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It forms white textured bumps near the top of the root, underwater:

enter image description here

This also happened to a previous avocado seed I started, and when the plant died after about 12 months, I dug up the roots, and these textured bumps were still visible (but brown from the soil). Here is a picture I found on the internet of somebody else with a more advanced version of the same problem:

enter image description here

It's not where new roots form, I can say that with confidence after watching it for several months. I can scrape it off, but it leaves a pale mark, so I hesitate to do so without knowing what it is.

Is it mold? Or something else? And is it hurting the plant?

Thanks for your help!

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No one's answered you and there are several things I can pass along since I'm a "master gardener" - though that doesn't apply as much here as my experience. I have grown avocado trees from pits successfully numerous times. What you're seeing here, in my opinion, is mold. I suspect you're exposing the pit to too much water.

After removing all the flesh from the pit, preferably using your hands and then a cloth to avoid damaging the pit, rinse it thoroughly under warm water and wrap it in a damp paper towel and stick it in an open ziplock bag in a dark place. I don't recommend the toothpick method.

After 4 to 6 weeks, occasionally re-dampening the towel, you can bury the pit in a small pot. It may take a little longer than 6 weeks for the germinating pit, or seed, to be ready. You'll know it's ready when the root coming out of the pit is nice and strong and ready to hold the plant, growing at least an inch outside the pit.

Bury the side down that's where the roots come out. Leave about a third of the other side of the pit above the soil. Well drained soil, typically called "cactus blend" or "cactus soil," is great, although everyday "potting soil" will work alright. I don't recommend using fertiliser at all in the first year. The seedling digests the pit as it grows.

In the first year, I recommend using a pot just a little larger than is needed to hold the plant and its roots, possibly no more than 10 in tall x 5 in diam at the mouth if using a custom-made one or slightly smaller if using a standard-sized pot. This is necessary so that water will focus over the little avocado tree's roots well before draining well when you water it. Transplant it into larger and larger pots as it increases in size.

Anyway, there is sometimes soil between the pit and the little plant when you first plant it. You'll see what I mean. I don't have any growing right now to take a picture of.

Good luck.

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    Good detailed answer; if you could also suggest the type of soil/soil blend you have had success with, and also type of nutrient(if any) you may have added & quantity & when/intervals, container type & size, drainage, and watering guidelines, that would all also be helpful. – M H Aug 3 at 17:35
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    Thank you. Good idea. I added that to the original post in edits. – Jamie Watts Aug 5 at 8:23
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    Thank you for your comment, and for the excellent additional information :) – M H Aug 5 at 8:37
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    Thanks for your comment Jamie. For my specific avocado plant that already has this mold (from the toothpick method, as picture above, but with two weeks more mold and also a nice stem that can soon be planted), would you suggest that I try to remove as much of the mold as I can before planting, or just let it be so as not to harm the roots? – Animik Aug 5 at 15:17
  • I'm sorry - I left town for a family emergency and completely forgot about this post! Anyway my experience has unfortunately been that once mold shows up, plants don't generally survive. I could be wrong in this case. What did you try? It never hurts to try. – Jamie Watts Sep 4 at 1:33

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