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Potting Mixes and Watering Regimes

Author: John Ryan, Supplementary note to Bulletin, Vol 20 No 3, May-June 2005.

At the March meeting we discussed potting mixes and watering regimes.

I thought I might add my penny's worth to the discussions.

The one thing about growing orchids is that it's difficult to be dogmatic. Everyone's collection is different. Some have large collections, some have small collections, some have a glasshouse, some grow in an area in their house, some grow terrestrials, and some grow epiphytes. Our individual circumstances are also different. So what suites me in terms of orchid culture isn't necessarily right for someone else. Epiphytic orchids can either be mounted, potted or some cases just hung up to grow on their own. I will limit myself to discussing potted orchids.

Most potting media is bark based. It is easy to use and until recently, fairly easy to obtain. Most importantly orchids generally like to grow in it. I have been growing orchids for nearly 30 years. I grow an eclectic collection of different genera that seem to grow well as a mixed collection. I grow Australian dendrobium species and their hybrids, cattleya, laelia and sophronitis species and mini-catt hybrids.

My glasshouse is 32' x 16' and is as full as it can get.

I have seen a number of potting mix fads come and go and I have tried a number of different types of mixes and additives. At one time I was told that dead bracken fern was good to add to the standard bark mix, so I spent weekends collecting it, cutting it up and mixing it in with the bark. It didn't make any difference and was too labour intensive. Charcoal is another additive which it is good but can be difficult to get. Some people use Styrofoam. I tried the beads which are available for use in bean bags. The problem with them is they stick to everything and you only have to get a breeze when you are potting and they go everywhere. The crunch came when my wife removed some of them from my then infant daughter's nostril. It was politely suggested that I get rid of them, which I obediently did!

So what do I use? I use treated pine bark mixed with pebbles for nearly all my plants. The pebbles and bark are mixed on the basis of 40%:60% by volume (or whatever looks right at the time). Some plants seem to like a higher percentage of pebbles, namely the rupicolous laelias. I use medium size bark for all plants except the larger pots of mature Dendrobium speciosum where I use a mix of medium and coarse grade bark with the medium size pebbles.

I do not wet the mix before use, but I do water the pot after potting to wash the dust out. Sometimes this doesn't happen until the collection is next watered. The pebbles can be bought from most landscape centres either in large plastic bags (approx $10) or more cheaply in a garbage bin ($1) or bucket (nothing, if you're a smooth talker). I use quartz pebbles or blue metal which I find equally as good (don't collect it from the side of the road!).

Why the pebbles? Firstly, and most importantly my plants grow well in a pebble and bark mix. It provides good drainage and doesn't break down too quickly. Secondly, bark is expensive and by mixing it with pebbles it goes further. I have been using this same basic mix for 20 or more years and it continues to serve me well. What failures have I had? There are 2 bark types that don't work well in my conditions. They are boiled bark and composted bark. I water erratically, sometimes once a fortnight at other times every day depending on work commitments and the weather. Boiled bark dries out too quickly and I can't get it to retain moisture once this happens. Composted bark just rots down when watered and turns to mush killing all the roots. The best bark I have ever used was Californian redwood bark. York Meredith in Sydney used to import it. Unfortunately it is no longer available.

Some plants I grow in sphagnum moss. This is generally restricted to mini-catt seedlings and any plants that are looking sick. The sphagnum is loosely packed in the pot and topped off with a layer of pebbles to stop slime growing. The mini-catts only stay in the sphagnum until they are growing well, when I move them into my standard mix. As mentioned above, I water erratically. However, when I do water I water heavily, that is until the water runs through the pot. Everything gets watered at the same time. I water with tank water Summer and Winter. None of this standing a bucket of water in the glasshouse to warm up - I don't have the time.

If plants are looking a bit desiccated (it is usually the pots of large Dendrobium speciosum) they are stood in a bucket of water overnight. The same goes for plants in sphagnum moss. The moss once dried out is hard to wet again, so they also get dropped into a bucket of water overnight. I will often drop mounted plants into a bucket of water for the night as well.

There is some good advice on potting mixes and orchid growing in general on the Down Under Natives Orchids web site at: http://www.duno.com.au/growingtips.htm.

Good growing.

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