Feeding Potless Vanda

[K-Sci]

This question is more about technique than one's preferred nutrient, but I realize that one can't be discussed without the other.

Vanda are often described as heavy feeders. Is this because they require more NP&K, or is it because they often don't have media to absorb it for later release?

How do you feed your potless Vanda?

The orchid that inspired my question is shown in the attached photo. Note that the top leaves are not quite as large as the lower ones.

K-Sci

[Ray]

In my experience, 25 ppm N, applied daily, soaking the roots thoroughly each time, seemed to work well in a greenhouse in PA.

[K-Sci]

Originally Posted by Ray

In my experience, 25 ppm N, applied daily, soaking the roots thoroughly each time, seemed to work well in a greenhouse in PA.

How do you "soak" a root mass as large as the one in my photo? At best I can pour the mixture over the roots, but that's not what I would call a soaking.

How does one know the mixture is 25ppm?

Thanks in advance for your reply.

[estación seca]

In his older book on Vanda growing (which you can still find for sale) Martin Motes reported he watered his bare-root Vandas once every morning of the year, and often a second time in early afternoon during hot parts of summer. In recent videos he says he still waters this way. In a video you can find easily on YouTube, he went down the line of bare-root plants hanging on wires with a hose and a water wand, thoroughly wetting all the roots. Then he went back to the start of the row and did it again, to ensure the roots were completely wet, and changed from white to green.

People living in houses can duplicate this by soaking the roots in a bucket until they turn dark green. My experience has been they don't mind overnight soaks in the least; in fact, this is a good idea in a lower-humidity home.

In the book he said he fertilizes every 5th watering, using a fertilizer injector for the hose. The solution delivered to the Vandas was 1 Tablespoon (15ml) of 20-20-20 with micronutrients per gallon (3.78 liters) of water.

He has since said he switched to a MSU formulation rather than a 20-20-20 formulation. I've looked but I can't find him saying whether he still uses 1 Tablespoon per gallon, but I can assure you that amount makes Vandas grow fast.

That is a lot more than other people recommend, but Motes grows Vandas for a living.

In the book Motes wrote a properly fertilized Vanda has a zone of lighter green at the very base of the newest emerging leaf that is about a centimeter wide. If the lighter green band is not this wide, the plant needs more fertilizer. If the lighter green band is wider, the plant is being overfertilized.

I have written this here before and OB members have not been able to understand what I meant. I think this might be because they don't fertilize much, and there is no light green band. I have been told here Vandas might make 2-3 new leaves per year. When properly fertilized they grow much faster than most people would imagine.

[yug]

Dissolve the fertilizer in water at the right concentration, pour into a spray bottle, and spritz away until soaked.
(is that what you are asking?)

[K-Sci]

Originally Posted by yug

Dissolve the fertilizer in water at the right concentration, pour into a spray bottle, and spritz away until soaked.
(is that what you are asking?)

Pretty much. That's what I've been doing, but noticed that the new leaves on my Vanda were shorter than the earlier ones, suggesting that I need to increase the frequency or concentration. I've been doing what you described every 2 weeks with Miracid (now Miracle Grow for Acid Loving Plants) at 1/4 tsp/g. I rotate the plant to get all sides. It is a slow process, and I suspect that commercial growers have a less time consuming approach.

I live in rural Mississippi where there are no nearby orchid greenhouses to ask. The question came up, in part, because I just bought another Vanda. Based on the level of interest, it's a very good question.

[Ray]

Originally Posted by K-Sci

How do you "soak" a root mass as large as the one in my photo? At best I can pour the mixture over the roots, but that's not what I would call a soaking.

I always water with a water breaker on the hose end. I helps simulate a heavy rain, watering and aerating. I guess I should have used the term “drench” rather than “soak” which implies dunking.

How does one know the mixture is 25ppm?

The more precise method is to weigh the fertilizer in the right ratio for the fertilizer formula.

1 ppm is 1mg per kg, or 3.785 mg/gallon, so a 25 ppm N solution will contain 3.785 x 25 = 94.625 mg N (95 is close enough), so 95/(nitrogen percentage) mg of fertilizer.

If using a 20-20-20, therefore, you’d need 95/0.20=475 mg fertilizer per gallon.

The much easier method, (and close enough), is to divide 2 by the %N (as a whole number), giving you the teaspoons/gallon.

The 20-20-20, therefore, would require 2/20=1/10 teaspoon/gallon for a 25 ppm N solution.

As that would be a pain to measure, I recommend making a concentrate. Let’s say you want to dispense a tablespoon of liquid fertilizer concentrate to make a gallon of usable solution. Each tablespoon would have to contain that 1/10 teaspoon of powder, and as there are 256 tablespoons in a gallon, you simply dissolve 256/10 (either 25 or 26 are fine) teaspoons of powder in a gallon, the mix up your final solution using a tablespoon of that.

[Shadeflower]

good advice Ray,
if I may I will just address the question of how to know how much 25 N is.
To me the main Nutrients that make up a fertilizer are NPK and most fertilizers are are an equal ratio. The other main Nutrient a fertilizer should have is Calcium and then all the other micronutrients like magnesium, boron, iron, manganese, sulfur, mobyldium, copper, etc,
so as a rough guide I like to think that N takes up 20% of a fertilizer, P another 20%, K another 20%, Ca another 20% and the rest takes up the remaining 20%.

So multiply 25ppm N by 5 (20% x 5 =100%) and the ppm you should be aiming for will be roughly 125ppm which should roughly have 25 N but this is an overly simplified version and some fertilizers contain very little K so might contain more N overall. It's just to help out that a well balanced fertilizer at 125ppm will contain roughly 25ppm N because that is 20% of it.

That is actually on the lower end of fertilizing so that tells us that Vanda's do not need much more fertilizer than other orchids. They might benefit from a little higher dose while they are actively growing (up to 250ppm).

That is if they are let to soak in the water and fertilizer.

If water is poured over the roots fast and dries off fast then the plant hasn't got as much time to absorb the nutrients so the advice of feeding a higher concentration comes into play but I have never tried it, I much prefer to let mine soak in low concentrations.

I have often been pointed out by others that Vanda's do need higher doses of fertilizer but I have seen no evidence of that and am with Ray on the 25 ppm N being enough (as long as the plant can absorb the nutrients over time)

What I have seen is that Vanda's are quite heavy drinkers. As such they drink more than lets say an angraecum.
Both have roots that are just as sensitive to fertilizer burns. You often see fertilizer burns on roots. They turn into brown patches on roots. So should you feed a vanda more than an agraecum? To me no, only a little more during active growth. The reason for this is simple.

The angraecum might only drink 100 ml of water in a year so it will only absorb whatever fertilizer was in 100ml of water.

A vanda will drink far more than this. I haven't got extensive experience with vanda's, the size makes a huge difference and the climate and humidity level but for argument sake lets take an average of 10 liters per year for a vanda. That vanda will be absorbing 100 times more nutrients than the angreacum only drinking 100ml per year.

So the heavy feeders, feeding even more on top in the 10 liters the vanda will drink in a year I believe they are over-feeding which doesn't do the orchid any good and this shows with brown fertilizer spots on roots.

As a sidenote: stunted orchid leaves have nothing to do with underfertilizing. That is a sign of stress and can even be caused by roots performing badly in the pot.
Things that cause stress include, wrong temperatures, day or night, overfertilizing, not enough healthy roots/ not watering the orchid enough or the substrate doesn't dry fast enough. Too little light might play a role but most often transport stress is the most likely reason for smaller leaves. Disease can cause stress and many other factors. Feeding too little, would not result in stress unless the orchid was severely lacking Nutrients but this would show as a deficiency far sooner than as stunted leaves growing. I don't worry about stunted leaves as much as I used to and have come to accept that most new orchids that have gone through transport stress will display some stunted growth as a result and I shouldn't think to change my growing methods just because the orchid did suffer stress which we know about. If it happens randomly out of the blue then that would be different.

It is extremely hard to learn how much to feed an orchid that is going through a stressful transition period so it helps to have a ppm meter so one doesn't have to guess on an orchid that will develop stunted growth whether you feed it perfectly or not. Feeding too little might reduce the orchid size a bit or produce a bit of yellowing on leaf edges but it is nothing that can't be rectified the following year, feeding too much does much bigger damage that is permanent and takes an orchid years to recover from so I know people always mention it but it is hard to understand how easy it is to damage roots and how long the orchid has to live with that damage for.

I think where people encounter problems is not feeding regularly. I will use a comparrison as an example. Lets say you have a guy called Rob who likes to drink a glass of squash every day. He likes his squahs, it is refreshing and doesn't burn his throat, he adds the right dose to his glass ever day and it refreshes him.
No loets say Rob got a bit lazy and thought, I know w better way, instead of adding squahs to my glass of water every day I will add all the squash only on a sunday. This saves me adding squahs to my glass every day and I will still absorb just as much squahs at the end of the week. So Rob drinks a glass of water every day for 6 days and on the last day he washes it down with 7 doses of squash which he suddenly realizes is far too strong, it's super concentrated, burns his tongue and leaves a horrible taste in his mouth for the rest of the day.
If you compare that to a vanda, the vanda will much prefer to receive the right dose of fertilizer every time it gets watered over no fertilizer for a lot of waterings and then far too much to make up for the lack in nutrients all week. So learn from Rob and add squash to your glass every time.

[Ray]

Originally Posted by Shadeflower

To me the main Nutrients that make up a fertilizer are NPK and most fertilizers are are an equal ratio. The other main Nutrient a fertilizer should have is Calcium and then all the other micronutrients like magnesium, boron, iron, manganese, sulfur, mobyldium, copper, etc,

That is precisely why fertilizers are so frequently debated!

What you state is absolutely correct, but how do we know what the plant needs? Correct answer: we really don't.

To my mind, tissue analysis comes the closest, but we have to recognize that tells us what the plant has been receiving, not what it needs. If it was a reliable indicator, my tissue analysis suggests I need a lot of cholesterol!

However, tissue analyses of established colonies of wild plants ought to give us at least an inkling of what they have evolved to survive with, even if its not "ideal".

Generally speaking, about 90% of a plant is water. About 9% is C, O, H, and N. About 0.9% is P, K, Ca, Mg & S, with everything else combined to about 0.1%.

By far, the most important fertilizer ingredient is N, so if you provide sufficient N and the other ingredients are neither deficient nor so great that they antagonize the uptake of another, you should be OK. A plant is going to use what it needs, and no more. deficiencies slow growth, excesses are wasted.

[Clawhammer]

Great looking plant.

As long as you are applying some kind of ferts on a somewhat regular basis ferts will not be your problem. Orchids need very little and are quite adept at snatching nutrient ions out of water even when they are present in small quantities. i don't believe your observation about the leaves indicates an underlying issue.