Soft cane or Nobile type Dendrobiums must surely be the easiest of all exotic orchids to grow and flower and the range of colours available is unsurpassed by any other type or Genus of Orchid.
Early attempts by some growers were somewhat disappointing with plants making aerial growths (Keiki's) instead of flowers.
These notes are intended to help those people to overcome that problem and to encourage new growers to try them. There are no special conditions needed, just an understanding of their basic requirements.
We believe that by far the most important aspect of their culture is that they have a definite and set time to grow and an equally set time not to grow. When this is properly understood, the rest is relatively simple.
The species from which our modern hybrids are derived were mainly from an area in the lower Himalayas and associated hills in India and the western side of the mountain ranges which run down the Malay peninsula and usually at an altitude of 3,000 to 4,000 feet (900-1200m). In these locations they are subjected to extremes of heat, cold and heavy rainfall, so don't pamper them.
Summer temperatures of 40 deg. and winter down to 0 deg. (canes must not be allowed to freeze) are tolerated equally well if other conditions are looked after.
The time to start to look for good flowers, is when the old flowers are still on the plant. In other words you need to grow a good lead during the summer to be able to get good flowers from it next spring. While still flowering or shortly afterwards, the new leads will emerge and start to grow. As soon as they start to show signs of wanting to grow and not just sit there (usually when it is 3-4 inches long) that is the time to start your feeding program.
Fertilise according to the rate of growth of the new leads, as the growth rate accelerates, so increase the fertiliser rate. As a guide, we start fertilising on the 1st week of November and gradually increase frequency from once per week to twice weekly by about Christmas, then maintain that rate till the end of February or early March, when we stop completely. No more is given to the plant until next season, by that time the new lead has reached its maximum height and only has to fill out the top 2 or 3 nodes to finish its growth. The fertiliser that has produced the best results for us is Peters Blossom Booster at full strength, 2gms per litre.
All Dendrobiums have the capacity to produce new growths from their nodes (Keiki?s). This is one of nature's ways of ensuring the survival of the species. A plant will use this method of reproduction if placed under stress such as when the root system has been damaged or rotted, or when conditions are not ideal. I have seen two collections destroyed by using them to provide extra shade for Cattleyas etc, during summer under fibreglass roof, (conditions were too hot and too dry). All canes shrivelled and Keiki's developed all over them. Using any fertiliser containing Nitrogen on the plant when they are not in active growth will also produce the same results as will trying to grow them under too much shade.
We grow all our Dendrobiums in shade-houses of 30% or 50% shade, even our small plants, although these could be grown under 70% alright. It is important to provide plenty of light for flowering size plants, especially in the winter months. In fact, from about the end of April they should be left in full sun until the buds appear, but remember that the higher the light level the more attention needs to be given to watering in hot weather. Plenty of air movement around the plants helps to reduce the temperature of the leaf surfaces and prevents burning.
During the summer, which corresponds with the wet season in the region where the plants originated, plants require copious amounts of water and as high a humidity as it is possible to provide. After the growth has finished in the early autumn, watering can be tapered off so that by July it should be only necessary to water at 5 to 7 day intervals if weather is dry, increasing again as flowers start to develop.
Size of pots, type of potting material and water frequency are all inter-related. In brief, the smaller the pot and the more open the mix the more often the watering will be needed. However don't use larger pots or finer mixes than necessary. We grow our single flowering cane plants in 100mm (4") pots and a mix of 2/3 casurina bark (1/4 to 1/2" grade) and 1/3 pearlite and water well in the late afternoon daily during summer. On hot days (over 30deg C.) we give a 4-5 minute watering once or twice during the day, mainly to increase humidity.
Repotting is best done as soon after flowering as possible and before the roots on new leads can be damaged. If any organic material is used in the mix, such as bark etc. its limit will be about 2 years.
When dividing or trimming old growths at re-potting time we leave 3 years growth on the plants. Those old canes act as a reservoir for food for the new growths.
Pests & Diseases
These orchids are subject to attack by pests that growers know only too well and are treated with insecticides appropriate to the pest. The exception to that is leaf spotting. A fungus causes this and we control it completely by spraying every week. Either DITHANE 45 or DACONIL 2787 should be satisfactory.
Soft cane Dendrobiums need a cooling off to initiate flower buds, Yamamoto say a month of nights at about 10 deg. C is needed, but we believe that 13 deg C is cool enough.
If plants are placed in a position where good light reaches the full length of the flowering cane at bud initiation time, you will find that they develop over a greater length. If crowded together, at that time, flowering will be confined to the top sections.
Some helpful hints: A porous floor covering that can be kept wet, sawdust or woodchips are good or some sort of plant growing on the floor will improve humidity. The closer your softcanes are grown to the floor the better. Hanging plants to the roof provides the lowest humidity. Polystyrene boxes turned upside down, with holes in them to the pot size are good to hold plants upright and trap moisture in the root area,a definite plus.
It will also help if plants are grown fairly close together for the hot growing season, but space wider in autumn for better flowering.
Flowers are long lasting but keeping the plants cool can extend this and the flowers dry when watering.
TO SUM UP
1. Fertilize and water freely all summer.
2. Stop fertilizing not later than mid march.
3. Water all year if conditions are dry.
4. Grow under plenty of light and air movement.
5. Sit back and enjoy the results.
Keiki's: Make sure these are well developed before you remove them, (too early and there is a long period of stagnation). Do not plant them too deep or new growths will be buried. Old canes can be cut into 75mm segments or left whole and laid on moist sphagnum or vermiculite. These will throw growths in 3-4 months.
For the leaf eating caterpillars and loopers, which can shred leaves in a couple of days, use carbaryl.
Some clones flower more easily than do others. Go to shows, write down the varieties that take your eye, and remember, purchase good strong healthy plants.
Cleanliness: Your potting bench should be kept clean. Under benches should be kept weed free and it is important that dead and yellowing foliage should be collected on a regular basis.
Note: Both Carbaryl & Mavrik (Pyrethin) are natural occuring substances and can be used with little damage to the environment when used as directed. Also Daconil is recomended for Glomerella in Cymbidiums, so if you have to spray the Cymbidiums then wave it over the Softcanes as well.