Citrus trees need a variety of nutrients to grow strong and healthy and produce lots of tasty fruit. Although there are many varieties of citrus trees, their needs are about the same: nitrogen, phosphorous, potassium, sulphur and calcium. Nutrients that are required, but needed in less abundance, include iron, zinc, magnesium, copper, molybdenum, manganese, chlorine and boron. Creating homemade citrus fertilisers is possible if you keep an eye on which nutrients the ingredients provide.
High in Major Nutrients
To create citrus tree fertiliser that is high in potassium, phosphorous and magnesium, fill a glass jar with leaves, stems and flowers pruned from the comfrey herb. Pack the material into the jar firmly and fill it with water. Allow the jar to sit in the sun for a full day to ferment. Strain out the herbs and use the water to fertilise around your citrus tree. This can be done on a monthly basis.
High in Minor Nutrients
To fulfil a citrus tree's requirements for minor nutrients, utilise parts of the stinging nettle. Wearing gloves, stuff a glass jar with the leaves, flowers and stems of the stinging nettle, packing them tightly into the jar. Fill the jar completely with water and place it in a sunny area for a day. Strain the herbs off, again wearing gloves, and use the liquid as a ground fertiliser for your citrus trees. This, too, can be performed monthly.
General Tree Fertilizer
There are certain nutrients that all trees, including citrus trees, require to thrive. The Westside Gardener website offers this recipe for a general organic fertiliser: combine four parts seed meal, one part dolomite lime, one-half part bone meal and half part kelp meal. Mix the ingredients thoroughly. Apply approximately 0.454kg. of this fertiliser on the ground around a small tree, increasing the amount of fertiliser for larger trees.