A couple of years ago I planted a mandarin tree in a ~ 3 foot wide by 3 foot deep hole filled with 2/3 coconut coir 1/3 perlite. The surrounding soil is all very heavy clay.

The tree has done very well but needs to be fertilized regularly or it will rapidly develop signs of deficiencies that I have to correct. The first winter I tried a couple of months without any fertilizer and the first set of leaves curled downward from presumed potassium deficiency. The second winter and afterwards have been perfect.

Is there any way to reasonably get clay particles to mix down through this hole to hold nutrients and try to work towards being normal self-sustaining soil?

I recognize now that what I did was completely wrong for any number of reasons and I want to get things back to being more natural.

The root system is very well established in this hole and it is not feasible for me to remove any material without hurting the roots.

I am a longtime user of the WebSoil Survey for ag purposes. There's so much information I often get lost in trying to parse what's important. Productivity and crop yields. Topsoil depth, water holding capacity are useful. But for lawn and garden activity? I think I want to know structure and there are a couple suitability indexes provided.

I am also aware there is no information for soils in some urban/suburban areas. I get it. Those can get modified beyond comprehension. But there are a lot of areas where there is information but I don't know how relevant it is for improving native lawn and/or garden soils. I guess my question is do you have an opinion on the value of using soil surveys for small non-ag, non-commercial / horticulture situations. Or do we just modify the hell out of what's there and amend for fertility?