Plant
Doctor Archive
Arsenic
damaging garden?
Earlier this year I decided to raise my vegetable garden by 40 cm.
I did this by using H4 treated timber. Despite large amounts of
natural manures and compost the soil is dead. This I attribute to
the ARSENIC in the treated timber. There seem to be no worms or
micro-organisms , and the soil is not friable and has green algae.
Moisture also will not drain through it.
 I
asked the advice of Reg Lewthwaite, one of our horticulture lecturers,
and an expert in both toxins and compost. Reg said:
I have seen many gardens
growing in raised beds which were constructed with treated timber.
There might be human health questions about arsenic, but it has
never been a problem with plant growth.
The reasons plants might
not do well include:
1. The compost being
too fresh. Composts (including animal manures) which are fresh are
still in the process of breaking down. During this phase the soil
bacteria use up the free nitrogen in soil. The plant can't get enough
nitrogen to grow. The solution is to wait a while before planting.
Some composts release
high levels of toxic chemicals during breakdown.
These disappear as the
compost matures. The answer is to wait until the compost is mature
before planting out.
2. Too high a proportion
of compost to soil. Compost should be mixed with soil — not
be the main ingredient. I have inspected vegetable gardens where
plants have been killed by growing in pure compost. The reason is
that as the compost breaks down it releases nutrients. In a pure
compost these can get to a toxic level and damage roots.
The answer to this is
to mix in more soil or to wash out the nutrients with a heavy watering.
3. Another reason develops
from the last comment. In dry conditions the plants have to fight
to get enough water. Make sure the plants are fully watered in dry
conditions.
 Advice
by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor
of Resource Management.
Reproduced
with permission from NZOOM Home and Garden content,
from the previous
website of 
The views expressed here are not necessarily those of the RNZIH
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