BOLTERS and RUNTS by Brian Milligan
Human nature being what it is, most of us believe that our orchids are not growing as well as they should. We might be pleased with the growth rate of a few but are less happy with all those that don't grow as well. However, if you stop to think about it, why should all our orchids grow at the same rate? Only in the case of a batch of mericlones, which are genetically identical, should all orchids respond equally to a particular cultural regime. When it comes to seedlings, even of the same grex, we can expect to find both 'bolters' and 'runts' among the progeny, much as we would like them all to be bolters that grow rapidly and flower early.
Growers of species orchids are often encouraged to replicate the conditions under which their orchids grow in nature if they wish to grow them to their best potential. In my opinion, this information should be regarded only as a guide, particularly with regard to the temperature range to be provided and the observation of a 'rest period' when the orchid should be watered less frequently (usually during winter).
We can, in fact, grow many species orchids in cultivation far better than they grow in nature, primarily because of the law of averages. As any student of the weather knows, there is nothing more variable than the weather, especially if one lives in Melbourne. In nature species orchids must survive dry spells when the weather should be wet, and also unexpected wet periods during the supposedly "dry" season. Yes, most orchids survive these unexpected seasonal variations, but obviously they don't grow as well as in more favourable seasons. It's therefore quite reasonable that they should grow better in our temperature-controlled glasshouses, provided that we water them regularly when they are in active growth and withhold water when they are at rest.
Scientific studies of species orchids in the wild have shown that their seedlings grow much more slowly than do artificially cultivated seedlings that are watered and fertilised regularly. In fact, some species orchids in nature may take several times as long as cultivated species to reach maturity, and it has been estimated that some specimen cattleya species found in nature may be a hundred years old or more! Reasons for the slow growth of wild species include not only unfavourable weather conditions but attack by various insect pests and grazing animals, and by lack of fertiliser, which is limited to that provided by passing bird life and water draining through dead vegetable matter trapped in tree forks.
Fertilisers make a big difference to an orchid's growth rate, provided that they are applied at an appropriate concentration and at the correct period during the orchid's growth cycle. Fertiliser composition is also important. Nitrogen-rich fertilisers will promote excellent leaf growth but may retard flowering and it's generally regarded that 'balanced' fertilisers (made of a blend of chemicals that provide the orchid with appropriate levels of nitrogen, phosphorus and potassium) are best. "Weak and often" is good advice when it comes to fertilising orchids, as a grower may cause more harm than good by applying liquid fertilisers at concentrations that the plant cannot handle.
In conclusion, there are many factors that affect an orchid's growth rate, not least genetic diversity - some seedlings will grow better than others, regardless of the grower's cultural skills. Be prepared to cull some of the 'runts' from your collection each year (they take up just as much of your time as the 'bolters'), and put the space that they occupied to better use, for example, by purchasing some new hybrids or (even better) a line-bred species orchid!