Pat replied:
I noticed on my home farm where we had lots of old Eucalyptus groves that
nothing lived either under them or in them so I never tried using them in my
compost (we had lots of chicken manure, spoiled hay & unlimited sawdust). On
the
other hand, the leaves did rot on the ground so they theoretically would rot
in
a pile?
Speaking from the home of eucalypts [Australia] I can confirm that they will
not help in the compost. Eucalyptus oil is, as you may be aware, a good
disinfectant, as well as a powerful decongestant inhalant. They will
certainly slow oxidation, and we do not normally use them in compost. Where
they are added, they tend to break down very slowly, though often with a lot
of fungi at work near them - the leaves themselves are pretty water
repellant and so air and water are trapped around them. But a layer of such
leaves in a heap of better rotten material will remain a layer of undigested
black leaves for a long time. When we have filled a black plastic type bin,
and want to leave it for some time to rot away, a few shovel scrapes of
driveway runoff with eucalyptus leaf material makes a good cover layer to
exclude flies, etc. Eucalyptus bark and leaves make a good mulch, slow to
break down, and with all the tumbling bark strips, quite attractive, if you
like the style of the Australian native garden. But not a mulch for
vegetables or the like, probably some allopathic effect. I once bought a
load of 'compost' from the local recycling centre (it is illegal here to add
garden material to the garbage bin; loads of garden cuttings to 4 inch
diameter are accepted for recycling. The effect of this quite well aged
looking 'compost' was to cause small plants to shrink before the eyes,
almost - probably a combination of high ration of C to N, probably heaps of
other deficiencies, especially P, but also probably allelopathy. But it
obviously sells.
We have some eucalypts alongside our fruit orchard. Trees don't grow so well
under them. On the other hand, asparagus and strawberries do. This in good
deep soil, though. Grass will certainly grow under eucalypts with
irrigation (take the walk along main path of Australian National Botanic
Garden at http://www.anbg.gov.au/main-path/path.html - but the picture with
the grass is far from a natural looking environment).
I suspect that a major factor in Pat's groves may have been water
competition. Eucalypts, while an adaptation to our phosphorus deficient
soils, have been used in a number of other countries in revegetation
projects, sometimes with negative effects as they have in some situations
become overcompetitive, tending to monoculture without the company of other
Australian flora. The other reason why they will survive where other trees
will not is that over a long period, they have, as have other Australia
plants, adapted to survive fast moving forest fire (blackened trees produce
new growth swiftly), and their seeds do not germinate without fire, or
immersion in boiling water or sandpapering or a quick spin in a coffee
grinder. So in circumstances where many European-American forests will
vanish with fire or drought, a eucalypt forest will be rejuvenated.
Dominant in the natural forest landscape (to generalise for an area the size
of continental USA) is litter from eucalyptus bark and leaves, shed all
year, this litter being, in pre-human times and in Aboriginal traditional
land management (farming with fire), limited and reduced by regular burning,
lighter, more frequent fire having a refreshing impact on the environment
rather than infrequent very intense and destructive fires (an important
learning experience in the 'modern' management of Australian native forests
in recent decades - trying to exclude all fire leads to catastrophic fire).
Dennis
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