GrantJohnPaterson
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Pot grown avocados - leaves rusted/ brown spots

Hello all: virtual non-gardener here.
We have three from-seed avocados in pots on a terrace in a hot (35-45C) climate.
One is showing rusted spots at leaf tips and edges, moving inwards on the leaf.
Some photos attached. Can any clever gardener here help?
Many thanks / Grant
potted avocado - rust on one.jpg

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applestar
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Location: Zone 6, NJ (3/M)4/E ~ 10/M(11/B)

If I am seeing this correctly, it’s the avo in the pot sitting on top of the soil in the big planter — which is empty? Those contorted sticks are dead?

- What was in the planter before? Is there any chance it had become diseased? If this is the normal placement, when you water, does the water from the affected avo’s pot drain onto the potting soil of the planter below? Is the bottom of the pot in direct contact?

— Barring possible disease like avocado rust —

...what I’m thinking is that if the planter underneath is not actually holding living plants, then you are allowing that soil to go dry, and the Avo in the pot sitting on it is encountering dry soil with roots, resulting in root-kill — this would make sense since the affected leaves appear to be lower/older on the plant.

...another possibility under same scenario is that fertilizer in the planter soil is wicking to the top and there is a higher concentration of salt or even salt bloom, which the avo on top is absorbing when watered. Salt-damage also tend to occur on older leaves.

— this is an example of me making up imagined scenarios at 4AM while waiting for the sun to come up. haha Please supply thorough and complete description of the environment and conditions. I do grow a lot of avocados from seed for fun, so I can imagine a lot of situations when brown spotted leaves can occur.


...avocado is deciduous and a certain amount of leaf-senescence and decay/drop is normal as well — are these the oldest leaves?

GrantJohnPaterson
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Many thanks Applestar. Hope you got some more sleep.
Observant of you: the big planter held a grapevine, which died over a year ago, I suspect from root rot. I haven't changed the old soil but added about 10kg of new potting soil from the top. The pot holding the avo does sit straight onto (and drains into) the old planter soil, but no root breakthrough. When I clipped the main trunk, we got four branches; one of those has rusted leaves, so seems not to be only the old ones.
The avo is in pure potting soil, around 5% mixed with sand and polystyrene drainage granules. In this Dubai summer (hot!) we've been watering daily, aiming to wet the roots but avoid constant draining out. We're pretty junk at growing things, but enthusiastic.
Cheers,
Grant

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applestar
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I still think it’s possible the salts in the old grape planter soil is rising to the top and leaching UP into the avocado pot. Are there any fertilizer salt encrustations on the soil surface or along the inside rim of the big planter? — Do you remember a chemistry lab experiment in which a strip of paper or cloth is suspended in a solution, and the minerals wick up to stain the wicking material with bands of different color?

Try flushing out the soil in the big planter.

...I actually arrange my container plants like this — stack smaller container on surface of larger —all the time. If the plant in the big planter dies, then I just plant something else ...with or without freshening the potting mix. Sometimes I end up using the available space in the big planter as convenient place to push some citrus seeds or other fruit seeds in. Then I keep watering and they eventually sprout.... and if I have forgotten to label, then sometimes they become mystery plants.... :oops:

Over the winter, I had a sweet potato sprout in the pantry, so I put it on top of the soil in a big planter. Fast forward >> I took out the pot a few days ago, trailing 4+ feet of sweet potato vines. It has an overwintered pepper plant and a cluster of mandarin orange seedlings in it as well. :lol: (I have to separate and repot, and plant the sweet potato in the garden :wink: )

GrantJohnPaterson
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Thanks again, I'll give the full flushing a go.
.. and throw some seeds into the big planter :)



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