Citrus plants can be a substantial investment, with mature specimens costing in excess of 100 euros (or dollars), so it is understandable that people would be compelled to take good care of their investment. But are those specialist fertilizers necessary, or are they marketed on the basis of the ‘fear factor’ of doing something wrong?
All plants need a wide range of nutrients, including trace elements which are naturally present in most soils – however this is not always the case, and plants grown in potting compost will usually need additional trace elements alongside the usual N-P-K fertilizers.
Soil pH is also an important factor, as this can ‘lock out’ certain nutrients, making them inaccessible to the plant and causing a deficiency, even when there is technically plenty in the soil.
This is the basis of all fertilisers, and NPK stands for the three major ‘macronutrients’ needed by plants: Nitrogen, Phosphorous, and Potassium (the K comes from Kalium the latin name for this element.). All plants need these in relative abundance, although the precise balance required will change somewhat from plant to plant and depending on the seasonal growth requirements of the species. Magnesium is also required by some plants in relatively high amounts for strong growth, so it is worth considering this for the faster-growing plants. Tomato plants for instance need quite a lot of Magnesium and Calcium to grow well and produce lots of fruit – this makes these nearly macronutrients for these plants, although other species will do fine with low levels of these.
We all need our Vitamins and Minerals, including plants. Citrus plants have particularly high demand for Zinc, Magnesium, Iron and Copper. All plants need these minerals to some extent, in addition to tiny amounts of Manganese, Boron, Molybdenum, Selenium and many others including even heavy metals like Nickel and Cadmium. These can be supplied with the addition of organic matter, especially Seaweed meal which has a pretty complete range of minerals.
Special Citrus Fertilizer
Although specialty fertilizers can seem a bit expensive (because they really are), they can also be worth the money if it, for example, stops your $100 tree looking awful or entirely passing on from the realm of living plants. Nutrient deficiencies can cause all kinds of problems including susceptibility to pests and diseases, and it only takes one deficiency to cause a host of problems. Complete fertilizers such as ‘Miracle Gro’ will be excellent for the majority of plants, but as discussed earlier, Citrus have particular needs for certain minerals such as Zinc and Iron, and the right pH (6.0-7.0).
A good Citrus fertiliser will contain the full balanced range of nutrients required to support healthy growth, and will have the right pH so it is definitely recommended.