Hell bent on making my orchids the happiest plants around and expecting them to return the favor with long-lasting, floriferous blooms, I now water primarily with RO reverse-osmosis water - ie, pure water without salts. I also know that there's no way I can fertilize everybody as often as I should, so I tend to add Osmocote a time release fertilizer into most pots. It lasts for about 4 months, and provides steady, low levels of fertilizer in between my less frequent fert sessions.

I have managed to scorch a number of plants with horrific fertilizer burns, and many with lesser burns, and it's puzzled me. I now know which Paphs and Phrags are very fertilizer intolerant, and I've tried to go lightly with those. I tend to add a bit of the Osmocote and skip the other ferts altogether.

But I still couldn't quite explain why the plants were so pissed. In discussing fertilizers with Lisa up at the Dartmouth greenhouse, she let me on to a really interesting factoid. Through experience, she's found that when watering with RO water, time-release fertilizers do not behave as expected. Rather than release their nutrients gradually over a four month period, the pure water tends to pull all the fertilizer out at once. POW! Your plants get hit with a salt blast that rocks their poor little roots and leaves. And it doesn't rock them in a good way.

These time-release fertilizers are designed to work with normal tap water, which is full of impurities. Combine them with pure water and all the stuff inside those time release granules simply busts down the door trying to achieve what the fertilizer thinks is a balanced concentration. Pure water + way too much fert = normal concentration.

So, important note to self: DO NOT USE time-release ferts with RO water!

Julie