ORCHID COMPOSTS Whatever medium is used it MUST drain efficiently as most orchids hate to have wet, soggy roots. Bark: This can be of various types e.g. fir, redwood, cambark. It can be obtained in fairly large pieces, medium and fine. It can be used on its own or with one or more of the following added - osmunda fibre, charcoal, peat, coir, sphagnum moss, perlite, foam rubber and grit. All of these aid drainage and help to retain the water for a short period. Usually the larger the roots, the larger the bark pieces will be. The finest bark is best suited for seedlings. Rockwool: This together with Grodan (almost the same but with nutrients added) is spun from volcanic rock and has become popular over the last few years. It drains well, yet retains water for a short while. Even Rockwool which is kept quite moist does not seem to be much of a problem as there are sufficient air spaces to compensate. Feeding can be a little tricky as some calcium needs to be added when watering most orchids. Coir: Coir comes from the husk of the coconut. It holds water but has plenty of air space and has proved an excellent medium for small seedlings or for re-rooting plants. Coir can be purchased from specialist orchid Nurseries. It can be purchased in blocks, which when water is added, will produce approximately a 2 gallon bucket of compost. There is quite a large amount of salt found in the block coir and it needs to be washed thoroughly before using. This type of coir is often scraped up after the rest of the coconut has been used. Other more expensive coir can be obtained from orchid Nurseries and can be purchased by the bag or mixed with foam pieces. This type of coir is coarser and is the first to be obtained from the coconut and therefore contains very little salt. It is my experience that this type of coir is excellent for Phalaenopsis and the finer coir block compost providing it is washed is excellent for all seedlings and for Phragmipedilums. Stone Chippings and Seramis These are not very widely used yet in the U.K. although more people are experimenting with seramis and this hydroponic method of culture. With Seramis a special guage is needed which indicates when the plant should be watered. A special seramis feed is given on alternate waterings.I have found that the reverse is true with Seramis providing the true hydroponic method is adoped. Watering needs to be carried out less often. Charcoal Although not widely used in the U.K. charcoal is used quite often abroad. Its benefits are much the same as those given under ‘Stone Chippings’ above. Moss and Perlite This is a wonderful medium for most orchids and is most desirable for Lycastes. I now grow Lycastes with moss and perlite in the top third of the pot followed by a layer of bark which is on top of a layer of polystyrene pieces. It is very good for re-rooting plants and for any plant with small, fine, roots emerging from pseudobulbs. A word of caution when using moss and perlite - it can remain quite wet at the bottom of the pot when used alone. It can be great fun and very enlightening for an orchidist to try all these composts to discover which is the best for the conditions of his/her own orchids and environment. Alpine Grit With many other orchidists I now use Alpine grit for growing some orchids. I suppose about 25% of my orchids are now grown using this medium with very good results. If you consider that in their natural habitat many orchids experience a deluge of heavy rain followed by a dry period, this medium is a good choice. |