Growing Dendrobium speciosum

Potting mix is the major decision you must come to grips with if you want to grow great speciosums. More words have been written on this topic than what appears in the Australian Tax Office guide to working out your annual Tax Return. You must realise that potting media and your watering regime go hand in hand with the selection of your pot size and shape. These three factors will govern whether or not you will be successful long term. And this may take you a while to work out using trial and error. There are no shortcuts.

It is not particularly hard to learn, so panic is not necessary. If you are a new grower you will need to know a couple of things. If you are strolling through Bunnings or the local supermarket and you see a bag of something labelled ORCHID POTTING MIX, please run for your life. 99 times out of a hundred this mix will be made for exotic Cymbidium Orchids. It is totally inappropriate for use with D. speciosum. You need to look for coarse or medium grade ORCHID BARK. This can be surprisingly hard to locate. Your best bet will always be to find a specialist orchid nursery. Even then, they often sell out and have no stock.

Orchid bark is graded and composted pine bark. Going down to the Landscape Supplies Yard and getting a box trailer full of uncomposted pine bark is not the way to go. Untreated pine bark has harsh toxins and phenols in it that will slow root growth. Some really good Orchid Bark is further treated with chemical additives that get rid of all these unwanted components of the pine bark. To sum up, do not waste your time with anything other then pre-packaged “ORCHID BARK”. But never touch Orchid Mix. Got the picture?

Orchid Bark comes in three sizes usually: Small, Medium and Coarse. What you use depends on a couple of important points. Firstly, the size of the piece you want to pot on. If you have ended up with a leading piece with three or more pseudobulbs as thick as your forearm, then you will be reaching for the coarse grade. That is if you are potting into a large pot. If you are a miser with your bark and pots and try and save a few cents, then you should be using the medium grade. If you end up with a few solid, leafless back bulbs that you think have potential, then you should be whacking them into the small grade, or a mix of small and medium.

Pot size is hard to explain. The big danger is writing about it, instead of demonstrating it to someone, particularly new chums. If you are potting on advanced seedlings into a 100mm or 150mm pot, then a good rule of thumb is to put it into a pot that is only twice as big as the plant in width. But not much deeper then the pot it came out of. And in this example you should be using medium size bark. Definitely not the coarse grade that would have too much air between the bark pieces. Ask a more experienced grower for advice if you know one.

Never stick a plant from a 100mm pot straight into a 250mm pot or bigger. It will just sit there like a half eaten sausage roll on a paper plate at a party. Consequently, it will take an extra few years to start growing along the way it should. Your object is to have your mix stay damp and humid, not to have it stay wet and smelly. And for heavens sake, never sit your pot in a saucer and think what a great grower you are. Wet feet is the greatest mistake you can make with D. speciosum.

Most growers add various things to the bark as they use it. For large clumps in large pots, I am a dinosaur. I cannot convince myself to leave out a good handful of 15-20mm rough crushed rock/gravel. I know I know . . . modern growers shy away from using this rock these days. But I believe it lends rigidity to the mix and this is mighty handy if you are potting up a big piece with tall bulbs. I cannot believe that it does any harm. Big orchids can rock back and fourth and damage tender young root tips. You do not want this to happen. A bit of rock mixed with the bark will certainly make your specimen plants heavier, but sturdier.

Some people mix handfuls of polystyrene into the bark. They either break up old boxes into suitable size bits, or they go to Kmart and buy those big bags of beanbag polystyrene balls. They do have the advantage of staying warmer than rocks in the wintertime and this may aid in the roots staying a bit on the active side. Others use Perlite in their mix. Years ago others used Scoria, a volcanic rock. Some have used glass wool, so I have read in orchid magazines. Holy hell! I have no idea what glass wool even is! I just pass the messages around; I seldom make them up.

I will tell you one thing that you should be aware of. Ten years ago, a whole bunch of growers got caught up in the rush to use chopped up coconut husk as potting medium. This product came here in great bales from the tropical regions and it was cheap and easy to use. I and others issued guarded warnings about its use. We believed that it would inevitably become too wet and cause troubles. I have heard rumours that some growers have had their wings clipped and regret having ever seen the stuff.

Chief among the issues was, surprise surprise, D. speciosum plants started to go backwards. Third hand information was varied. Some ideas were that you had to repot every couple of years or the coconut started to rot, along with the orchid roots. I also heard reports that heavy use of fertiliser and chemicals caused issues. I really do not know the problems first hand. I also hear that some big nurseries have stuck with coconut husk/fibre and have had great success.

In a lot of instances, and with many other species, coconut might be simply brilliant, but I will not believe it for D. speciosum. Perhaps if the watering regime has been worked out whereby the coconut is left til nearly dry, then it may well be possible to maintain the balance of water and air at the correct levels. The first few months of 2012 in Sydney experienced record rainfall. If you had an open bush house, you had no choice in how much water your plants received. I even lost some growths that were left a bit long in the normal bark mix, let alone being in coconut fibre. It was so wet for a lot of months.

To sum this hoo-ha up, I admit that I do not know nearly enough about the use of coconut and I am not qualified to make sweeping statements on its use. If you want to use it . . . do so at your own peril and good luck. Last thing I would say is this. How could a specimen sized hunk of D. speciosum var. grandiflorum, with 20 or so long fat bulbs, and racemes on board, stay upright in a pot full of mushy coconut husk? It might sit all right on the bench in your bush house but to transport it around . . . I doubt it.

Now, the most Important bit. Yes, I am giving up my secret weapon! I learnt this lesson the hardest way possible. I was, for a couple of decades, the laziest grower of D. speciosum you could imagine. I was always pretty happy with my results during this time. But I never seemed to get my best plants into the best show condition. It took eons to realise what my problem was. Two things eventually dawned on me.

Firstly, D. speciosum is a guts, it needs plenty of food in the form of fertiliser. Not just a spray with something once or twice a year, but a continuous regime of well balanced fertilising. This is a species that produces big heavy bulbs in the main, and it cannot do that without the building blocks of life . . . FOOD!

I have not got the patience to waffle on about N:P:K ratios and certain levels of calcium, or molybdenum, or the eyes lashes from a female zebra in season, blah blah blah. Perhaps, if you have a handle on this kind of science, you may win dividends on the show bench. Just maybe you might screw it all up too. But I am not a chemist and nearly failed science at school. I only know a few things that work well. Just fertilise all the time and vary what you apply. I do tend to use things that have added trace elements.

For three years now I have been committing the following feeding plan. I stick a handful of organic “stuff” in each pot. This may be blood and bone, dynamic chook pellets, or anything else with a bit of body that will not wash away through the bark at the next watering. I repeat this application when I can no longer see any of it left in the pots, but I use something different every other time. Never the same thing twice in a row. There is no science at all in this shattering plan of mine. I can hear you agreeing with me . . .

I have also started putting a cupful of long term Osmocote in the pots as well. I simply do not have time to mix up great amounts of water-soluble fertiliser on a weekly basis. In my case, that would be an all day job. However, once every six weeks or so, I make the time to do it, just because I turned over a new leaf a few years back and intend sticking with it. So Osmocote is letting out a little bit of oomph each time I water or it rains.

There you go. You have my secret and fiendish plan to conquer the show benches of the future. If more than this much work is needed, maybe I will scuttle the orchids and take up stamp collecting. As I said before, this is what I do now and results have been good in that short term, with big healthy bulbs the result. I hope the racemes will carry the flag for me. I will not claim that there are not better ways to feed your orchids. As I said, get onto Google, there is lots of info on orchid fertilising. They will have much more science in them for you to get happy on, if you think I might be wrong . . . perish the thought.

The second thing that I discovered once I slipped out of my lazy ways is this. You simply cannot grow good D. speciosum unless they have terrific and healthy root systems. And you cannot have healthy root systems if your potting mix is let go like mine was. I kept some of my plants captive in the same pots for up to 12 years.

Sharing some of the pots were Elk Horns, Birds Nest Ferns, Hares Foot Ferns and Rock Velvet Fern (Pyrosia sp). I even had a couple of tree ferns settled in. Worst of all was a vast assortment of weeds that eventually got so thick that I was forced to do an eight month long utterly destructive repotting of about eighty per cent of my entire collection. This required around seventy bags of orchid bark. Mrs Walsh has no idea how much of our hard-earned cash I shifted around like some of them shady characters in Wall Street movies.

After years of being left under these conditions the rot set in. New bulbs were not coming or started rotting before they matured etc. Ants moved in, slugs were all about, frogs took up residence and all sorts of caterpillars found safe quarters. I thought I saw a tree-kangaroo in their one day but this remains an unconfirmed sighting at this stage.

Eventually in my life, I started to hear rumours that there was a thing called pH. I listened to experts and read articles that I had skipped over for years. I worked out that my sodden, composted pine-bark\soil must have been pure sulphuric acid in the main. These days I have started to throw lime at the plants with great abandon. Others do it and so far I have not seen it causing any problems. I have never heard of soils or orchid bark turning alkaline, they only ever go acidic. Lime swings the pH back towards the good zone.

The other reason I now broadcast lime about the pots and the floor of the bush house is simple indeed. It gives me great pleasure to watch slugs and garlic snails racing around with their little bums on fire. Lime actually takes care of a lot of these pesky varmints that will feast on your racemes next season. It also has the effect of keeping a lot of fungal problems under control.

The message is this: DO NOT PUT OFF YOUR REPOTTING. You must do it when the time is right. Your instincts will tell you when that time is nigh. I have no intention of explaining how to repot your D. speciosums. Every plant will be different. And it is the type of activity that has to be demonstrated. Most orchid groups have demonstrations about repotting. I suggest that these would be the best way to learn about it. Once you see one demonstration you will have a skill for life.