Rudy Poglitsh e-mailed from Swaziland with a question. “I have a problem. We have about 18 avocado trees in the ground. Almost all of them are over five feet tall. The soil is very poor, and the leaves are a pale green/yellow. We are headed into the cold, dry season. I want them to survive and thrive. We have previously made a fertility hole and put fertilizer in it, but my wife Ruth explained I put it too close to the tree (inside the drip line). What can I do? I really want these trees to live a long time and put out lots of fruit.”
Dr. Martin Price responded, “The first thing I wonder is whether it is a lack of fertility or if nutrients are being tied up because of pH imbalance, caused by very alkaline or acidic soil. If it is just a matter of fertility, then simply adding enough fertilizer (in the right spots) should correct the problem.
“I have had a lot of problems myself with one of my two avocado trees. ECHO’s farm manager, Danny Blank, told me I was not using nearly enough fertilizer and that I needed to mulch, mulch, mulch. (I don’t know if you saw the article Danny wrote a few years ago called “A Fresh Look at Life below the Surface” in EDN 96.An international scientific organization in Thailand actually adapted and reprinted it as a chapter in a book they published. You can download it from our website.)
“If it is a pH problem, that can be expensive to change. Again, mulch can help, because an acidic or alkaline soil will not affect the pH inside a thick mulch layer on top of the soil. Eventually fine roots will develop in that mulch.”
Tim Watkins, Nursery Manager at ECHO, also commented. “Can you describe ‘pale green/yellow’? Is it even, consistent color, with no sign of veins? Even light green could indicate nitrogen (N) deficiency, while obvious veins would indicate something like iron (Fe) deficiency…maybe resulting from high pH, like Martin suggests….How is the drainage of the area? Poor drainage or really heavy soil can also result in stunted avocado trees.”
Rudy wrote back about a month after sending the first note. “Our avocado trees are much improved. We dug trenches beside them on the uphill side and put grass and ash (to raise pH) in the trenches. The older leaves are better, and the new growth is the normal color.”