AusBonsai

On one picture I can see a clear sign of the chlorosis sympthom; yellow leaf with green veins visible.

Maybe it is indeed your mix, which looks ok at face value, combined with your fertilizer regime. I would guess the pH would be low enough, but apparently it isn't or it isn't because of your fertilizer regime.

I was under the impression that with chlorisis the plant wouldn't just die. So I suspect what you see with the leaves dying is either fertilizer burn or some disease other than the common pests. Lace bug and spider mites damage looks different so that's not it so it probably is fertilizer burn, eventhough it looks a bit different from the burn I once had myself.

I would use peat in your azalea soil mix. It will drain plenty with the right amount of perlite and other gravel/substrates.
One more thing you might consider is impurities coming along with these minerals. If they aren't horticule grade, they may cause a problems similar to fertilizer burn. But since you fertilized yourself that's probably the problem.
You have 50% pine bark so while you are using a lot of substrate, minerals will still accumulate as if your plant was in soil/peat.
You can't fertilize as if it were a bonsai in substrate. Not sure this is what you did, but just so you know if you don't.
In fact, your azalea will be ok without any fertilizer because the decomposing pine will provide more than enough minerals for quite a few years.

One always has to be very careful with using fertilizer on azaleas. Especially chemical fertilizer. When an azalea is in 100% kanuma it's a bit different because that allows you to flush out most salts with aggressive watering.
Applying a bit of slow release fertilizer 3 times a year is good enough. Cottonseed meal and osmocote seem to be the most popular.

I want to stress this a bit more, not because I am so sure this is indeed fertilzier burn but in general. Consider the risk-benefit for when you think about fertilizing your azalea. Since not fertilizing will generally have zero bad effects, you have to be really careful that what you are about to do will do no harm. If you dilute a chemical fertilizer to 1/10th the recommened usage, it will still have minerals in there that the azalea can use.

If you want to be sure you can try posting the picture in the yahoo azalea group.

I've reread this post again carefully and agree with Glaucus that there are signs of fertiliser burn. This may not be straight nitrogen burn, but perhaps salinity burn, or a combination of both, which is why it doesn't look like the usual fert burn.

I agree with using dilute fertilisers for azalea, organic is safer, but you can use mineral fertiliser with care. I'm curious about the concentrations you have used. This might yield some insight.

I've not used powerfeed, and generally avoid using any product from seasol. So its hard to speculate what is in the product that may have caused your problem.

Excessive P causes leaves to turn red in color, but doesn't cause a marginal leaf burn. Salinity, nitrogen toxicity, ammonia toxicity will all cause a marginal leaf burn. Excessive watering causes magnesium type chlorosis and browning of the very tips of the leaves. I don't suspect thqat excessive watering is the problem, but careful watering is always a good habit.

I notice you are using 50% pine bark, at low pH this can cause manganese toxicity, certainly the recomendaton of pH 4.4 is too low when using pine bark as the major ingredient. For Glaucus, pine bark in australia is generally composted P. radiata bark, it is rresinous lignaceous material with little nutrient content, though hi in manganese. It lasts for about 2-3 summers before degrading. By itself it would not provide the nutrients needed for good plant growth.

I think it would be wise to do a pH test on your potting mix, of several different trees that have been affcted, and let us know of your results.

There seems to be a lot of recomendations for organic bio-stimulants and plant conditioners, these products will not make up for nutrient imbalances, or chemical or physical insufficiencies in your potting mixes. Changes to pH, air filled porosity, potting mix componentry, all effect plant health by causing plant nutrient deficiencies, or toxicities. The addition of seasol or any other plant stimulant will not rectifiy these problems. In reality, the efficacy of these products in large grained potting media, of mosly inert components is dubious at best. Much better to learn what the elements required for plant growth are and workout how to get them to your plant.

The presence of pests on your azalea generally suggests that they are not healthy and are suffering some kind of nutrient imbalance, azalea are fairly resistant to the pests you reference when truly healthy.

Paul

I will be testing PH and i will inform on some results. Thanks for all of your input, it is quality stuff.

I thought that low pH would almost never cause a problem for azalea and rhododendron. Some peat has a pH of 3.5. A pH of 4.5 should be good, not bad.
I have never grown azaleas in so much pine bark but I know some growers in other places sometimes use quite a lot. But they use Douglas fir or Redwood bark because they decompose slowly.
Maybe fast decomposing bark in warmer climates can cause problems. I think decomposing pine bark requites nitrogen.

But maybe it is actually the pine bark making the over-fertilizing worse by acting like a sponge collecting all those minerals. More than would be normal with the usual soil mix. Maybe over time too much fertilizer build up and that caused the burn. I am just speculating here.

Hi Glaucus

Manganese content of pine bark varies with species, I'm most familiar with Pinus radiata as that is what we mostly have here, but can be high in other species. Manganese becomes increasingly soluble in potting mixes a pH drops below 5.2, symptoms of toxicity are reduced growth, a chlorosis of new leaves (similar in apearence to magnesium deficiency, though Mg deficiency occurs in old leaves) black/brown spots will also form on older leaves with a yellow chlorotic halo about them. These spots are also seen on older leaves of plants suffering with waterlogging and is Mn toxicity due to bacterial activity.

Composted pinebark is used as a peat substitute, it has a better water holding capacity then peat, and also inhibits soil pathogens, it is much cheaper than peat and also has a better air filled porosity than peat.

Since peat has little or no manganese it doesnt ose a problem with its low pH. It is simply the amount of Mn that is found in pinebark that can become a problem at low pH.

I suspect the leaf burn may have occured because the fertiliser used was too concentrated.

Any inert mix without pinebark, such as akadama, perlite, diatomite, turface, gravel can have low pH without problems to the plant as there is usualy no real toxic elements about, however phosphorus may become deficient as it gets bound up with some other elements, mainly iron. Adding extra phosphorus to cope with low pH will also aid Mn uptake by the plant causing toxicity.

In ground soil, aluminium is the limiting element as pH drops, pH <4.8 causes Al ions to appear and these are very toxic to plants roots. This is not an issue in potting mixes as they do not contain aluminium, unless you are foolish enough to use alum to reduce soil pH.

So safest pH is about 5.0 for all plants, as this gives the best balance of available nutrients for the plants.

Increasing salt in mixes is really due to improper flushing of the potting mix on a regular basis, accumulation due to porosity is a myth, it doesn't happen. Insoluble salts will not cause increased soil salinty and do not harm plants, however soluble salts will accumulate if not flushed, and cause salinity effects; early wilting,marginal leaf burn, leaf drop etc. This can be overcome by flushing the potting mix every four days or so with lots of water. Salts will accumulate if you water with little run off. So for instance, if a pot holds only 70mL of water, watering with 69 mL will not provide any runoff. Any salts in the water will remain in the potting mix, watering with 500mL of water will dissolve any accumulated salts and leach them out of the pot. Of course it helps if your water has a low salt content in it to start with.

Regards

Paul

Hi guys.

I thought this to be the most relevant thread to post in.

One of my Azalea's is all of a sudden not happy.
It has a lot of yellowish leaves and just doesn't look too flash.
I'm concerned the PH level is not right and just bought one of these to test:

http://www.ebay.com.au/itm/80-strips-1- ... 1e7c4e0f23

My technique has been to soak my mix in some water for an hour (do I need to use distilled water in Melbourne?).
Then simply pop the strip in the mix.

The results seem to be around 6.5-7.

Can I use some household options to lower my PH - Vinegar? Coffee?

Note my mix has a bit of sphagnum chopped though it and consists of diatomite, zeolite, some basic potting mix with pine bark and a bit of chopped sphagnum.

P.S. Damian did you end up running any PH tests?

How are the Azaleas going?

My Azaleas are going fine.
I found the leaf drop and yellowing was actually just natural attrition of older leaves.

I didn't end up doing anything to raise or lower my PH in the end.

I have two at home, one is in a bonsai pot and the other is in a grow pot. The one in the bonsai pot is looking under the weather, whereas the other is still covered in rich green leaves.

Hi Everyone,

I 'think' I am faced with a similar problem with my saotome azalea. There are leaves that are faded in colour, where as some are a rich dark green they used to be, but with dark spots forming.
From what I have read in this post I'm thinking it could be high soil pH due incorrect fertilising. I've been using an organic powerfeed from Bonsaishop once a month (for about 3-4 months). I will stop this in future until I'm sure I know what the issue is. Is there a best course of action I can take to help it back to health (if it is unhealthy), or would simply stopping feeding for now be the best option?