In most cases you want a fertiliser with three key macro-nutrients: nitrogen (N), phosphorus (P) and potassium (K) to replicate the natural environment in which trees thrive.
Some tell tale signs you may need to fertilise a tree:
- Not much growth during the growing season
- Dead leaves or branches
- Smaller than normal leaves
- Yellowing leaves
- Darker veins on your leaves
- A soil sample shows missing nutrients
You can use organic or inorganic fertilisers to feed your trees. Inorganic fertilisers generally work rapidly and organic fertilisers can take longer to break down and release nutrients. If you use a slow release fertiliser you can fertilise at any time of the year because they are designed to slow down the release of nutrients and to extend the length of time that nutrients are available to the tree.
How to fertilise
Spread fertiliser over the entire root area – about 4m from the trunk of an established tree. Do not put fertiliser in the hole when you plant a new tree. It can burn and kill the tree. Instead, sprinkle slow release fertiliser over the topsoil covering the root area plus another 50cm.
Citrus trees need feeding in July, November and March with a specific citrus feeder. Spread over the entire drip zone – out to the widest of the branches. Add trace elements if you are seeing signs of nutrient deficiency such as yellow leaves, dark green leaf veins.
Fertilise annually after flowering with a complete organic fertiliser. You can also fertilise every month with a fruit fertiliser or seaweed.
Fertilising is generally not needed for natives. If you do fertilise your natives use a slow release fertiliser and use it sparingly to avoid burning the tree or shrub.