 Conference
1999
New Zealand Plants and their Story
From
Collection to Cultivation
Anita
Benbrook
Assistant Curator, Otari - Wilton's Bush
Wellington City Council, Box 2199, Wellington
Growing a collection
of plants within a Botanic Garden is a challenge to any gardener.
Otari's challenge is to grow as large a range of New Zealand's native
flora within one garden as is possible. If you consider the range
of habitats required from the Sub Antarctic Islands to the top of
the North Island and offshore islands, from extreme cold to almost
tropical. How is this achieved? I will attempt to describe to you
a few of our techniques that allow us to grow one of the largest
collections of New Zealand natives.
To complicate matters,
we also aim on having a large proportion of this collection from
a sourced location. The collection can then be used for scientific,
conservation or educational purposes.
This generally means
collecting plant material from the wild.
A true example of a species
is at its best when growing in the wild. Once brought into cultivation
it generally becomes easier to cultivate after the first or second
progeny. Whilst this is good for horticulture, it doesn't truly
represent the species. An example of this could be an alpine whipcord
Hebe. Brought down to sea level, the plants will often
open out from flattened or appressed leaves to tiny open leaves
all down the stems. This is not characteristic of the species. If
you then propagate from this material it will end up somewhat removed
from the original. The plants often end up growing too fast as well,
often flowering themselves into an early death. Sometimes you also
get the plants adapting to the local climate, and changing form
over time.
By careful selection
of plants and understanding their requirements you can grow them
successfully. Anyone can go and dig plants up but it takes more
time to study them and keep these plants alive in cultivation, and
propagate from them.
When we are renovating
an area or looking to start a new collection we will research the
plants from an area and organise a collecting trip. An example of
this would be collecting plants endemic to Marlborough in 1995 for
the new Marlborough collection.
We looked at regional
plant lists and worked out where would have the best representative
plants of that area and obtained the necessary DoC permits.
We restrict our collecting
to seed and small quantities of cuttings. We have found that by
collecting cuttings and wrapping them up in sphagnum moss then sealing
into plastic bags we are able to keep these cuttings fresh for up
to two weeks. We store the cuttings in a cool place, either in chilly
bins or in the shade until we can get them home. The seed are dried
out at night and packaged into small plastic bags and also kept
cool.
By far the most important
part of these expeditions is studying the environment that these
plants grow in and learning about the conditions that would be best
suited for planting them, if we are successful in growing them on.
Notes are taken on the altitude, aspect and fellow companions that
the plants associate with. This, I think is the most important part
of being successful when placing plants back at Otari. If you don't
know much about the plant then you have to rely on books or information
from other successful growers. This is all very well for popular
growing plants but when growing some of the more obscure parts of
the flora there is little information available.
Once arriving back with
the collected material, the cuttings are quickly processed, with
most being placed into a pumice-growing medium in our shadehouse.
I believe that with slight modifications of the media and the use
of plastic bags for higher humidity most of the flora can be successfully
propagated. Bottom heat and glasshouses would certainly speed the
production time of some plants but there is usually a good strike
rate without this. Again there is often little information about
some of these species so I work on the principle that most plants
will grow from semi hardwood cuttings. There are some exceptions
e.g., deciduous olearias, such as Olearia hectori, respond
better when propagated as hardwood cuttings.
Seeds are chilled for
a few months in the fridge, and then sown in a 50% peat/sand mix
with grit placed over the top of the seed. This is to retain the
moisture and slow the growth of liverwort. I think it also simulates
the alpine environment. I usually relate where the plant has come
from and ponder how the seed would naturally have been dispersed
and what would cause it to germinate. If it is an alpine wind blown
seed then perhaps it would land on a shingle bed and be worked into
the gravel by rain, wind or frost where it is then sheltered and
can proceed to grow in the spring.
Once the plants have
grown to a reasonable size and have survived the nursery treatment
they are ready for the harsh reality of public life.
My philosophy here is
quite simple for some plants. If it comes from a warm northern area,
it is placed with a northern aspect of a nice warm frost-free slope.
If it is a southern, cool loving plant then a south side of a border
is sought. This of course has its limits as when growing all the
Pittosporums in one garden bed, you only have so many northern or
southern positions, and what about the epiphytic Pittosporums? Pittosporum
cornifolium was first planted in rock crevices, and grew well
but tended to get too much sun, next they were put underneath some
larger trees that were representing their host tree. They now have
a fairly dry position, dappled light and are growing well. This
is through thinking about their natural environment.
Now lets turn to a tricky
plant, Cordyline indivisa or mountain cabbage tree. You
will find that some gardens will have no problem at all. For example
in Wakehurst Place in England I saw them growing very happily in
a garden bed, probably because they got quite cool air for most
of the year and were fairly shaded at times. We have struggled constantly
to get beyond about 1 metre with ours. We have tried open positions,
failed; in the wild garden grew well until it was stolen; tried
in a free draining soil in a shady position, got phytophthora, a
root wilt disease. I went back to the basics and thought about where
I have seen them growing in the wild, sometimes on the side of cliffs,
exposed to wind, usually in very free draining, but moist cool positions.
This time we are trying
on the side of a hill, with cool, winds coming up the slope out
of the bush, semi-shade and very free draining with irrigation at
hand. I hope they succeed this time.
Another plant some have
difficulty with is Pachystegia insignis, or Marlborough
rock daisy. If you find the right position, then there is no problem,
they thrive in the rock garden, clinging to rocks often self seeded,
or planted in rock crevices. If you observe where they are growing
on the Kaikoura coastline they are mostly confined to extremely
rocky positions, full sun, very windy with lots of sea air. We have
found that giving them a side dressing of dolomite lime every second
year seems to keep them happy.
Many of the daisy family
plants can present problems. We have found that they are all very
susceptible to phytophthora. If the plants get stressed at any time
during the summer and autumn then we will lose them. It seems to
be important to keep them well watered so the plants don't go through
a spell of being dry- wet-dry again. The root systems die back and
are very prone to fungal attack. In the case of some, it is not
worth trying. Despite Olearia colensoi, leatherwood being
a major curse when tramping, it has to be one of the hardest plants
to keep alive in Wellington. I've trampled over and under my fair
share of this plant and I am always amazed at how tough it is in
the subalpine belt. It always seems to be constantly wet under foot
and puts up with a range of conditions. We are now trying some plants
in the subalpine area of the new alpine garden; we have placed them
in the shade, in cool rock crevices. It will be a good test of the
soil type we have given them.
The new alpine garden
has four different types of soil. We have stayed away from any bark
component and grown all the plants for the garden in 70% grit and
30% loam (clay and peat). We have gone for this type of mix to keep
the growth of the plants slow, with good drainage whilst having
a good moisture content. If you read in the books about alpines,
they often mention, "enjoys a cool soil, ample water but good
drainage". The challenge is to keep the plants moist but not
wet. The main requirement for our garden was to face south with
good light levels and plenty of rocks to place plants against. Looking
at the plants in the wild they are often on the cool shady slopes,
or if they are in the sun then their roots will be in under rocks
keeping cool, under rock overhangs or nestled at the base of tussocks.
This is what we have tried to achieve.
Another point to be observed
in the wild, is they don't have the "tidy gardener" coming along
and pulling off leaves. Cockayne many years ago pointed out that
"...wild plants will sit in a decaying mass of leaves". What
happens when you do pull off the untidy dead leaves at the base
of aciphyllas, celmisias, anisotomes, astelias, just to mention
a few is you expose the stem or base of these plants to drying winds
and sunlight. It is just about instant death to some celmisias and
aciphyllas if this happens.
At Otari we tend to use
chipped mulch in all our borders. We have found that most of the
plants respond well to the extra food and moisture retention. It
also reduces our weeding time considerably. But that aside, the
hebes benefit well with the mulch layer except for the whipcords.
We have tried a grouping of whipcords with bark mulch around them
and the soil has been too rich, plus the base of the stems are being
buried. The end result has been them browning off. We are next going
to try our alpine soil, and use rock mulch around their bases. Hebes
in general though will benefit from being placed in a windy position,
and mulched around. By doing this with the Hebe cultivar border
we have reduced the downy mildew and leaf spotting considerably.
Last year we moved all
the flax cultivar's to a warmer border and transferred all the new
Marlborough plants to a hot dry bank. Many people were a little
concerned when they saw the flax's shift as we moved them in November
in the warmth. We had found that shifting flax's in the more traditional
time of autumn made them sulk for months. It was also suggested
that we give the flaxes a weak solution of nitrogen fertiliser weekly
and keep them well watered. This has been extremely successful,
Rose Walker, the collection supervisor for the collection may say
too successful as she is back to trimming them regularly.
The Marlborough plants
will do better than their previous home, as they are now on a very
hot, dry north-facing bank. Some of the transplants such as Carmichaelia
spp. and olearias that I thought might not take have grown very
well.
Our next challenge is
to see the new alpine garden growing well and to get some of the
Sub-Antarctic plants going from this years collecting trip, I can
already see Bulbinella rossii and some stilbocarpas., but
how will we replicate constant mist and cold windy conditions. Perhaps
the wind won't be a problem in Wellington's climate.
But for all the challenges
of growing native plants, it is hard to beat viewing them in the
wild in their natural associations, be it the giant kauri's in Waipoua
Forest or an alpine herbfield with mountain daisies in full bloom.
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