have two 10-year-old macadamia trees, one of which is grafted.
This season the grafted one produced a crop of wrinkly shelled nuts
which were shrivelled and inedible. What is wrong with my grafted
tree which has been a reliable and prolific cropper until this year? What
is the fertiliser for these trees as I have been given contradictory
advice. (Fertiliser kills them this from a nursery
to "I use 50 tons of chicken manure on my 50 acres of macademias".) The
trees are growing in coastal clay/sand with reasonable drainage.
I cannot get chicken manure at present and have a large bag of sheep
are not usually attacked by pests and diseases (except rats and
possums!), so your wrinkly and shrivelled nuts are a bit of a puzzle.
It could possibly be damage from the green vegetable bug, which
will pierce the nut and make the kernal discoloured and bitter.
Insecticides are probably your best option here. Another possibility
is that your trees could have the wrong balance of nutrients.
Macadamias grow best
in free-draining soils full of rich organic matter, but will cope
with anything from clays to sandy loams, as long as they have adequate
drainage. As for the nutrients, a general fertiliser should
do the trick, but be aware that some growers consider that high
levels of nitrogen reduce the amount of nuts you will get (high
nitrogen often will make plants grow leaves rather than flowers
and fruit). There is some evidence that the trace elements
boron and zinc can help nut formation and development. Both
chicken manure and sheep pellets would provide a lot of nitrogen,
so depending on the levels you have in your soil, you may want to
I suggest you get soil
and leaf samples from your trees tested for nutrient levels.
Several companies offer this service in New Zealand.
You can get more information
from the New Zealand Macadamia Society, www.macadamia.co.nz
by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor
of Resource Management.
with permission from NZOOM Home and Garden content,
from the previous
The views expressed here are not necessarily those of the RNZIH