Chilean guava - new growth, yellow leaves

[ChingfordHarry]

hi

I put a Chilean guava in a half dustbin last year, and noticed that all the new growth has yellow leaves (original growth is dark green, which is what "it's supposed to have".

From what I've read, it should be tolerant of an alkaline soil (which is what I have in North east London), but am I expecting too much, and should I try to remediate the situation?

i have a couple of blueberries in adjacent bins (same soil) that are a year older, and these also had small yellow leaves rather than the large dark green ones that most people would expect until I gave the soil a dose of vinegar followed by several doses of flowers of sulphur (the plants are looking really healthy now in spite of the summer we've just had.
however, just because something appears to have worked for one species, I wouldn't expect it to necessarily work for another that has symptoms that look the same.

thoughts?

[ChingfordHarry]

Oh - it's Ka-Pow...

[ameno]

I have one of those and new growth is meant to be reddish-tinged, so if the new leaves are yellow then it is definitely suffering.

Usually in plants when new growth is yellow it's a sign of iron deficiency. This may be caused by the soil being too alkaline, or it may just be general lack of iron in the soil (if it's garden soil, it's more likely the former).
To start with, I would try to get hold of some iron sulphate, and make a 1% solution of that (2 teaspoons in 1 litre of water) and use it as a foliar feed, spraying all of the leaves until they drip. Spray twice, one week apart, and you should see improvement fairly quickly (they'll start turning greener within a week of the second spray at the outside).
If they don't turn any greener then it's not an iron issue, in which case I don't know what to suggest.
If they do turn greener, you know iron is the issue so next you want to test the soil pH in the pot (unless you already know it, of course). If it's more than 7 you want to try and bring it towards 7 (making it actively acidic likely isn't necessary; neutral should be fine). Use your flowers of sulphur for this, but don't add too much all at once. You can also use iron sulphate, which itself is acidic, and this does bring faster results, but since it's water soluble it also washes out quickly so those results don't last as long as sulphur. Never use vinegar, and it's very easy to add too much and damage the plants, plus it washed out even quicker than iron sulphate, so any results are very short lived.
You will likely need to add more sulphur every couple of years. To your blueberry, too.

[ChingfordHarry]

Very helpful, thanks. Since the soil is based on London Clay, which I believe gets its (oxidized) colour largely from iron (interestingly, when dug out of deeper deposits London clay is blueish; I'd guess that the colour change is due to ferrous ions oxidising to ferric on exposure to atmospheric oxygen), I'd expect the soil pH to be involved here rather than lack of iron per se. since Fe(III) compounds tend to be very insoluble in alkaline environments (high pH) but more readily soluble in acid, I'd think that lowering the pH would help availability.

Using the blueberries as bellwethers indicates that reducing the pH is helpful, but I'm aware that they like their soil to be considerably more acid that most other plants (at least, those that I'm interested in growing) so what's right for them could conceivably pickle almost anything else!

I'll take a sample of the "growing medium" and do some testing this afternoon.

i have a half kilo bag of sulphur for dosing the soil in the half dustbins. That should last me for a few years...

[ChingfordHarry]

Quick update on this. The leaves are now a lovely dark green - they have been changing from yellow quite slowly over the months since I first posted. I suspect that our summer may have had something to do with this.

i tested the acidity of the soil in the ground around my half-dustbins, and it turned out to be ~6.5, so definitely on the acid side of neutral.