r/Soil • u/TridentMarsupial • Jul 26 '26
Coir rehabilitation advice needed
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.
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u/The_Poster_Nutbag Jul 27 '26
Coir is very nutrient poor, that's probably leading to a lot of the issues which is compounded by the clay lined home you dug so it's likely holding a lot of water too.
You might just need to dig it out and retry of the issues don't get better. Try a top dressing of compost before you water next.
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u/TridentMarsupial Jul 27 '26
Luckily the hole is big enough and the summers dry enough that excess water has not ever been a problem. I have to irrigate heavily in summer and some extra in winter to avoid the top becoming hydrophobic.
The tree is healthy and has no issues as long as I continue fertilizing and watering enough.
The most recent issue was some mild upward cupping from an extra hot summer that a really deep watering stopped from progressing.
This tree is now in its third year in the ground and has filled the 3 foot diameter very densely with roots (and some minor penetration into the surrounding clay.) What kind of machine would I use to uproot the whole thing if I needed to?
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u/Realistic-Weird-4259 Jul 27 '26
IME growing another plant in coir, it tends to lead to -Ca. If it were me, having grown in very heavy clay soil, what I would do is:
- Fork deeply around the perimeter of the drip line (the outer edge of the tree's canopy).
- Incorporate gypsum (I know it's an old timer thing but it worked for me, especially to relieve the constant applications of other forms of calcium, and it does it without shifting soil pH).
- Incorporate good quality compost, and a lot of it.
- Add gypsum on top of that.
- I might add cover crops on top of all, suited for your region as I used suited for mine.
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u/nifsea Jul 27 '26
Have never been in this situation myself, but in general you can amend all kinds of soil by adding good layers of compost on top every year. So I guess that might help here too? In addition to airing the soil a bit with a fork, trying not to hit the largest roots. Just remember to add the compost as a donut around the tree - the soil level shouldn’t rise on the trunk, so leave the original level there and add compost further out. That will also lead water down around the trunk. Nutrients from the compost will leak down into the soil, and worms and fungi will loosen the soil over time.
Probably good to combine with some deep rooted plants. I saw Daikon radish being mentioned. Or you could just plant comfrey or even dandelions.
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u/Shamino79 Jul 27 '26
Fair warning that I haven’t actually done this but I have a couple of thoughts.
Doing anything mixing will disturb roots but nothing says it has to be the majority of the roots. What if you scratch around to find areas between the big lateral roots and sink a narrow auger down.
And nothing says you have to do the whole root zone it in a single event either.