulling mulch back, fertilizing evenly, and putting the mulch back in place. I've heard others say you can put it in a ring around the outside of the mulch and it'll seep in to the roots. I've also heard that you can scatter it right on top of the mulch and it'll be fine.

I want to know which of these is correct or if all of them are. My inclination is to say that I just add the fertilizer to the top of the mulch and water it right after. I feel like it'll travel right through the mulch to the roots, just like rain water does. I think pulling the mulch back would potentially disturb roots and I think that putting a ring of fertilizer around the perimeter of the mulch might burn something. Let me know what you guys think. Thanks.

Also, this is just a regular balance granular fertilizer. I don't think it's slow release. The mulch is wood chips, 3-4 inches deep and 6 inches around the tree base. The recommend fertilizing (3) times a year at the end of March, beginning of June, and the end of August here in SC. I think it's something like a half pound for every year old it is, not to exceed a certain number of pounds. I'm pulling that number out of my hat, though. I have it written down somewhere, I just wanted to give you an example of how I'm doing it.

Answer 1

As you've noted there are differing opinions on this subject from reputable sources which likely means that all methods work, though one would think that direct mixing into the soil would be the most effective. Some people also advocate making drills into the soil and placing the fertiliser at equidistances along the drip line. If you have an orchard of trees, then it's likely you're not going to bother pulling back any mulch as it may be too time-consuming. Some fertilisers say that if you're going to apply it over a thick layer of mulch, then you need to double the amount applied.

Wood based mulches placed on the surface of the soil don't take up significant amounts of soil nitrogen. Their decomposition is primarily by fungi whereas nitrogen drives bacterial decomposition. But if you mix that mulch into the soil it will tie up some nitrogen presumably as the decomposition elements change until the process is complete when it's released back into the soil.

It's thought that soil fungi can form a bridge with their hyphae to reach the surface mulch and transfer small amounts of surface nitrogen to those parts of themselves feeding on the mulch.

Answer 2

You've said its wood chip mulch - if that's fresh wood chips, it will be stealing nitrogen as it decomposes. The fertilizer, if its granular, probably takes around six weeks to break down, releasing nutrients gradually as it does so. Were they my trees, I'm afraid I'd rake off the mulch, gently - if you find root material penetrating the mulch, then you'll have to stop, but assuming you don't, rake it off, apply the fertilizer, then immediately reapply the mulch over the top. No need to turn or dig the fertilizer in if you put the mulch back. Alternatively, I'd choose a liquid feed, applied over the mulch, more often.

You could choose to simply rake off the outer ring of mulch, apply the feed there, and then replace that, but I'd still choose the most difficult method, sorry! Others will probably have different ideas...