The problem with soil moisture meters is that they are meant for regular potting mixes and not bark based mixes. Chunky porous mixes have too much air in them and they will severely skew the readings. Even in soil, they work by measuring electroconductivity and this gives only a very rough approximation of actual moisture levels. If your friend's orchids are potted in bark, it's just not going to work well.
Could she use bamboo skewers instead? A lot of people use these to determine when to water. They can be left on the pots and pulled out occasionally to check how damp it is. The only trick is knowing how dry it should be before watering again depending on whether it's an orchid that likes to dry out or stay moist.
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Camille
Completely orchid obsessed and loving every minute of it....
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