Coconut coir is also known as coconut fibre; it’s the springy material you get from inside the shell when you husk a coconut. I had never heard the term before and had to look it up.

https://en.m.wikipedia.org/wiki/Coir

I wonder if this is the reason the GP has such luck with it. From the linked Wikipedia article:

> Trichoderma is a naturally occurring fungus in coco peat; it works in symbiosis with plant roots to protect them from pathogenic fungi such as Pythium. It is not present in sterilised coco peat[citation needed].

My experience is very different !

Coconut coir is a real pain and struggle to remove and separate from the roots when you need a transplant.

Likewise small plastic containers are way too small for growing trees especially from large and medium seeds like nuts or mangoes.

Ideally, you want to pick a really big one (at least 5 to 8 liters) with a preference for depth over width, to grant the tree more space to grow and not damage the roots. They are quite sensitive in the first year, and each transplant will slow the growth for 1 to 3 weeks.

Growth is driven by two things : environment (sun/water/temperature) and soil. The one you find in most gardening shops is fine, as long as it's not too heavy and doesn't contain peat (might be difficult for our North American friends). I switched to fine, light soil with mycorrhizae and wood fiber, with a greater success.

Fertilizer is completely optional in the first year, but if you add some, avoid putting it in contact with the roots.

Finally, trees grow stronger if they are kept without support under the assault of the rain, wind and sun. They are meant to resist and adapt to their environment, so you really don't need to add a prop to keep them straight.

This year, I'm testing different style of pruning. My intuition tells me that no-to-very-light pruning yields better development than the fast and heavy pruning you see in gardening shops.

PS: I've grown 30 trees from seeds on my small balcony.

sorry that you haven't had luck with the method I use, but glad you found a good one for your practice. I've been growing fruit trees in Florida successfully as I described for over 10 years and 200+ growths and grafts. (It's a great practically free hobby and make sustainable gifts) I've even sold several to the city and county. Different strokes for different folks.

I prefer heavy duty felt pots which have the advantage of "air pruning" the roots. Once you've seen the root system those develop you won't go back to anything plastic. Instead of just curling around the bottom of the container in search of the air holes at the bottom, the roots grow just to the pot walls and stop, because they get plenty of oxygen transferred through the felt so they don't continue on searching for it becoming root-bound - in all directions. One solid massive root ball. One brand name is "smart pots." They're reusable as well.

Edit: Hard to find a video that don't involve cannabis growing, but here's a decent one: https://www.youtube.com/watch?v=4GrnTSXsFKI

A burlap sack would probably work in a similar manner, but not sure how long it would last.

I bet the coir + felt pot would combine for some outstanding growth

I've found that if you don't transplant out of such containers very early, the root system is stunted. Instead, you can take two cardboard 1/2 gallon milk containers, cut the bottom off of one and stack them to make a tall tube pot. Fruit tree seedlings can survive in that kind of pot for 6 months to a year and then can be planted in the ground without disturbing the roots (you just dig the hole, cut the bottom of the bottom cardboard container and place in the hole, fill the hole with dirt, and pull the cardboard container off like a sleeve).

that's a great idea. The same cab probably be done with two plastic containers, with large holes in the bottom, cutting away the bottom for the roots. I like to reuse those containers whenever possible, especially since recycling in my area is pretty much ceremonial. I find that if you transplant out of the taller container by the time the shoots reach the lid, you're in good shape for the roots to take to a pot.

Peat moss is a good alternative as well and has most of the same properties you pointed out

from what I understand, it doesn't have the same anti-pathogen properties as coir.

I use gravel.