Fertilizing wicking mounts - Orchid Board

Mabris · #1 10-20-2020, 03:20 PM

I have made several different types of mounts that wick from a reservoir to reduce watering requirements. Obviously, plants that don’t need drying do better in these arrangements. Right now, my plan is to top the reservoir off with RO water and mist with a fertilizer solution every week or so. This seemed likely to prevent fertilizer salt buildup better than adding a dilute fertilizer to the reservoir. I’d prefer not to have to take the whole thing to the sink t flush, but I imagine it would be necessary every few months.

Does anyone have some guidance on how best to approach this?

The picture shows some of the different ones I’ve tried out. Some, like the bulbophyllum on the left, are just a reservoir behind the cork with wicks routed over the top. There is a small psychopsis plug planted upside down onto a “kokedama” ball, which is a play-pit ball with a hole cut in the top with wicks that feed a moss exterior. The large ones are cork and wicks running up the inside and exiting through drilled holes to mounting areas. Those have mostly small species, with 9 plants on the small one and 12 on the larger. I did a similar thing with the mounted elkhorn fern.

So far the seem to be doing a good job of staying moist, though I did need to run extra wicks a couple of places after observing how they work.

Edit: forgot to add, the top of the large cork mount arrangement is a semi-hydro reservoir with a couple of plants, and that overflows into the main reservoir, so I’m kind committed to fertilizing the wicked water on that one.

estación seca · #2 10-20-2020, 04:18 PM

I hesitate giving advice to somebody who grows such amazing plants.

I don't think there is any alternative to flushing periodically to get rid of salt buildup. I couldn't predict the interval necessary, but I think you'll have to do it manually.

In constantly-moist mounts beneficial cyanobacteria eventually grow. They fix nitrogen. You might not need to fertilize as often as you would need to fertilize plants in pots with substantial drying. What happens when you cut back on fertilizing?

Mabris · #3 10-20-2020, 07:11 PM

I will have to try that out if I get some cyano growing. I did seed it with a mix of moss and fern spires I got from glassboxtropicals, so I’m interested to see how those come out.

Orchidtinkerer · #4 10-21-2020, 04:34 PM

I use wicking pots. I don't know how well moss will do long term in these though. I would imagine the moss will only last 3 months which might cause a problem. I like to find the most permanent and easiest solution possible. So moss might not be that.

What type of water do you use, rain water, tap, RO, bottled? Fertilizing the res is not for everyone, your water can't have too many salts dissolved in it as you need to add a very small amount of fertlizer (50-100ppm)

The principle of wicking pots is essentially exactly the same as semi hydro in regards to fertilizing. Fertilizing in semi hydro works so the trick is to not use a too high concentration. This is why semi hydro and wicking does not work for everyone. I personally don't think either work with tap water as it has too many salts dissolved in the water before you even add any fertilizer.
Just don't ever go over 200ppm total dissolved minerals and you should be fine. I don't flush my pots, I just water from above which flushes the pots every week a bit so with your setup my advice would be don't worry about flushing as much as having to replace the moss periodically.

Your method of spraying would work but it is more complicated as you need to work out how strong your fertilizer needs to be based on how much spraying you will do compared to how much unfertilized water the plants will wick. The point of the wick is to water your plants for you so you can leave them for a week without having to spray them. Might as well just incorporate the fertilizing in that instead of having to come along and spray them on top but if you spray once a week you just need to use a much stronger dose of lets say 500ppm.

The concern for salts accumulating on the surface is still very valid - some of my semi hydro pots used to look like it had snowed on them so many salt crystals would build up where the leca would meet air, this is a big disadvantage of leca and from my experience is the only material that draws salts to the air-exposed surface to such an extent so don't worry about it with moss, moss doesn't accumulate salts unless you really overdo it.

DirtyCoconuts · #5 10-21-2020, 06:37 PM

be warry about "flushing" any wicking string or cord...i would just plant to replace that part as it will have build up almost regardless of what you do...

that said, the plants look amazing and you might be at such low concentrations as is that there is no build up risk …?

i love mounts and have the luxury of living in a sauna...I think you are doing well, what makes you think it needs improvement?

also, rockwool cubes are my newest discovery, thanks Ray!) they stay wet for a LOOOONG time....fill a void with them, loosely, and it will stay wet for a week

Mabris · #6 11-05-2020, 04:22 PM

Thanks for the tips. I'm using RO and MSU fertilizer. i usually aim for 25-50ppm nitrogen, but for these i've been cutting whatever I've made up for my semi-hydro stuff 2-3 times with RO. I haven't yet seen any signs of nutrient deficiency, but that's what I'm most familiar with looking for. I'm not quite sure how to detect salt buildup outside of visible "crust". Do roots show characteristic damage?

I'm playing around with non-moss options. I've got a ton of the hygrolon mesh stuff. I'm exploring having some under the plant, and maybe have some moss on top where it easily replaceable and would be more aesthetic than the black wick mat. I'm also playing with a chopped of mix of moss and fern spores to try to "grow" some more moisture-retentive areas.

Ray · #7 11-06-2020, 09:25 AM

Mineral deposits occur when the solvent (water) evaporates. How the solution is delivered makes no difference whatsoever.

What is different between wicking the solution and misting it is the volume of solution delivered. Misting delivers less solution, so less solute, so there will be less buildup - but with less nutrition being delivered to the plants, as well.

What’s important to the plants is the “parts” (mass) of nutrition delivered, not the “parts per million” (concentration).

In traditional pot culture, we really have no idea how much solution the plants take up when we feed, but in S/H culture and with your wicking mounts, where there is a constant supply of solution, it has to be greater, so we compensate by decreasing the concentration.

That’s the “supply side” view, but I guess we can also look at it from the “demand side”.

For a plant to gain a pound of mass, it must incorporate about 200 pounds (~90-91 kg) of water and about 5 g of fertilizer. Let’s say we expect a plant to add a pound of weight in a 4-year period - maybe a decent guess for a mature phal. That would mean the plant - on average - must absorb about 0.024 g (24 mg) of nutrition (and about 440 g of water) per week. If 100% of what we deliver is absorbed, that suggests the “ideal solution” would be 24 mg/0.44kg=55mg/kg=55 ppm. (Note: that is true TDS, not ppm N.)

Except we know full well - but, unfortunately, cannot quantify - that the plants don’t absorb nearly that much of what we provide, as most of the solution retained in the medium is lost to evaporation. (The solids don’t evaporate and are still available for uptake as long as they’re in solution.)

So now we have to make some assumptions about percentages evaporated and absorbed.

Reminder: Our example plant requires 24 mg of fertilizer and 440 g of water (about 15 fluid ounces or 0.116 gallons) per week

If we assume 90% of the water evaporates and all of the remaining solution is absorbed (doubtful), that means we can provide that 24 mg of nutrition in 0.44/0.1=4.4 kg of water, making it a 5.5 ppm solution. If 99% evaporates, we only need a 0.55 ppm solution.