Dendrobium kingianum. What is low nitrogen fertilizer?

[sunfire]

I have a Dendrobium kingianum that I received a couple years ago as a small cane/keiki. In that time I have certainly abused it but instead of dying, it produced several keikis. I am more seriously focused on caring for this plant and it’s offshoots now and have read that it needs a “low nitrogen” fertilizer to improve growth and reduce keiki formation.

So my question is: what exactly qualifies as a low N fertilizer? I mixed up a “K-lyte“ knockoff using the calculator at firstrays.com (approx 13-2-2-14-3) and have been using this at 25-50 ppm on my phals in SH. Does 25ppm N count as “low N” or does the N need to be a lower percentage in the fertilizer, like a “Bloom Booster” fertilizer with either high P or high K compared to N?

Also, theoretical question regarding the K-lyte formula in SH. If flushing the pot “refreshes” the chemistry, is going with such a low P and K formula necessary? Any excess P and K “should” be washed out each time. Just pondering… thanks!

[estación seca]

Your current fertilizer regime should be fine. Stop fertilizing in late summer, and resume after buds are well advanced. Cool winter nights are also important in blooming this plant, 55 F / 12C for 6 weeks or more. It prefers a lot of winter light.

Your tap water may contain minerals. Regular thorough plain watering is needed to reduce mineral buildup

[sunfire]

Thank you! Glad it know that 25-50ppm N regardless of P and K counts as low N.

I have been using distilled and RO water (because my tap is softened). Wouldn’t RO/distilled flushes wash out any excess P or K in S/H set up if I were to instead just use a “balanced” fertilizer?

Originally Posted by estación seca

Your current fertilizer regime should be fine. Stop fertilizing in late summer, and resume after buds are well advanced. Cool winter nights are also important in blooming this plant, 55 F / 12C for 6 weeks or more. It prefers a lot of winter light.

Your tap water may contain minerals. Regular thorough plain watering is needed to reduce mineral buildup

[estación seca]

Sorry, I don't understand your last question.

Forgive me for going back to basics; you may know this. To do S/H properly, the pot should be filled to the rim at every watering, displacing all the air, then be allowed to drain. Some people do this twice at each watering. This reduces mineral buildup. If just a little solution is added at each watering, only enough to top up the reservoir, harmful mineral buildup occurs surprisingly rapidly. Displacing and replacing all the air is an important benefit of S/H.

In S/H, if watering properly every time, with water containing any minerals or mineral compounds, some salts will eventually build up in the LECA as the solution evaporates, and the LECA dries. But if low concentrations are used and the minerals are quite soluble it would have very little effect. Some people growing in S/H water every time with a very low concentration fertilizer solution, and others use higher concentrations of fertilizer at longer intervals with plain water in between. Both approaches work; many people think the feeding at every watering approach is somewhat better.

Whichever approach is used, most people will occasionally water with plain water to rinse out as much of the retained minerals as possible.

Using RO or distilled water and low concentrations of fertilizer, your plants are probably not getting enough calcium nor magnesium. Most fertilizers lack these elements because they cause solubility problems when mixed with other nutrients. Use a separate calcium-magnesium supplement regularly, but not at the same time as your fertilizer, because of the solubility issues.

If you have access to a hose bibb outside you might be able to get untreated tap water to mix with your reverse osmosis water, potentially providing calcium and magnesium. Outdoor hose bibbs are rarely plumbed into water softeners, because the sodium used is also bad for outdoor plants.

[Ray]

“N” refers to nitrogen. The P, K, and any other mineral in the formula is totally irrelevant when discussing N.

Fertilizer formula is irrelevant. It tells you the concentration of the ingredients in weight percent. A 20-10-10 has double the concentration of a 10-5-5, so you simply need to use half as much per feeding to give the plant the same nutrition.

Likewise, ppm N merely specifies the concentration of nitrogen you are supplying in your solution.

In addition to concentration, you need to consider frequency of application and extent of exposure in your thinking.

We have no idea how much of what we apply is actually absorbed by the plant, but can reasonably assume it is the same every time we feed - assuming it’s done the same each time. Based upon that, if you feed twice a week, you’re giving the plant double the mass of nitrogen that you would if you fed once a week. AND, if you apply a 50 ppm N solution, the plant can reasonably be expected to absorb twice as much nitrogen as it would if fed a 25 ppm N solution at the same frequency.

Then there’s the exposure.

If you feed a vanda growing bare root in a basket, the time it has to capture nutrients is only as long as you’re wetting the roots. At the other end of the spectrum is hydroponic growing, where the roots are always wetted by the nutrient solution.

If you want the vanda and hydro-grown plant to get the same mass of nitrogen, it is going to need a much more concentrated solution, applied frequently.

As to your flushing with pure water question, recognize that plants can only take up nutrients in solution, so by doing thorough flushes, you’re replacing a nutrient solution with one containing no nutrients, as they all have been removed. (I’m disregarding the nutrients accumulated in the medium, as there’s not much you can do about that, and it is never completely removed.)

For plants needing a “winter rest”, stop feeding.

[sunfire]

Thank you for taking the time to help me out here!

I am using a fertilizer that I mixed up myself using the "K-Lyte knockoff calculator" at the firstrays.com site. I liked the write up and have a gram scale and the ingredients so I decided to DIY. By my calculations my mix has approximately

12% N
2% P
2% K
13% Ca
3% Mg

mixed into RO water with a TDS of about 20 and a pH of 6. So I am not too worried about the lack of Ca/Mg in my RO using this fert.

My question was more theoretical- if I am using the SH methods like you outlined above with a full flush of solution (plain RO water or RO water plus the above fertilizer) at appropriate intervals, is mixing up my own low P and K fertilizer necessary vs just using any other fertilizer at a concentration of N between 25-50ppm since the plain water flushes presumably will clear out excesses that are left over regardless.

Theoretically, doing appropriate full frequent flushing there should be no excess of any ions to accumulate. But... now that I am writing this out, presuming LECA has a high CEC perhaps this is okay, but could lead to a deficiency in P and other anions? The chemistry is complex and I am sure I am just missing something here.

I think this is what started my question "what is a low N fertilizer". Is it the NPK ratios (N>>P/K like I am using) or is it the overall concentration (ppm) of N (and I think you said the answer is the latter). So if I do full flushes, could I theoretically be under dosing P and/or K using this low P/K mix I made.

Originally Posted by estación seca

Sorry, I don't understand your last question.

Forgive me for going back to basics; you may know this. To do S/H properly, the pot should be filled to the rim at every watering, displacing all the air, then be allowed to drain. Some people do this twice at each watering. This reduces mineral buildup. If just a little solution is added at each watering, only enough to top up the reservoir, harmful mineral buildup occurs surprisingly rapidly. Displacing and replacing all the air is an important benefit of S/H.

In S/H, if watering properly every time, with water containing any minerals or mineral compounds, some salts will eventually build up in the LECA as the solution evaporates, and the LECA dries. But if low concentrations are used and the minerals are quite soluble it would have very little effect. Some people growing in S/H water every time with a very low concentration fertilizer solution, and others use higher concentrations of fertilizer at longer intervals with plain water in between. Both approaches work; many people think the feeding at every watering approach is somewhat better.

Whichever approach is used, most people will occasionally water with plain water to rinse out as much of the retained minerals as possible.

Using RO or distilled water and low concentrations of fertilizer, your plants are probably not getting enough calcium nor magnesium. Most fertilizers lack these elements because they cause solubility problems when mixed with other nutrients. Use a separate calcium-magnesium supplement regularly, but not at the same time as your fertilizer, because of the solubility issues.

If you have access to a hose bibb outside you might be able to get untreated tap water to mix with your reverse osmosis water, potentially providing calcium and magnesium. Outdoor hose bibbs are rarely plumbed into water softeners, because the sodium used is also bad for outdoor plants.

---------- Post added at 01:58 PM ---------- Previous post was at 01:49 PM ----------

Thank you for the information. It is great to interact with you here. I think I have read all of the articles on your firstrays.com site a couple of times. I have really enjoyed them! I am hoping that I can use the SH methods you developed to become a better orchid grower. FWIW, I do full flushes and not top offs. The best thing I find about this method is there is no soaking of media (other than to start off). I think that is where my problems were with bark medias. I just don't have the time to soak a pot and when I would water it after it was dry, the water would run straight through the dry bark media and I would still have a dry (very dry) plant in the end. I have softened water so running tap water through a plant in the sink is not an option for me.

I wrote another probably too long and very confused reply above circling around my limited knowledge of soil chemistry. Have you ever had any concern about P or trace mineral deficiencies using K-Lyte? I presume using this formula you do not also supplement with Cal/Mag?

Thank you!

Originally Posted by Ray

“N” refers to nitrogen. The P, K, and any other mineral in the formula is totally irrelevant when discussing N.

Fertilizer formula is irrelevant. It tells you the concentration of the ingredients in weight percent. A 20-10-10 has double the concentration of a 10-5-5, so you simply need to use half as much per feeding to give the plant the same nutrition.

Likewise, ppm N merely specifies the concentration of nitrogen you are supplying in your solution.

In addition to concentration, you need to consider frequency of application and extent of exposure in your thinking.

We have no idea how much of what we apply is actually absorbed by the plant, but can reasonably assume it is the same every time we feed - assuming it’s done the same each time. Based upon that, if you feed twice a week, you’re giving the plant double the mass of nitrogen that you would if you fed once a week. AND, if you apply a 50 ppm N solution, the plant can reasonably be expected to absorb twice as much nitrogen as it would if fed a 25 ppm N solution at the same frequency.

Then there’s the exposure.

If you feed a vanda growing bare root in a basket, the time it has to capture nutrients is only as long as you’re wetting the roots. At the other end of the spectrum is hydroponic growing, where the roots are always wetted by the nutrient solution.

If you want the vanda and hydro-grown plant to get the same mass of nitrogen, it is going to need a much more concentrated solution, applied frequently.

As to your flushing with pure water question, recognize that plants can only take up nutrients in solution, so by doing thorough flushes, you’re replacing a nutrient solution with one containing no nutrients, as they all have been removed. (I’m disregarding the nutrients accumulated in the medium, as there’s not much you can do about that, and it is never completely removed.)

For plants needing a “winter rest”, stop feeding.

[estación seca]

"Low-nitrogen fertilizer" isn't a scientific term. My observation has been people usually use it to refer to a fertilizer with a lower N percentage than other fertilizers.

The numbers were formulated based on studies of element composition in dried plant material, with the guess that supplying elements in those proportions would lead to good plant growth. I don't know whether that's been studied enough to say it's true.

As Ray mentioned, how the fertilizer is diluted has more to do with the N concentration.

And backing up - fertilizer is the least important aspect of orchid culture. Pay more attention to proper temperatures, humidity and light.

I will throw another idea in here - many commercial growers use much more nitrogen when fertilizing than standard recommendations suggest. Plants in ideal growing conditions will grow faster than plants in suboptimal growing conditions, like in most homes. It stands to reason they could use more nitrogen.