In the previous century the emphasis was on using synthetically manufactured chemicals for pest control and production of synthetic fertilizers was subsidized in many countries to increase production. Even though we saw amazing results, however in the long run these harmful proved for the natural and beneficial insect population, consequently negatively impacting the ecological system. The trends have now shifted to adopting traditional methods of growing plants, even for orchids. Efforts are being made to gather as much traditional knowledge as possible.
In place of synthetic pest control drugs (insecticides/pesticides), many natural methods are getting adopted which does not harm the plant friendly insects. One such method is of using ash as pesticide, fungicides and an another probably use as a fertilizer. Ash, in particular wood ash is alkaline in nature and is high in minerals. It is observed to possess a significant percent of Calcium, Potassium, Phosphorus, Aluminum, Silicone as well as Iron. Ash from fresh and seasoned wood possesses a higher Iron percentage. How does it work? It is observed to kill insects by drawing water out of their bodies. This acts as a deterrent to pests like slugs and snails as well as insects that inhabit the outside of plant body.
Method:
Ash can be used on all parts of the plant. Sprinkle a layer of ash around the roots. Some ash can also be sprinkled on the leaves. Use of ash is not one time affair, it needs to be repeated twice weekly. If it gets wet then, it loses its efficacy, so needs to be repeated. However, ash should not be used very frequently, as it will increase the pH, which can be harmful for orchids, especially those that prefer a lower pH.
Precautions:
Most orchids grow between the pH range of 5.5 to 7.5 and ash being alkaline can be safely used in small quantities on most of the orchids. However, it should be avoided on orchids that prefer acidic conditions. Orchids like Cattleya lawrenceana like to grow in extremely acidic conditions and would show signs of distress with ash application. So please check the pH requirement of your orchid before using ash on them. Some people recommend mixing sulphur with ash can balance the pH, but use with caution.
Source of Ash: Always check the source of ash before using it on orchids. Using ash from painted, chemically treated or oil applied wood can be harmful rather than beneficial to the orchids. Do not use ash of cardboards, or any such material or even trash, as the ash from these would be containing harmful residues.
Ash as fertilizer: A mixture of ash and compost when applied to terrestrial orchids worked well with the orchids. Its a rich source of Potassium which promotes roots growth. Other minerals present in it are also beneficial to growth of orchids.