To Fertilize or Not?

[qbie]

Originally Posted by WaterWitchin

Using tap water works for most orchids other than if high TDS you're going to fight mineral buildup.

I don't think I have especially hard water, but because we have similar weather conditions, I'm following the grower's habits the plants came from and between Nov-March, the only watering is what Mother Nature provides. Last Nov had several days in the 70s with only a few days rain so I think I will water more if there are any dry spells like that again, but would you agree the rainwater for these several months should flush out any potential mineral buildup?

[estación seca]

I seem to recall San Francisco's water is not high in dissolved minerals. You can find out. Go to your water utility's Web page and look for their annual water quality report.

If you have a winter with a good amount of rain most other orchids will struggle in the cold and wet.

[Roberta]

I wouldn't worry about water quality even if you aren't in the city - surrounding areas have a range of levels of solids in the water. But these are not sensitive. Mine get city water and they are fine. When you say "San Francisco Bay area" that covers a huge range of microclimates, so you do need to be a bit more specific with regard to what you experience in terms of temperature ranges.

[WaterWitchin]

Originally Posted by WaterWitchin

Using tap water works for most orchids other than if high TDS you're going to fight mineral buildup.

Originally Posted by qbie

I don't think I have especially hard water, but because we have similar weather conditions, I'm following the grower's habits the plants came from and between Nov-March, the only watering is what Mother Nature provides. Last Nov had several days in the 70s with only a few days rain so I think I will water more if there are any dry spells like that again, but would you agree the rainwater for these several months should flush out any potential mineral buildup?

That was a generic statement. You have to follow what's in your own local environment. No idea whether your rainwater flushes out potential mineral buildup. That depends on too many variables, including medium, the TDS in your own location.

I grow almost everything in semi-hydro. If I used straight tap water from MY tap, I'd have lots of mineral buildup in a short period of time, on LECA, which would have an effect on its porosity. I would have to repot more often, which for some orchids isn't a good idea, or something I desire to do frequently. I grow exclusively inside now. When I grew outside it was a garden hose. We don't get enough rain to depend on for orchids.

So any advice you take, you have to factor in YOUR environment and other cultural differences. It's just generic suggestions to adapt to your specific conditions. I grew in bark for a decade or two, outside half the year, in a basement the other half, only used tap water, and that was a whole different ballgame. The learning curve switching was quite the trip, and I never even left the farm.

[Ray]

Originally Posted by qbie

I don't think I have especially hard water, but because we have similar weather conditions

The weather only affects water hardness if your supply is surface water. Most is taken from aquifers underground, so the local geology id what affects it most.

[qbie]

OK, so I've had this burning question. Human urine (diluted) is a great source of nitrogen for the veggie garden. So why doesn't anyone use this for orchids? I assume it would need to be diluted even more for orchids since they don't need nearly as much food as plants that grow more quickly. Urine concentration can vary depending on our hydration status. Do all these make using even diluted human urine too unpredictable a concentration (unless you can analyze it in a lab) so it is not practical for orchid use, lest you run the risk of burning them?

[Roberta]

I think you explained the reason... it's unpredictable. This is the case with all the rest of the "organic mixtures" that people come up with too. Fertilizers sometimes have their nitrogen as urea, but the amount is known. And orchids need very little. Why would you risk your plants to avoid spending a very few dollars on a bottle of fertilizer that will last for months or more.? Compared to the price of orchids, fertilizer costs nearly nothing.

[estación seca]

With a modern diet human urine contains so much salt it is harmful for most plants.

[qbie]

Thanks everyone. I just remembered Roberta recommended the book "A Bay Area Guide to Orchids and Their Culture" and it notes which orchids are very sensitive to TDS. Fortunately Sarcochilus and the others I have are not among these.

[Ray]

One more thing about urine- the nitrogen source is urea, which is not particularly well absorbed by orchids.

There are three types of nitrogen absorbed by plants, nitrate, ammoniacal, and urea. The first two are preferentially absorbed by the roots, but foliar uptake is poor. The opposite is true of urea - it is preferentially absorbed through the leaves, but less so by the roots, unless it has been decomposed to ammonia, a slow process, more so if the medium dries.

The problem is that many orchids, especially as they mature, develop waxy cuticle layers on the leaves that limit foliar uptake, if not prevent it.