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Growing Dendrobium section Rhizobium

Growing Dendrobiumsection Rhizobium

Once a seed pod is formed, the seed is sown, the seed germinates, the mother flask is replated, the seedlings are removed from the flask, and the seedlings are potted up, it is time to decide how to grow this seedling into a mature plant.

Over our years of growing Dendrobiumsection Rhizobium we have experimented with many different pots, medias and environmental conditions.

Many growers have used gutter guard poles, pots cut in half and then joined back together with a strip of gutter guard, recycled rubber coir, mesh pots, hardwood, cork, and tree fern. However, we have found a quality ‘squat pots’ achieves the best results in our conditions.

In saying that many Victorian growers have equal successes by growing Dendrobiumsection Rhizobium species and hybrids on large cork mounts with a small amount of bush or sphagnum moss. While in Queensland it seems mesh pots are still favourable. We believe the plants drying out very quickly to be the reason mesh pots and mounts were not always successful.


We prefer to use various sizes of ‘squat pots’ manufactured by the Orchid Pot co. These quality pots come in an extensive range of sizes and are made of durable plastic. The free draining design is the reason these pots have been so successful.

Growing Media

We recommend starting with a quality treated Kiwi Pine Bark, Size 2 for 50mm-80mm pots and Size 3 for anything above. Pine bark makes up around 70% of the media, the remaining 30% is 10mm scoria rock. A mixture of chopped sphagnum moss and perlite may also be useful in growing cuttings with minimal or no root growth.


Avoid high Nitrogen fertiliser; it leads to soft, fungi prone growth and few flowers. We use a high Potassium fertiliser with a N: P: K of 8:5:25, at a rate of one gram per litre of water fortnightly, all year round. We compliment this by using Amino Grow, as a drench or foliar feed, this helps the uptake of Potassium (k) whilst also maintaining a high level of sugars. To maintain optimum results, we use micro-fine lime the rate of one gram per litre, we do this in early autumn and again at the beginning of spring.


We recommend the well know organic ‘horticultural oil’ recipe;

2 cups of vegetable oil + ½ cup of dishwashing detergent. Shake together in a jar, where the mixture will turn a milky colour. Add 2 tablespoons of this concentrate to a litre of water and it's ready to spray. This controls most insect pests, including scale, aphids, white fly, leaf miner, mealy bug and mites.


The following four organic recipes are listed in order of strength;

Bicarb spray - Two teaspoonfuls bicarbonate of soda, half a teaspoonful of sunflower oil and a drop of biodegradable dishwashing liquid to one litre of water

Powdered sulphur, dusting grade - Simply dust over plants, but not when the temperatures exceed 30 degrees Celsius

Lime sulphur spray - One tablespoon of lime sulphur to one litre of water

Bordeaux spray - Add 100 grams of builders', brickies' or hydrated lime to half a standard plastic bucket of water, stir well. Add 100 grams of copper sulphate to a separate plastic half-bucket of water and stir until dissolved. Then pour the lime water into the copper sulphate water and mix thoroughly

House Coverings, Watering, Air movement and Humidity

Our main tunnel house is covered in 30% black shade cloth. This allows maximum light which most species and hybrids of this section require to produce masses of flowers. However, some species such as D. pugioniformemay prefer slightly less light. Species such as D. chordiformisand D. erythraeummay grow better with a covered roof over the winter months. These plants, in our conditions prefer to remain consistently moist all year around. No ‘dry spell’ is required for most species and hybrids, apart from D. teretifolium var. calamiforme which will benefit from reduced watering in the winter. Constant and consistent air movement is crucial to growing this section. We have found that hanging the plants helps in achieving this. In regards to humidity, while not necessary I believe it aids in keeping these plants consistently moist thought the warmer months.

Mount culture

We are not the biggest fans of mount culture, and most of our collection of around 1000 mature plants have been growing in pots for some years. However, some species require mounts to flourish. These are, the D. teretifoilumcomplex,D. cucumerinum,D. linguiforme,D. pugioniforme, D. racemosumand D. rigidum.The listed species have all grown well on cork mounts or aged hardwood.


Add a little water to the Flask if the agar is slightly hardened, swish around and your new seedlings should slide out. Rinse the seedlings in water and be sure to remove all agar mixture from the roots. Then place them in a solution of Envy and soak for 5 minutes, lay them on damp newspaper overnight, then pot your new seedlings up the next morning. Do not let these new seedlings dry out, keep them protected from extreme weather and if any signs of fungi appear use a fungicide at a low rate. Avoid large community pots as a fungal infection may wipe the entire pot out.

Propagation and Pruning

This section can be propagated quite easily. It is best to take a cutting when a new aerial root (outside of the pot) forms. Simply cut above this new root when it is 5cms long and pot into a 50mm tube. If a cutting has no roots a rooting hormone may be useful. The pruning method is used to initiate new growths at the base of the plant. Older plants, especially those with the D. teretifoliumcomplex or D. schoeninumespecially may need pruning. These plants sometimes become full of ‘dead wood’, growths are lengthy and don’t flower. We suggest pruning after flowering and before new growth initiates. Be careful not to prune to hard. We usually take 2-5 growths off.

Whichever way you choose to grow Dendrobium’s from this section, I am confident their hardiness and the large floral displays that mature plants produce will be rewarding and inspiring.

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