MSU fertilizer concentration in winter for Catts
 

I grow my Cattleyas in a relatively mild climate in the winter. I would like to know if anyone has an idea the EC (electrical conductivity) my water should be using MSU fertilizer. I use reverse osmosis water. Thanks in advance.

I use the same formulation winter and summer, just tend to fertilize less often in winter (and water a little less often since things don't dry out as fast). Many Catts are actively growing in winter, for some it is even prime rooting time.

The only exception to the above is probably some of the species Cattleyas (like dowiana) that have a resting period. I tend to give my Cattleyas a constant supply of calcium and then fertilize them when they are actively growing. When the growth has finished or is nearly so, I stop fertilizing. For those Cattleyas that are always pushing new growth, fertilizing year-round is perfect.

Good point on C. dowiana... I don't grow that one. It does have special needs. Just in general, when a plant is growing, it need fertilizer. And more Catts than not are growing through what passes for winter at my house.

I vote for minimal fertilizer all the time, with the frequency controlling the net mass applied, as Roberta described. I always shoot for about 100 ppm N applied over a week when conditions are good, as I have a varied collection with something actively growing at all times. At that low concentration, I have seen no negatives of feeding stuff that's not growing, but keep in mind I grow nothing that goes truly dormant, that might be.

For MSU RO fertilizer, the EC for 100 ppm N is 0.8 mS/cm, added the the EC of the water, so you can factor your feeding frequency into your desired level.

Since I use RO water, I'm not sure using this water in order to "stop fertilizing" is such a good idea? It contains nothing whatsoever. I heard that is not good for the plants? Thoughts on this?

There's always the method of using one or a few orchids for trials. Use a relatively weak solution.

I'm just wondering if using RO water is like humans continually drinking distilled or deionised water. Not good after a while.

There is nothing wrong with using - or drinking - purified water.

There is a myth about it "extracting" minerals from plants, but that is just plain incorrect. First of all, let's not forget that the rainwater they get in nature is about as pure as RO water (i.e., ~10 ppm or less) for the first few seconds after the rain begins, and then it is purer than that for the duration. Plus, what chemical process within a plant would allow mineral extraction when the plant breaks down the water for use?

The only thing "bad" about using purified water to drink is its taste - it absorbs carbon dioxide from the air, forming the very weak carbonic acid, so has a sour taste.

I fertilize with 50 ppm nitrogen year round. I use the MSU formulation for RO water. In winter I feed a little less frequently, using plain RO instead.

I took a look at some information about distilled water and human consumption of it. The details suggest that it's ok to drink it in general - ie. maintain regular intake of regular food, and it should be ok. On the other hand, people probably shouldn't take things to extreme - such as permanently drink distilled water - regardless of what diet we're on - just in case.

For orchids - if using purified/distilled water works well for any particular method of application, then that's fantastic.