The majority of home gardens in Southern Australia have a few citrus trees growing to perfection. I know the vagaries of "Fruit fly" in the eastern states, make their growth less than trouble-free and many wouldn't bother growing citrus because it becomes a constant battle with insects. For those that grow them like weeds in the Mediterranean areas of Australia and even in the sub-tropical regions, you will soon discover that they have a few deficiencies which appear when growing in fairly alkaline soils. Alkaline soils are those with limestone in the lower profiles. In Mediterranean regions the soil profile generally gets more alkaline with depth, even if you mulch with acidic composts and leaf-litter on the surface.

The ideal conditions for most citrus are warm, frost-free sites on free-draining soils. On alkaline soils in the range of pH 8 - 9, citrus crops frequently develop lime-induced-chlorosis (LIC), which shows up on the leaves as a green vein pattern against a pale green leaf. This is a common condition for many native plants and acid-loving ornamentals for gardeners who work on alkaline soils. The problem is that although iron is often present in these soils, the high pH or degree of alkalinity in the lower soil profile, makes the iron uptake, very slow. The remedy is quite simple on a small scale, but extensive use of iron chelates has only a short-term benefit. More efficient and longer-lasting is iron sequestrine, but it is very expensive to use, on other than valuable container-grown plants. Just a word of caution. If you use iron sequestrine on container-grown plants, water it in over a garden bed because the liquid looks like a full-bodied Shiraz wine and it will stain your cement paths. Also of some use, is the fairly cheap "flowers of sulphur", but the sulphur needs to be added frequently. The organic ' solution' is to compost green matter and rely on the leaching of humic acid into the lower soil profile which certainly works, but most gardeners expect a quicker response.

An even slower solution that does make the soil more acidic over time and then results in the uptake of available iron, is to bury old iron filings or pieces of iron off-cuts under your orange, mandarin or grapefruit trees. As the iron oxidises, it makes the soil more acidic and renders the soil iron available to your citrus trees, but I stress that the process is a pretty slow one. Both organic and chemical remedies rely on warm soils and in winter and early spring even when the correct acidifying agents are added, they work very slowly. The message is, persevere with the problem until soil temperatures rise.

Another pretty common problem on alkaline soils is the lack of uptake due to the high soil pH of several minor trace elements, such as zinc, manganese and magnesium. Their lack of uptake by most plants would go unnoticed except that citrus have hungry appetites for nutrients and in particular, these three. The alkaline soils also make their uptake as difficult as for iron. Even when you add a complete citrus fertiliser to your soil, the presence of potassium locks these minor trace elements up, so that they are not readily available to your citrus trees.

That's why the experienced Riverland citrus blocker or Sunraysia blockies apply the minor trace elements of zinc, manganese and magnesium as foliar sprays, several times during the warm weather. Even this is not as straight forward as you would expect it to be. These three compounds cannot be sprayed at the same time, because they precipitate and settle out, thereby depriving your favourite navel orange of its due reward. The zinc, can be applied as zinc sulphate and mixed with manganese sulphate then sprayed in late afternoon on a day when no rain is expected for at least three days. After three or four weeks, the magnesium sulphate or "Epson salts" can be applied, also in late afternoon to reduce evaporation and applied when fine weather is predicted. To aid the uptake of magnesium as a foliar spray, nitrogen needs to be added to tepid water, usually in the form of urea, because apart from being fairly cheap, it contains a massive 43% water-soluble nitrogen, so you don't need to use much.

It all sounds a bit complicated doesn't it, but your oranges and lemons will put on lush foliage and flower prolifically as a result and of course set better quality fruit, so it's worth the effort.

While I'd like you to be able to diagnose the specific deficiencies on your citrus, I have to admit it's a lot easier to make the soil a little more acidic on alkaline soils, then foliar spray with the three minor trace elements.