Question
Hi,
I live in India. I have orange and lemon trees grown in pot and are 1 year old each. I recently repotted these plants because I noticed the fading of leaf colour to yellowish-green with dark green veins on leaf. I added coco peat and compost to the new pot along with loamy soil. But still not healthy and no growth. Some told me its due to iron deficiency and others told me due to high pH. I dnt know wat exactly. If these are the case then what is the best organic source of iron? And how to lower ph using vinegar? Because here i can find only such things. If its due to other reason, Please help me, I cant see thew dying. I have grown these from seeds. And is it good to use neem oil to control pest?

Answer
Hi there,

Most potted plants, including citrus trees, do best if the soil pH is in the 5.5 to 6.5 range. This means that the soil is slightly acidic. (On the pH scale, 1.0 is highly acid, 7.0 is neutral, 14.0 is highly basic or alkaline). It is in this slightly acidic range that essential plant nutrients are more soluble and most available for plants to use. When soil pH is outside of this range, the plant cannot absorb the nutrients. If a plant shows signs of nutrient deficiency, check the pH first.

In my experience, the classic symptoms of nutrient deficiencies are due to improper pH, not lack of nutrients in the soil. If the soil pH is outside the proper range, all the fertilizer supplements in the world will not help.

If the water in your area is hard or has high mineral content, that may gradually affect the pH of your potting soil. Hard water is not good for plants anyway, so it is best to use filtered or distilled water instead.

As soil ages, it tends to become gradually more acidic. For older plants, check the pH periodically. The addition of lime to the soil will raise the pH to an acceptable level. The addition of sulfur or iron sulfate will lower soil pH if it is too high. I cannot possibly tell you what is available to use in your area to lower soil pH.

Neem oil is somewhat effective on some plant pests.

I have written articles on fertilizer and on indoor plant pests that I will email for free to you (or anyone else) who emails a request to me at [email protected].

Please let me know if any of this is unclear or if you have any additional questions.

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Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

Visit my website at: A link to HorticulturalHelp.com