Problems with my citrus trees?
I have a mandarin tree that is 4 years old. It comes out in flowers but the fruit won't set. I mulch with cow and horse manure also give them sulphate of potash and fish fertisler about every two to three months. How can I fix this gardening problem. Many Thanks Mervyn I live at Boulia and use bore water.
This article on lemon fruiting has some good tips that apply to your Mandarin as well. It's written for North America so adjust for the difference in seasons in the southern hemisphere.
The young age of the tree may be a factor, but I am most concerned about your use of manure. I recommend that you don't use raw manure for mulch or incorporation into the soil, because of the high nitrogen and salts, but compost the manure with other organic matter before using.
I prefer soil testing so that I know exactly what the mineral deficiencies are, and not guess with individual amendments, which can throw off the overall mineral balance. But testing is hardly worth the expense for one tree.
It's hard to go wrong with fish fertilizer every two or three months, and the potash is good.
You should consider adding bone meal for the Phosphorous and Calcium, which helps with flowering and fruit set. Gypsum provides Calcium and Sulfur. And epsom salts is Magnesium and Sulfur.
But of course all this depends on appropriate amounts of each. Another good way to go is a slow release COF (complete organic fertilizer) that is formulated for citrus.
Here is an example and you may be able to find something similar in Queensland or from an online source like Amazon.com
Water management is vital and drought stress could lead to failure of the tree to set fruit. Water deeply and infrequently to avoid over-wet conditions and crown rot. Once a week and then let it dry out some before watering again. If in the ground, try to achieve 10-inches / 25-cm or more water infiltration into the soil profile.