Notes about tuberous orchids (long)...

John Taylor [Catweasel] (
Fri, 28 Oct 94 12:53:31 DST

I've been reading up on growing our native tuberous orchids, and I think some
if not all of the methods used may be applicable to tuberous Drosera...

The following are extracts from "Cultivation of Australian Native Orchids"
(2nd Edition) produced by The Australasian Native Orchid Society Victorian
Group Inc. I'll stick with the "Storage of dormant tuberoids" and the major
parts on watering... (I may post other parts later if I think they're
suitably applicably for tuberous Drosera...)

Tuberiods can be successfully stored for several months provided they
are kept dry and prevented from dehydrating. It does not matter if they shoot
and start to grow, although the sooner they are potted up then, the longer and
therefore better will be their growing season. Suitable dry materials in which
to store tuberoids are dry sand, dry potting mix or dry tissue. Some types of
peat moss may damage tuberoids, so it is best avoided. The dry materials
around the tuberoids protects them from knocks and adsorbs any moisture which
might be produced from sweating.

To prevent dehydration, tuberoids should be stored in the dry material
in a sealed plastic bag. Paper envelopes are not suitable because they are
porous and dehydration of tuberoids will occur if they are left for several
weeks, especially if the weather is hot.

If the tuberoids are stored, packed as suggested above, in a cool, dry
place, for example, a cupboard, they will remain in a satisfactory condition
for three or four months. Slight shrivellingmight occur, but that does not
prevent regrowth."

When a terrestrial orchid is growing, it needs a constant supply of
water and nutrients. The mix must therefore be moist through the growing
season. This means that plants grown under a solid roof will need to be
watered regularly and plants grown under shade cloth or in the open will
sometimes need supplementary watering.

The techniques of watering is to fill pots to the top of the rim with
water. A hose fitting which gives a gentle spray (eg. rose fitting) is best
as it will not damage plants or disturb the top of the mix. The 10mm gap
between the top of the mulch and the rim of the pot holds the water which
quickly flows down through the mix, thoroughly wetting its entire contents,
the excess draining away through the drainage holes. If the mix is draining
properly, there should be no water remaining on top of mix after about 10
seconds. Do not leave a saucer under a pot as this prevents excess water from
draining away and keeps the mix at the base of the pot too wet.

After draining, the pot is holding its full capacity of water for that
mix. Over time it will be used by the plants and evaporate from the surface
of the mix until there is insufficient water in the pores of the mix for the
needs of the plants. This loss varies with temperature and air movement.
Terra-cotta pots also lose water from all around the pot because they are
porous." (Terra-cotta pots are not recommended...) "The frequency with which
your pots need to be watered therefore varies according to your conditions,
ie. temperature and air movement around pots, size and type of pot and the
openness of your mix.

How do you decide? Lift mulch and feel the top few mm of the mix. If
it is dry, thepot needs watering. The moisture level of the pot can also be
checked by having a spare pot with mix only in it which is watered with other
plants. Tip this pot upside down with hand held over mix and gently remove
the pot. The mix should hold together and allow you to observe the moisture
level of the mix half way down.

The moisture level of the pot can also be checked by removing the label
and inspecting its base. If it is sticky and damp, there is enough moisture
in the pot. The weight of the pot also varies with the amount of water

Terrestrial orchids vary from many other plants by not initially
wilting from lack of water (as do fuchsias, azaleas and others). The signs of
underwatering are difficult to detect because it is the underground parts of
the plant that are mostly affected. Underwatering, or a mix not properly
wetted can go on undetected all season if you only casually observe plants.
The results are poor growth of plants and fewer, smaller or no replacement
tuberoids being produced. Overwatered plants have growth reduced because of
lack of oxygen at root level. Benificial organisms in the mix also suffer from
lack of oxygen and rotting of plants and tuberoids is likely to occur. Signs
of overwatering are also difficult to observe in the plants until it is too
late and much damage has occured, ie. plants and tuberoids rotting.

There is no hard and fast rule, but you learn to judge when to water
by careful observation of plants and mix,

Average watering frequency:
Warmer months (autumn and spring) every 1 to 2 weeks.
Colder months (winter) every 2 to 4 weeks.

During the dormant period, tuberoids do not use water or need
nutrients, but they must not be dehydrated. In their natural habitat, most
tuberoids are well protected from dehydration and excessive heat, but in a pot
they are not well protected. A light spray of water once a week or so,
depending on conditions, prevents dehydration and cools the pot a little. The
pots must not be thoroughly wet through as in the growing season."

When pots are watered for the first time after being dry over summer,
care must be taken to wet the entire contents thoroughly. The water can run
down the inside of the pot and not through the mix. If necessary, immerse
pots in a bucket of water for an hour or so to wet the contents. Particular
care must be take with mixes containing grey coastal sandy loam as this repels
water when dry and be quite difficult to wet again." (Tell me about it!!)

There are other good sections in this book, including a shadehouse design,
month-by-month growing calendars, average tempature and rainfall for the
capital cities of Australia, life cycles of terrestrials, pests/diseases, etc.
It was certainly worth the AUS $10 I paid for it - I'm not sure if this was a
special price for members or not (it was included on the subscription form for
the ANOS-VG which I'm pretty sure was only $10/year for single or family).

I'll try to experiment growing tuberous sundews in the terrestrial orchid mix
instead of the usually peat/sand. Since both plants grow in the same areas
here I think it may well be very successful. I'll keep you all posted...


| John Taylor [Catweasel] | Royal Melbourne Institute of Technology |
| | Department of Applied Physics |
| | Melbourne, Victoria, AUSTRALIA |