Restore Health to Old Macadamia Tree

Question from Bruce:

Just bought a property near Grafton
It has a well established macadamia
About 20 feet high,loads of fruit
The tree is looking a bit pale and i would like to take the top out and give it afeed.
Iran a citrus orchard for 5 years,could this tree be suffering from a magnesium defincy,also what would be a good pnk racio Bruce Bailey

Answer from Pat:

Fertilization and water requirements of macadamia’s are far different from citrus. Citrus should be watered deeply and infrequently, macadamias can accept any amount of water as long as drainage is good. Citrus are heavy feeders, but macadamia trees are members of the protea family from Australian and as such they are light feeders. As my book states on page 122, the exact fertilizer requirements of macadamia trees are not known and overfeeding can actually harm them. The safest way to fertilize macadamia trees to mix 5 Tablespoons of fish emulsion into 5 gallons of of water and sprinkle the solution under the tree twice monthly during months when the minimum temperature is over fifty degrees Fahrenheit.

If you wish to lower the tree by pruning, do so gradually over a period of at least three years or even longer, always cutting back to a side branch and making sure to leave adequate leafy foliage to shade the trunk and fruit. Cutting back hard will result in leafy re-growth at the expense of fruit.

If the tree is looking pale and loosing some leaves and twigs but has “loads of fruit” it may be that the tree is in decline and fears it might die due to neglect or drought. Lack of water, mechanical damage, or general neglect might have caused some surface roots to die. (Macadamias often need more irrigation during hot weather, which might not have been done.) If this is the case, you can save the tree and encourage roots to regrow by pruning lightly all over to encourage vigorous growth, then watering well and fertilizing as I have suggested above. Additionally,—and this is important—apply the fish emulsion solution as a foliar fertilizer by spraying all over the foliage in the evening or early morning twice a month for several months. Also, apply fresh mulch over the roots. It may take a few months or even a year, if the tree is in really bad condition, for your macadamia tree to grow new roots and to bounce back to health.

Read the label on the fish emulsion to make sure it does not contain added phosphorus, and always be careful to avoid fertilizers that contain high amounts of phosphorus, since Australian plants do not like phosphorus. (As I stated above, macadamias are Australian plants and since there is little phosphorus in Australian soil, Aussie plants do not need phosphorus. In fact, heavy applications can kill them. If the former owner did not know this they might have been over-feeding or feeding with a “balanced” fertilizer, such as 14-14-14 containing too much phosphorus for the happiness of a macadamia tree or any other Australian plant.)

Another possibility might be lack of trace minerals, as you have suggested. If older leaves are yellow with dark green veins, this is chlorosis due to lack of iron, zinc or other trace minerals, which I am sure you already know from your experience with citrus. Treat with chelated minerals or, to be safe, do a soil test first to determine the problem. Even without a soil test, an application of John and Bob’s Soil Optimizer might cure the lackluster problem and should help stimulate root growth. Another suggestion is to treat the ground under the tree with kelp meal or liquid seaweed emulsion. Either one of these is a safe, organic method of providing trace minerals.