For a long while in my houseplant career I used shop bought potting mixes just as they are, straight out of the bag. This includes a variety of brands of Orchid compost, Streptocarpus and gesneriad compost (I don’t grow many gesneriads anymore; something had to give), cactus and succulent compost (I don’t grow these anymore either to speak of), et cetera, et cetera. I have now taken to producing my own mix from separate ingredients, and I have to say I have much better results. I think, during this article, I will outline my experiences with the various potting mixes and state my reasons for liking or not liking them. I should stress that my methods work for me, but may not work for the reader. This is a long article, so today I’ll talk about orchid potting media, with parts two and possibly three in the coming days.
Orchids
As this blog is going to feature a lot (a LOT) of orchids, I shall start there. There are several brands of orchid compost on the market, and they all have their uses, but not necessarily for orchids.
Firstly, there is the bog standard orchid compost from Westland, Levington or J. Arthur Bowers that can be purchased from practically any garden centre. When I first started growing orchids 15 or more years ago, I didn’t realise there might be other mixes out there. For my liking, it contains far too many ‘fines’ to be of any use whatsoever for orchids (it does have other uses, I’ll come to that shortly). They seem to contain a percentage of peat, so they hold too much water and are far too dense. They do contain bark chips but they seem to be of a variety of grades, and the coarse ones float to the surface like Brazils in a nut mix. So, as you get down the bag, the mix gets finer and finer. The only way around this is to either shake the bag or empty it out and mix it up properly. Even correctly mixed, I don’t think this mix is appropriate for orchids. However, that’s not to say that it doesn’t have its uses. It is fantastic for Anthuriums, and passable for Cymbidiums, too. The problem might lie in several places. Firstly, in the original mix itself. Secondly, there is no way to know how old the compost is, since all bags look alike unless there has been a rebranding. People generally don’t realise that compost doesn’t keep forever, and specialist mixes for even less time. They continue to decompose in the bag and the result of this decomposition is fines. I have found compost worms in bags of orchid compost in the past. Thirdly, we need to know how the garden centre has stored the compost, and where. Again, few people realise that bags of compost shouldn’t be left outside unless they can be protected from the weather, specifically rain and frost. They absorb lots of water. Orchid compost should really be kept indoors and relatively dry. The bags are perforated and absorb water like a sponge. The result of this is, you guessed it, decomposition resulting in fines. This compost usually comes in 10L bags which is quite a lot of compost if you have only a few orchids.
Next we have a mix that comes in smaller bags, usually branded Lorbex, and sold in quite small 2l bags. this mix still isn’t quite right for me, but it is much better. It seems to me made of fairly fine bark chips with a proportion of perlite added. There is no peat added so it drains very nicely. At least under my conditons, the perlite isn’t necessary as I don’t need the extra water storage capacity. This compost doesn’t come from a major compost supplier (when I worked in that trade, it was supplied by the garden centres supplier of Bonsai trees and accessories), and doesn’t appear to have been stored outside. It is always dry (as it should be) and ready to use after a brief moistening. With careful watering, most orchids will do well in this mix. Being in small bags, it is ideal for people with only a few orchids to repot. Keeps well provided it is kept indoors and dry.
Then we have the new kid on the block. Orchid Focus. I have to say that I personally don’t use this, but I have heard other growers saying how wonderful it is. It seems to be a broader mix which includes coconut husk. Coconut husk is basically the fibrous outer coating of the coconut so is a by-product of the coconut industry. It is reputed to have excellent water retention and aeration properties, ideally suited for orchid culture. It always used to contain a lot of salt and needed very thorough washing before use but I assume that is now done before the product is sold. The main reason I haven’t got involved with coconut husk based potting mixes is that I had already found a mix that suited me, and I like to grow all my orchids in the same mix so that they dry down at the same rate. A major grower in the UK uses coconut husk exclusively and swears by it (all this means for me is that if i buy any of his plants I have to repot them immediately). Orchid Focus is found more and more in garden centres now, and is a perfectly good orchid growing mix. All I would say with regard to potting orchids into it is that all of the old mix should be removed from the roots, as mixing different styles of compost is never a good idea. For my own personal use, I find that it retains too much water so it doesn’t suit my watering regime.
Lastly, I’ll talk about the mix I like to use (well actually, it isn’t a mix at all). I guess in many respects I’m quite old fashioned as I still like to use bark chips. I should make a distinction here as it is possible to buy bags of bark chips from the garden centre, but they are entirely unsuitable for many of the reasons outlined above of being cold, wet and too composted. also, the chips are usually too big and may come from many varieties of tree, resulting in them being very resinous (you can often smell it when you open the bags). My potting medium of choice for orchids is Melcourt orchid bark. It is available in three grades; fine (for seedlings), medium (suitable for most orchids in 12cm pots) and coarse (ideal for large plants or plants that need extra drainage). At least one large orchid nursery in the UK use the same, and a lot of my orchid collection has come from them (so I don’t have to repot new plants). Melcourt bark chips are of uniform size with low fines which can be used straight from the bag. I like its water retaining properties, not too much, not too little, and I don’t need to add any other elements. The fine bark chips I don’t use for orchids so much as I tend not to grow young plants or miniatures but I do use a lot of it as an additive in my standard houseplant potting mix which I’ll come to later. The only real downside to Melcourt bark chips is that they aren’t found in garden centres. I’ll say that if you have any more than a passing interest in keeping your orchids alive, you’ll root this product out. I buy it from a wholesaler by the 70 liter bag, but this is a bit excessive for small collections! It is sold in smaller quantities by a couple of orchid nurseries. It seems to stand up well for a good couple of years without breaking down, so it is suitable for the more difficult of orchids that resent frequent potting. There are usually a small amount of fines at the bottom of the bag, but this can be easily riddled out, and is just a result of the contents settling a bit in transit, and is not a sign of composting. It is important to keep this product dry to prevent composting (you can often see the fungal filaments in potting medium that has begun to decompose). I tend to keep it indoors in my growroom so it is there when I need it, though I suppose there may be people who would come up with reasons why I shouldn’t.
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