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Short Cuts in this issue:
- Growing Australian Dendrobiums
- Uncomplicated advice for growing some Australian orchid "gems"
- Vegetative Propagation of Eucalypts
- There are alternatives to seed - but there is still much to learn
- Cuttings in the Cold
- Don't hibernate in winter; there's cuttings to be had!
- Australian Plants and the Senses
- Smelling, touching, feeling and hearing....a recipe for total enjoyment!
- Botanical Terminology - The Flower
- There's no need to be confused by those obscure botanical terms - we explain all!
- Preventing Disease in Potting Media
- It's not just the large commercial nurseries who should be concered about hygene.
Growing Australian Dendrobiums
Orchids often have an intimidating "mystique" for the beginner but David Banks outlines basic procedures for growing some top class Australian species and hybrids
The following comments on growing Australian Dendrobium orchids refer to the cool growing species and hybrids within the Dendrocoryne section. These species and their hybrids will grow happily in the bush house in frost-free areas. Most of the hybrids around have the species D.kingianum, D.speciosum and D.tetragonum in their background. These plants are vigorous and pass this trait onto their progeny. Hybrids with D.tetragonum var.giganreum and D.fleckeri have the ability to flower throughout the year at varied intervals. If a grower chooses plants correctly, it would be possible to have native Dendrobium hybrids in ffower for at least eight months of the year.
We grow all of our native orchids under 50% shade. These include seedlings and mature plants. The benches are 60 cm above the ground and are wooden. All our pots, up to 150 mm pot size, are plastic, preferabIy squat. After 150 mm pot size we move into squat terracotta pots. The most important factor to consider regarding the cultivation of any orchid is drainage and air movement.
Dendrobium "Bardo Rose" is a hybrid between D.kingianum and D.falcorostrum. It is easily grown and very colourful. Select the thumbnail image or plant name for a higher resolution image (23k).
Watering for Dendrobiums
Plants are watered between once and twice a week during the cooler months, whilst in the warmer months plants may be watered once a day due to the good drainage of our mixture. In the
warmer months, we water just on sunset, while early in the morning is the rule in the cooler months.
We don't use any fungicides, as these tend to weaken the plant in my opinion, and then make it vulnerable to disease. We fertilize our plants with Nitrosol, Aquasol, Maxi-crop or an organic fertilizer at half strength during the growing season (spring to early autumn). The growing season varies with every different clone.
Native dendrobiums have few pests, the maln ones being caterplllars, which are a problem when the new growths are young and when flower spikes are present. Other pests include scale, mealy bug, aphids and snails. Normal precautions should be taken to prevent these.
Plants can be re-potted from mid-spring to mid-summer, thus giving the plant the chance to re-establish before winter.
Our compost consists of a mixture of 50% pine bark (small grade) and 50% gravel (pea size). This allows for perfect drainage. Charcoal is not used as it tends to be a blotter for salts, and whilst charcoal may be good for the first six months, it tends to go sour, leading to root rot. I often wonder wl·ly people use charcoal in their mixes, as it is unnatural. How often do you see plants in the wild growing in or on charcoal? In the wild, D.kingianum commonly grows on conglomerate, a sedimentary rock made from compressed pebbles which are cemented together. The roots run along the pebbles which gives the roots a cooIing effect. Sandstone is not used as it also tends to be a blotter for salts and water.
Gravel (river pebbles) is used for the following reasons.
Pine bark is used as it is fairly readily available. However, she-oak (Casuarina torulosa) bark would be preferable, but it is hard for us 'city-folk' to get, as you have to collect it yourself.
- It doesn't absorb salts
- It is cheaper than charcoal
- It is re-usable as it doesn't break downl
- It improves drainage
- It adds weight to pots -- plants don't blow over easily
- It doesn't hold water - this can't rot roots.
A number of plants produce aerial growths, which can be taken off when mature. These are cornmon on the species D.kingianum and D.fleckeri, and the hybrids D.delicatum, D."Bardo Rose", D."Ellen" and D."Hastings". Note that these hybrids are progeny from D.kingianum. These aerials can be taken off and
placed in 50 mm tubes with an inch of sphagnum moss in the botlom. Roots form within a few weeks and then you will have a new plant to add to your collection.
Aerial growths from a plant of Dendrobium x delicatum can quickly produce new plants. Select the thumbnail image or plant name for a higher resolution image (13k).
Given a bit of attention, and the careful selection of your planls, your bush-house should be a blaze of. colour in springtime when these native gems are in flower. The colours available range from whites through pinks to deep purples and creams through yellows to apricot. Native Dendrobium species and hybrids are worth a place in every orchid collection.
From the June 1983 issue of "Native Plants for New South Wales", newsletter of the NSW Region of SGAP.[ Return to Index ]
Vegetative Propagation of Eucalypts
Vegetative methods of growing eucalypts have not been generally successful but, in some cases, promising results have been obtained.
By far the most common method of propagating eucalypts is from seed. This is for a good reason. Eucalypt seeds are readily available, and very easy to germinate under a wide range of conditions.
But what about vegetative propagation? Well, it certainly is desirable where you wish to preserve a particular strain or form. The most serious problem preventing the more widespread use of vegetative propagation of eucalypts is the fact that cuttings from adult trees do not form roots. Therefore, by the time a tree has shown its potential for characters such as growth rate, insect and disease resistance, unusual flower colour, it cannot readily be propagated by vegetative means. However, vegetative propagation of eucalypts is possible under certain circumstances. There are instances of vegetative propagation under natural conditions ie. rhizomes formed by some tropical species, and separation of large lignotubers to form individual new plants in some other species.
Vegetative methods are the only way that propagation of unusual coloured forms of eucalypts, such as this pink form of the usually white Eucalyptus sideroxylon, can be guaranteed. Propagation from seed may or may not give the desired result. Select the thumbnail image or plant name for a higher resolution image (33k).
Artificially, vegetative propagation can be attained in a number of ways.
1. Stem Cuttings
Cuttings taken from young eucalpyt seedlings readily form roots. However, only young seedlings, less than a few months old, will respond in this way. Therefore, the advantage is not great, as relatively few cuttings may be obtained from any one seedling. Eucalyptus polybractea, a species having a high concentration of essential oils in the leaves, has been vegetatively propagated from seedling cuttings, so the potential exists for the building up of high-oil forms. In all species examined, the rooted cuttings grow as vigorously as seedlings. E.deglupta is exceptional in that roots form readily on cuttings taken from plants up to a year old.
2. Epicormic Shoots
Epicormic shoots (coppice growth) develop in most eucalypt species following felling or girdling, and after damage due to fire or insect grazing. Stem cuttings taken from vigorously growing epicormic shoots near the base of a tree retain the ability to form roots. This is a useful method of propagation as many eucalypt species have the ability to produce very large numbers of basal epicormic shoots. However, the use of basal epicormic shoots as cuttings does not provide a universal method of propagating adult eucalypts vegetatively, as several important forest species do not coppice readily: E.regnans, E.delegatensis, E.fraxinoides, E.nitens, and E.astingens. Seasonal effects are important in the rooting of cuttings derived from coppice shoots, even in equatorial climates. These seasonal effects, obviously not due entirely to temperature changes, have been little studied, and there is plenty of room for experiment.
Most eucalpyt species develop lignotubers (woody swelling at or around ground level) which contain numerous buds and meristematic tissue. Lignotubers may form shoots after the trees have been damaged by fire or insect damage. These shoots may often be used successfully as cutting material. Also, pieces of lignotuber tissue have been used to propagate 2 year old seedlings of E.tereticornis, after the lignotuber was treated with lndole Butyric Acid (IBA) and planted in pots at soil level.
Air layers can be applied to young trees or to the basal epicormic shoots of adult trees. As with cuttings, the rooting of air layers is affected by season. About twenty eucalypt species have been successfully layered so far.
Grafting is a method of propagating difficult species, or is used to exploit certain characteristics. It is however, a labour intensive operation, and so its use is limited by cost. The most useful grafting method for eucalypts has proved to be Approach Grafting. Delayed graft incompatability is a problem. The establishment of a graft union is not necessarily related to the future growth and compatibility of the graft.
In ornamental horticulture, a particularly desirable species or form is grafted onto a related but hardier species eg. Corymbia ficifolia can be grafted onto C.gummifera; Eucalyptus phoenicea can be grafted onto E.baileyana rootstocks.
[Further details of grafting methods can be found at the Society's
Plant Propagation pages.]
6. Tissue and Organ Culture
Tissue and organ culture techniques are now often used in preference to other methods of propagating trees vegetatively because of the very high multiplication rates that are possible (usually millions per year). Eucalypts have been succesesfully propagated using these methods, but the best growing media and plant parts to use, are still under investigation.
From the July 1985 issue of the newsletter of SGAP's Eucalyptus Study Group.[ Return to Index ]
Cuttings in the Cold
....or put another way "Now is the winter of our discontent", to quote from one Will Shakespeare.
Ross Doig has some thoughts on helping cuttings survive the winter chill.
Is it worth holding cuttings during winter (June to September in Australia) when growth is minimal?"
In an ideal world where plant material is available at call the answer is a resounding NO.
But plant enthusiasts tend to most active in winter months - visiting gardens, excursions near and far within their own State and Interstate, discovering cutting material at florists, and in many instances experiencing one-off chances to collect cuttings.
Besides, in much of Southern Australia with its Mediterranean climate, winter rains encourage new growth over a wide range of species. Even in New South Wales and further north where semi-dormancy exists, new growth is usually present if searched for. Be assured, in the protected environment of the cold frame, igloo bush or shadehouse (devoid of misting or bottom heat), cuttings will survive low temperatures without harm. In fact, in most places winter sunshine will enable many herbaceous species in particular, to readily take root.
Which causes me to pose the rhetorical question. So what is the problem?...and to answer immediately - most of the damned things just sit there, some rot, a few are subject to mildew and fungal attacks, but from early spring onwards the majority begin to strike.
And there are even some advantages at this time.
So to conclude. Don’t close your system down, bear with the slow down in strike rate and take advantage of the other positive factors which make winter propagation a viable concern.
- Watering - kept to a minimum and provided light and air get to the cuttings (to avoid rotting problems), once a fortnight is possible (time for that holiday!)
- Warmth- the more sun the better for all systems. It is here that a portable covered box is most useful. At this time most herbaceous cuttings strike.
- Mediums- for plants susceptible to rot, an open gravely mix seems best. For others, more coco-peat (environmentally desirable over peat-moss) will allow shorter tip cuttings to be used
without fear of drying out too rapidly.
- Types of cuttings - for Proteaceae, Fabaceae and Asteraceae species, longer cuttings (up to 30cm) and often with several terminal shoots, may be taken. Conversely smaller (up to 30cm) cuttings of younger wood often hold better than in the hot summer period. With both types, at least double the number of leaves usually retained in the summer can be left on cuttings and seems even to stimulate rooting in some cases.
From the July 1996 issue of "Blandfordia", the newsletter of the Society's North Shore District Group.[ Return to Index ]
Australian Plants and the Senses
Beauty is not limited to the sense of sight. Dr Gordon Myall looks at the ways that the senses of touch, smell and hearing can combine for total enjoyment of our natural surroundings.
We interpret the world through our senses. Our perception of the world arrives through our senses. Each of us may see it in a different way, defining our environment in terms of pleasure, beauty, enjoyment though sometimes with anger.
From the point of view of technical botany, there is a limitation, in that we dcscribe plants mainly in visual terms. Technical language cannot define smell and touch. We always compare them with something with which we are familiar.
All senses are the result of stimulation of receptors, which are joined to nerves and which
follow well defined paths to the brain. Here they are computed, modified and joined to other
sensory perceptions and then reach consciousness.
Timing is another factor. Some of the pathways are rapid. e.g, a pain sensation may travel up to 100 m/sec, whereas smell travels at about 0.5 m/sec. The speed of nerve transmission is for safety. If you suffer a sting from a stinging tree, you withdraw before too much damage is done.
Hearing is not often considered in botanical terms but plants do have sounds. The wind blowing
through casuarinas or the bursting of pea pods indicate that the silence of the bush is not really
Smell is a sense that we are very much aware of when we are in the bush. Some odours are
pleasant, others may be quite the reverse. Technically smell and taste are the same. e.g. the taste and smell of lemon-scented tea tree are identical. Classically there are three modalities of taste; sweet. bitter and salty. Not everyone is able to detect or interpret the same smell in the
same way. The wonderful perfume of Boronia megastigma is only enjoyed by 75% of the population.
The mint bushes (Prostanthera sp) are well known for their strongly aromatic foliage and are often planted alongside paths so that this feature can be appreciated. This is the pink form of the normally purple Prostanthera rotundifolia.. Select the thumbnail image or plant name for a higher resolution image (21k).
A number of Australian plants are used to make pleasant tasting herbal teas. Backhousia citriodora, and B.anisata are used commercially for this purpose. Select the thumbnail image or plant name for a higher resolution image (37k).
Vision is the sense of which we are the most aware. The eyes are designed to see the world in three dimensions. We can judge distance because we have two eyes, Try closing one eye and touch a single point - it can only be done with practice. We judge colour in a rather irregular fashion, with different definitions and different names. It is interesting to note that few botanists give colour in their plant descriptions because it is very much a question of a
particular person's perception of colour.
As lovers of the bush, we should be aware that we are in a total environment in which every sense should come into play, from the overall to the particular from the opening of a leaf bud to the stand of timber on a distant hill. We should be aware of the perfume of a stand of acacias, the smell of new mown hay or even 'dynamic lifter'. We should listen to the wind, the sound of bees, even the smell of hops when we arrive home tired and happy!'
From a talk by Dr Myall to the Coffs Harbour District Group of SGAP on 4 December 1996.[ Return to Index ]
"Dynamic Lifter" is a brand of organic fertilizer made from poultery manure!
Botanical Terminology - The Flower
Confused by carpels? Angry about anthers? Or just flumoxxed by filaments? Bob Wilson explains why it's all quite simple really....provided you have a powerful magnifying glass.
The main parts of a flower are shown in the accompanying generalised diagram and are defined as follows.
Anther: The pollen bearing part of the stamen.
Carpel: The female part of the flower consisting of the ovary, stigma and interconnecting style.
Filament: The stalk of the stamen.
Ovary: The base part of the carpel containg the ovules which develop into seed after fertilisation.
Petal: A leaf-like part, often highly coloured, which protects the reproductive parts of the flower.
Receptacle: The end of the stalk, often expanded, on which the flower arises.
Sepal: An outer leaf-like part of the calyx surrounding the petals.
Stamen: The male part of the flower consisting of anther and filament.
Stigma: The part of the style which receives pollen. It is usually sticky and on the end of the style.
Style: The stalk joining the stigma and ovary.
Other terms used but not shown in the diagram are:
Androecium: Collective name for stamens.
Gynoecium: Collective name for carpels.
Calyx: Collective name for sepals.
Bract: Modified leaf associated with a flower.
Bracteole: Bract attached to either flower stalk or calyx.
From the July/August 1996 issue of the newsletter of SPAP's Newcastle District Group.[ Return to Index ]
Preventing Disease in Potting Media
A lot of effort goes into propagating plants so it makes sense to give them the best chance of survival. Kevin Handreck explains some of the things that can be done by even the home gardener.
It is important first to understand one concept about the micro-life in soils and other growing media: most of the micro-organisms in these media are beneficial to plants. Plants benefit through the release by micro-organisms of nutrients locked away in organic and mineral materials around roots, through symbiotic associations (eg.' rhizobium bacteria and legume roots, mycorrhizal fungi, actinomycetes and casuarina roots), and through biological control of disease-causing organisms.
A sterile medium is one in which all of the life in it has been killed. Clearly this is not a desirable situation. At the very least, we have no rhizobium bacteria, mycorrhizal fungi, or actinomycetes. At the worst we have a vacuum, and we all know that nature abhors a vacuum. It tends to be filled by the first micro-organisms which come along. If they happen to be pathogens, then they will grow unchecked, with disastrous consequences for any plants we place in the medium. Sterilization is accomplished through the use of such nasty chemicals as methyl bromide or by raising the temperature of the medium to at least 100 degrees C.
There are several ways by which the pathogens in growing media can be reduced in numbers while still retaining beneficial organisms. The best one is to start with uncontaminated materials. More about this later. Another is to suppress the activity of the pathogens through the use of chemicals. I use the word 'suppress' rather than 'kill' because many of the chemicals used to control root diseases do not give a total kill; they reduce numbers or reduce the activity of the population, so damage to plants is reduced. Of course one almost inevitable outcome of the repeated use of a particular chemical is that the pathogen evolves to produce a population which is resistant to the action of the chemical.
Yet another method of selectively reducing populations of pathogens is through the controlled use of heat. The temperature of the moist medium is raised into the range 60-80 C and held there for about 30 minutes. Most pathogens are more sensitive to heat than are their antagonists, so they are selectively killed. Unfortunately, most rhizobium bacteria and mycorrhizal fungi are also killed, but at least the large population of other micro-organisms remains largely intact. The term pasteurisation has been used to describe this process of selective killing. Pasteurisation may be accomplished by passing aerated steam through the medium, or by heating it in an oven or, by the sun.
Pasteurisation is not easy to achieve with a domestic oven as the temperature is too low for accurate control in most of them. It is easier with a microwave oven. A convenient method is to transfer the moist medium into 4 litre icecream containers. Place one of these in the oven and heat it for 6 minutes at full power. Transfer to an insulated container such as an Esky or similar, so that it remains hot for at least 30 minutes. Cool briefly and use, or cover for later use.
Solarization is a form of pasteurisation in which the sun provides the heat. The moist medium is placed in a layer no more than 10 cm thick on a solid surface - concrete or asphalt - and covered with thin, clear plastic sheeting. This sheeting must be sealed to the solid surface so that air movement under it and into the mix is eliminated, or at least reduced to an absolute minimum. The sun must be able to shine on the medium for most of the day. Provided that the air temperature is at least 25 C and there is little interference from clouds, the medium should be pasteurised in a day or two. Clearly solarization can only be done in the summer.
|"In my view, any natural soil to be used in a potting mix should be pasteurised to ensure freedom from pathogens."|
Those commercial nurseries which pasteurise their growing media do so with aerated steam, or they use a flame to heat the mix which is tumbled through the flame in a carefully controlled way.
It is legitimate to ask whether it is really necessary to pasteurise growing media to be used in containers. Many nurseries have concluded that it is not necessary for the soil-less potting mixes which they now mostly use for growing on after propagation. However many do pasteurise their propagation media. Many bedding plant nurseries pasteurise. By including some recycled 'dump' mix (mainly from unsold punnets) in the new mix they ensure that it has a high population of beneficial micro-organisms. Most such nurseries find that they do not need to use any chemicals to control root diseases as they have none.
Other nurseries use composted bark as the main component of their propagation medium. A compost heap typically stays at 50 C+ for many days to several weeks, so pathogens in it are killed.
I now come to the relevance of this to those enthusiastic growers who raise plants for either their own use or for sale or giving away. What is the best way of avoiding disease during production, and the spreading of disease via your plants? Methyl bromide is out. Aerated steam is impossible. Chemicals are not a sensible answer. Solarization can be used only for a limited part of the year.
My suggestion is to follow the example of commercial growers:
By following these few simple guidelines, root disease should rarely be a problem for growers of Australian plants.
- Media for propagation by cuttings or by seedlings which are to be picked out into larger containers should be either pasteurised in a microwave oven or by solarization, or be composed of materials such as perlite and vermiculite which are likely to be free from pathogens. Wherever possible, the cuttings themselves should be taken from parts of plants which are above the reach of soil splash. It is usually desirable to soak the cuttings in dilute bleach solution (about 50ml per litre of water) for 10-20 minutes to reduce the population of bugs on their surfaces.
- General potting media composed of such materials as aged or composted pine bark, composted sawdust, peat, and washed sand, can usually be assumed to not need treatment. Most nursery stock, including that of large native plant nurseries, is now grown in such media without any treatment, and with little need for chemicals.
- In my view, any natural soil to be used in a potting mix should be pasteurised to ensure freedom from pathogens.
- Having started with a clean mix, it is essential that it be kept clean. Pots or tubes should be placed on gravel or weedmat so that soil cannot be splashed into them. Hygiene should be excellent at all times.
From the February 1988 issue of the newsletter of the South Australian Region of SGAP.[ Return to Index ]
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Australian Plants online - June 1997
The Society for Growing Australian Plants