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Fertilizing a mounted orchid

  • Thread starter schmiggle
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I've had an Aeranthes ramosa for a little under a year, in which time I have never fertilized it. Several months ago I moved it from a pot to a mount for the sake of convenience, because the orchid bark would fall out whenever I watered. After getting the plant stable, it began to grow much more slowly than before, I assume because the urn it's on doesn't break down and release nitrogen. So I now have a 30-10-10 miracle fro orchid fertilizer that I've diluted to about one half two thirds strength (I was trying to make it full strength in half the recommend amount of water, but I ended up less than half filling the measuring cup).

I have two questions. First, I spray the orchid twice a day rather than watering, because it needs to be kept constantly moist. What I've been doing is alternating between fertilized and unfertilized water, so that I can wash away salt build-up. However, am I washing away the fertilizer by doing that? Alternatively, am I fertilizing too often? I know weekly is often the fertilizer suggestion, but I suspect that I spray too little of the fertilizer solution at a time for that to be effective. Second, should I further dilute the fertilizer? I've read this species should be fertilized lightly, but I don't have a good sense of what that means, or if it means how often or how much.
 
Several months ago I moved it from a pot to a mount for the sake of convenience, because the orchid bark would fall out whenever I watered.

That makes me wonder how you were watering in the first place. A small piece or two once in awhile is one thing, but every time?

Is the urn a porous material like terra cotta?

Did you utilize any moss on the mount?

What is your humidity like?


After getting the plant stable, it began to grow much more slowly

It is possible that a decrease in nutrient availability is the reason, but it may also be due to the roots drying out much faster than before.


So I now have a 30-10-10 miracle fro orchid fertilizer that I've diluted to about one half two thirds strength

Orchids are designed to get by on less fertilizer than many plants. You are likely to do far more damage than help with a more concentrated fertilizer.

Yes watering with pure water will wash away any fertilizer residue .... which is exactly what you want.

Some species are easily harmed by fertilizer in concentrations which other orchids can handle. (Masdevallia are an excellent example.) With such plants, it is always safer to use too little than too much. I have not grown that species so cannot give you more than general information. If your plant is among those which needs onlynvery light fertilizing, then that could mean 1/2-1/4 strength (possibly even less) as occasionally as every fourth watering. You may have to do some experimenting.
 
I've never grown an Aeranthes, but I have several vandacous Orchids, and an angraecum, which is a close relative. I read up on your orchid too. It likes it wet - one grower leaves them in saucers of water, but they rot easily if too wet. They need constant humidity of 80% or higher (that's probably why that one grower has them in saucers - I would not recommend it) and are a lot like their relatives in having a very sensitive root system. It's sulking from your repotting. It may take months to start growing again. When I got my Angraecum, it took about three months before it adapted to my backyard - and that shock was without repotting.

Vandacous Orchids are heavy feeders, so you can probably fertilize this one almost every time you water - but at 1/4 strength.
 
That makes me wonder how you were watering in the first place. A small piece or two once in awhile is one thing, but every time?

Is the urn a porous material like terra cotta?

Did you utilize any moss on the mount?

What is your humidity like?
I at first had it sitting in saucers of water, but I became concerned about root rot so I started top watering daily. I wouldn't lose a ton of substrate every time, but the pot was very small so it added up fairly quickly.

I now have it on a terra cotta urn that I fill with water. It's an urn intended for plant watering--you fill it with water and stick it in the ground. However, I glued the plant to the urn using krazy glue (which has turned out to be a mistake, but is not toxic), which I think prevents a lot of the water from coming out on the side with the plant. Ironically, the other side is much moister.

I have sphagnum on the roots, when I didn't the plant would drop a leaf every few weeks (though miraculously it still grew during that time).

My humidity is definitely much too low, I'm going to move to a terrarium soon and then measure. I had it over a saucer of water previously, which definitely increased the humidity (of the whole room, actually--I stopped that partly because it was bothering my roommate, though rot was also a concern).

My feeling is that the roots are moist enough now because it hasn't dropped any more leaves, but I could be mistaken.

It's sulking from your repotting. It may take months to start growing again. When I got my Angraecum, it took about three months before it adapted to my backyard - and that shock was without repotting.
That's good to know. I suppose it will do everything very slowly.

I'll dilute the fertilizer down to 1/4 strength and continue to feed on the schedule I've been using. I'm sure it would be happier in higher humidity, and it probably won't flower until it's there, but I have to set something up first. Given that it doesn't need to much light and likes heat, I imagine it won't be too hard.
 
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Well turns out, after measuring, that I way underestimated how much I diluted the fertilizer. My guess is it was already at 1/4 strength. However, I will have it all replaced tomorrow with properly measured amounts. I also have a nice windowsill greenhouse lying around that I forgot about :headwall: so after measuring the humidity in that I'll probably use it.
 
Sounds like you're making progress! Let us know how it turns out! I'd never heard of this one before, but I'm going to be looking for one now!
 
Krazy Glue was indeed an unfortunate choice. When mounting an orchid, one typically ties the plant to the mount. Fishing line is typically the binder of choice though I use thread. Doing so allows the plant's roots to be in direct contact with the mount. In the case of a porous material, water movement to the surface can then provide some moisture to the roots.

Do not put the plant in the "windowsill greenhouse" until you ascertain what the temperature highs within the greenhouse are throughout the day. If sun shines directly on it, then it will almost certainly get far too hot.
 
Some people talk about fertilizer "strength", but I'm not sure how much you are giving. Most of the time we talk the dilution of fertilizer in terms of nitrogen concentration. So in your case it is about 132ppmN, which is way too high. I'm guessing 1/3 tsp of 30-10-10 per gallon? The good fertilizer concentration also depends on EC of your water (I'm assuming that you are using tap water since Miracle Gro isn't RO formula, i.e. lacks Ca etc). If you are using RO, you can put more fertilizer (but you need other fertilizer formula, or add back some tap water if you want to use Miracle Gro).

Most people recently goes around 30ppmN at every irrigation for majority of orchids. So 1/4 tsp per 2 gallons of water (25 ppmN) is good. For mounted, you can go with a bit higher concentration, but since you are growing it in windowsill, it is unlikely that fertilizer is the limiting factor. Due to low humidity, and probably not enough water, photosynthesis is likely to be limiting, so no need to give a lot of fertilizer.

Ray's website has lots of info about orchid nutrients: http://firstrays.com/free-information/feeding-and-watering

I have a couple Aeranthes (including A. ramosa), but I grow them all potted in medium bark based media. You shouldn't keep them moist all the time, but they do seem to like more stable potted environment. I grow it at the warm-end of intermediate temp (65F min.).

I hope yours will do well. The green flower color of this species (some are darker than others) is very nice!
 
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I now have it at 1/4 teaspoon in 1 gallon, which puts me at 97.7ppm. To get near 30ppm, I would have to dilute to at most a third of current concentration. However, I have been irrigating without fertilizer every other watering. Given how often I water (spray to dripping 2-3x daily), I think I want to continue this--I imagine that I end up adding more water than I would if I was watering it potted. However, I will dilute to 1/4tsp in two gallons, which should bring me to about 50ppm--I imagine that will be suitable for fertilizing every other time, especially since I will be washing away a lot of the residue.

With regards to how often I water: you say not to keep them constantly moist. I never let the sphagnum dry out completely--should I start? This plant has tended to like things on the moister side, though I imagine with higher humidity that will be less of a problem. Because I don't have a lighted terrarium that doesn't get too hot immediately available (dragonseye was 100% right in this regard), I'm going to humidify the room until I make one and adjust the watering schedule accordingly. I will see what that does to the watering schedule. I am watering with tap water, but I think the fertilizer actually has got a bit of Ca (will confirm when it's in front of me). My tap water is very soft, though, so I think it's all for the better.

Lesson learned: Aeranthes really do better potted. :p I don't think there's really a way to switch mine back at this point, though...I'll probably add more sphagnum to increase the stability of the root conditions. There's no way to non-toxically (to the orchid) remove the krazy glue, right? I know it hardens in water, which is the reverse of what I need from it.

Thanks for the help, everyone! Naoki, I too hope it does well. The amazing thing is that it's alive at all.
 
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Well, no Ca in the fertilizer after all. Hopefully my water is hard enough that it won't be an issue. I suppose the urn might also be leeching calcium.
 
  • #11
I'm guessing 97.7ppm is approximate TDS (from a TDS meter), which is different from nitrogen concentration. TDS is an important factor, too, but I was talking in terms of N conc. (most agricultural/horticulural people use it as the measurement of fertilizer strengths). Ray's website has an approximate calculater (you give N-P-K, and tsp/gallon, and tells you "approximate" ppmN). So you are using it around 50ppmN every other water, which seems to be reasonable.

If you are using tap water, there should be enough Ca (unless your water has extremely low TDS), and miracle-gro will be ok. No, ceramic won't leech sufficient Ca.

If it isn't drying out within a day, maybe you have high humidity. Or maybe you are using a giant mound of sphagnum. So it will probably grow well.

If you can, you should timing the water so that you water just before inside of the sphag becomes almost dry. But they can acclimate to your schedule. With mount, it is difficult to suffocate the roots, but if you keep it too moist in the pot, you can easily suffocate the roots.
 
  • #12
I don't have a TDS meter, but my guess is that the water can't be that soft, because Boston water isn't treated beyond ozone and UV treatment, and I imagine the reservoir already has some hardness just by being a sedimented lake. But I'm not positive how that works.

As far as sphagnum dryness is concerned: I'm not sure what you mean by totally dry, it certainly dries out over the day but still has a characteristic dampness that's gone if you leave it over a couple of days, in which case it becomes dry enough that it's hard to rehydrate. But it might be gettin high humidity. I don't think I have an especially large amount of sphagnum, but what I do have seemed to like being humidified last night, as some of it turned bright green again (much of the sphagnum is still living because I took it live out of a sundew pot).

Speaking of humidifying, my humidifier is shockingly effective, to the point that I woke up this morning and the room had reduced visibility! I imagine the humidity got well above 80%, so this seems like it will work until I set up a terrarium.
 
  • #13
Oh, so you measured the weight of 1/4 tsp of fertilizer to get 97.7ppm?

Yes, you probably don't have to worry about the 3 missing essential elements in MiracleGro: Ca, Mg, and S. If you do, you usually can get the water analysis from your water supplier. e.g., here is one from Wellesley, MA: http://www.wellesleyma.gov/Pages/FOV1-0001FDB3/waterreport

As a reference, if you use MSU at 30ppmN, you'll get about 30, 5, and 0.2 ppm of Ca, Mg and S, respectively. Wellesley water provides sufficient amount.

You are right, there are different level of driness, and it is difficult to describe. There is a technical definition of too dry for the plant to get any moisture (based on something called water potential). But I (or most orchid growers) call it dry, when it doesn't feel moist when you touch it. When it is moist, your finger feels it to be cooler than air temp.

But, I guess that it isn't behaving like the normal sphag since it isn't dead yet.

Be careful with the room humidity (for your health and house).
 
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  • #14
Thanks for the info about the water. With regards to ppm: I didn't weigh the fertilizer, but that might not be a bad idea. However, I'd have to find a way to convert to moles if I did so.

With regards to the moss: it does feel cool to the touch after at least 18 hours, so I guess it must be a bit moist, which is what I thought. I'm definitely not using the standard stuff, I just had a bunch of sphagnum naturally growing in a sundew pot so I used it. Honestly, I'm not even 100% positive it's sphagnum; I just assumed it was since it liked being soggy, got drought-stressed super easily, and holds a huge amount of water. It also looks texturally like sphagnum. But either way, it's either a local species or, more likely, it grew from spores in the substrate, which is peat moss heavy anyway.

With regards to the humidifier: I have it on a somewhat lower, but apparently still nearly as effective for plant health, setting. I also only have it on overnight. It feels nice for me--my house is rather dry, and some people already humidity when they visit, though perhaps not as heavily as I am. My assumption is that it won't cause rot as long as it doesn't condense on the floor, which happened at the super high setting but is not happening now. I think my orchid has already perked up, though, although I might be imagining it and it would be impossible to tell if the cause is humidity or fertilizer (or both, or neither).
 
  • #15
ppm is weight based, and not the number of molecules. So you put 100mg of fertilizer in 1l of water, it is approximately 100ppm TDS. Strictly, you should use (1 Kg - 100mg) of water.
Then with 30-10-10 fertilizer, 30% (w/w) is nitrogen, you'll have 30ppmN (and 10ppm of P2O5 and K2O).
 
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