Quote:
Originally Posted by orchids3
Wheather or not to use urea based fertilizers(on Orchids) is a debate I have heard often am not convinced either way. My understanding is that Urea has to be further broken down by bacteria and the rate of breakdown depends on temperature. My conclusion has always been that Nitrates and ammonia fertilizers can be directly used by orchids and require no further breakdown - therefore may be better but only because of the rate fertilizers are flushed out of pots by watering. Urea may not do as much good because it may not stay around long enought to be broken down. Thats my two cents worth.
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I've been doing some research on this, and it seems that everything is a matter of degree.
Urea can be absorbed directly through the roots, but only at a very low rate. It is pretty good as a foliar feed however, as it moves through the ectodesmata pretty readily. Once it decomposes, the urea breakdown products (mostly ammonia) can be absorbed by the roots. The argument seems to be simply whether that happens sufficiently in an orchid-pot environment.
Nitrates and ammonium compounds are poor for foliar feeding, but are readily absorbed by the roots. Nitrates are known to give more compact plants, for some reason I haven't found yet.
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