What I'm showing here is typical for all my seedling plants. They all start off perfectly fine, but after 4 or 5 leaves, the new leaves become pale yellow colored. My guess is the first leaves get their nutrition from the seeds and after that nutrition has to come from the roots. I do fertilize my plants well, but, as I mentioned in another thread, the tap water, which according to the water company has an average pH value of 8, may be the problem here. Can anyone confirm the tap water can cause this kind of problem?

Tarocco seedling:


Sanguinelli seedlings:


I also have seville seedlings with the same problem.

Citrus are heavy feeders. Also that soil you are using looks terrible.

Try using a rich soil. Mix in some Osmacote & add a little Epsom salt in your water once in a while. I am not very scientific when it comes to my citrus, but what I do works.

The leaf symptoms look like an iron deficiency. An iron deficiency always show up on the NEW leaves of the plant, with green veins that have no additional green border area around the vein on otherwise a yellow leaf. The availability of iron to the plant begins to drop at pH of 6. So the higher the pH goes above 6 the worse the availability of iron. - Millet

In fact it's the same DCM Mediterra soil (for citrus trees) I've been using for years... I did loosen the top layer a bit, which is now somewhat dried out, but the soil underneath is still moist. I did apply epsom salt in early spring (not to these seedlings, but for instance to the ill-looking yuzu in my other thread) but it didn't improve the situation. I apply a good quality liquid fertilizer with every watering.

I will see if I can find some osmocote that is suitable for citrus plants. (now I know what thise little pearls are that are in the soil of newly bought plants! ). I'm also trying to find a source for pH- to lower the pH value of the tap water, but apparently such a product, which requires careful handling, isn't available in garden centers.

Finally I'm planning on getting a rain water tank, which is probably the best option...

Still, what baffles me is that, while some plants look ill, some others look perfectly healthy while they all get the exact same treatment!...

Mark wrote -- "while some plants look ill, some others look perfectly healthy".

Are these plants the same cultivar, or are these different type of plants responding to different situations? - Millet

No, they're all different varieties. I think it is safe to say that varieties with yellow fruit are the most affected. The orange trees hardly show any symptoms (with the exception of the seedlings). The tahiti lime, while not an orange citrus fruit, doesn't show any symptoms either. The same is true for the etrog, but I don't have the etrog for a very long time so that may still change. I do believe the rootstock has something to do with it also. Plants on poncirus look worse than the others.

To lower the PH of my water, I use a product called "ph down" made by Flora Hydroponics. It's just phosphoric acid. In 1 gallon of solution, 2.5ml of ph up will lower the ph of the solution by 1/2 of a "degree". Gallon of solution with ph of 7 + 2.5ml of ph up = solution with a ph of 6.5.

If you were going to use an iron supplement, I'd suggest Iron Chelate 6% EDDHA. The EDDHA form of chelation allows the iron to remain available to the plant in the widest pH range(3-10). EDTA and DTPA forms of iron are not plant available when pH of media or solution is higher than 7.

You can buy Iron Chelate 6% EDDHA from JR online as a specialty nutrient. Here's the link to the online store: http://www.jrpeters.com/Products/Specialty-Nutrients/Buy-Specialty-Nutrients.html. I see that they also offer a ph adjuster but I'm unfamiliar with it.

Best,

Skinn30a

I know about the pH down stuff but the problem is I can't find it very easily. The iron in the fertilizer I use is chelated, so that should be OK.

Today I contacted the manufacturer of the fertilizer I use, asking if they could somehow help me out. That's the advantage of dealing with a small company : one can contact the people behind it directly!
Like you mention, they told me that chelated iron remains available even at high pH values, but the plant will stop taking it up when pH gets too high.
They also told me that not only the tap water pH is too high, but the pH of the soil I use is too high as well. Their suggestion was to...
- use rain water if possible
- find a better soil with a suitable pH value, or
- mix the soil I currently use with peat to lower it's pH value

They can provide me with pH down (nitric acid) but this has to be used with great care as a little overdose may burn the roots and destroy the plants.

If you can get it, nitric acid would be ideal since it would add a little nitrate nitrogen.

Ask the fertilizer manufacturer what form of chelated iron they use in the fertilizer. If they are using the EDTA and DTPA forms that are not effective at a ph of above 7 then they are correct that the trees cannot use it. I use Iron Chelate 6% EDDHA on the in-ground tress that I have that are growing in soil with a ph of 8 and it works great.

Best,

Skinn30a

The primary rootstock influence is the rootstock's ability to supply water to the tree, the secondary influence is nutrient uptake. Invigorating rootstocks (rough lemon, vlkamer lemon, macrophylla) perform good at high pH and are better extractors of soil water and nutrients than less invigorationg rootstocks. Less invigorating rootstocks such as Trifoliate orange and many of it selections and some of its hybrids (citranges & citrumelos) are the opposite, and they perform poorly in high pH situations. - Millet.

skinn30a,
They use the DTPA form (whatever that is, I'm no good in chemistry... )

Millet,
My observation may be correct then. I know which ones use poncirus as rootstock. I don't know what the other rootstocks are though, except for the mandared which uses carizzo as rootstock.

Well there you go.... it makes sense that your seedlings would present an iron deficiency since DTPA is not available for uptake by the tree if the ph of the medium or solution is higher then 7. Only EDDHA will be available for uptake of the tree if the ph of the medium or solution is higher than 6.5...

Consider supplementing with Fe-EDDHA until you can figure out how to lower the ph of your medium to a ph of less then 7.

Best,

Skinn30a

Mark it should be very easy to collect rain water. You really don't need an "official" rain collector barrel. Any old barrel even a 5-gallon (21-22 L) plastic pail (or just about any container) will collect rain water. Rain water should correct your problem in just a week or two. The very best to you and your trees. - Millet

Without reading thorugh everything already said: I use the mediterra soil too for seedlings. I just add some extra perlite to it. I used tap water in the beginning and now mostly use rainwater. Never had a pale leaf so far.

I have just been on the phone with mr. Borms of Sunplant (the fertilizer manufacturer) again, talking about the EDDHA chelate. He confirmed that the plant will take up this chelate but still won't feel OK in a too high pH environment. It is better to address the problem fundamentally.
He told me to send them a sample of the potting soil. They will then test the pH value and the nutritional content for me and make some suggestions for improving the situation.
He also told me that applying leaf fertilisation may also help the plants look healthier.