naoki
Well-Known Member
Most likely the main problem is the availability of oxygen dissolved in the water, and of course if the "mud" is caused by bacteria consuming available oxygen, then your roots will suffer. Of course, such an environment may be typical for most broken down mixes and if oxygen is not alloewd in the pot, well, then the roots perish. In such a case it might perhaps be a better option to increaser watering frequency in order to refill with fresh, oxygenated water.
Lance, both watering frequency AND how long it takes to dry out influence the water (and nutrient) availability to root (I'm sure that this is obvious and you tried to simplify this). If the media is moist for a longer time, they can get nutrient/water longer. The stable moisture level is considered to be one of the reasons why addition of 30% peat to bark-based media caused faster growths in Phal trials (e.g. Wang 1995. Medium and fertilization affect performance of potted Dendrobium and Phalaenopsis HortTechnology 5(3): 234-237). The bark only media dries quickly, so they did water twice as much as the pot with peat.
But higher frequency of watering might result in more oxygen as Bjorn said. Do you really think oxygenated water makes difference, though? The amount of O2 water can hold is tiny (around 10mg/l). In broken down media (or potting soil), top-watering is supposed to help exchanging the air in the pot. But it's a bit hard to imagine that it is a problem in pretty coarse orchid media. Soil respiration is an interesting point, too. I wonder how much this soil respiration contribute to the O2 level inside of the pot.
I briefly looked for an O2 probe to measure soil O2 content. I couldn't find a cheap one, but it would be fun to test how different watering is influencing the O2 level in the pot. Here is one from Apogee for $300. But it's a bit too pricey for me.