Basic Fertilization Questions
 

I bought some Miracle Gro Orchid Food, recommended by a seller, and also something I had to pick up on short notice.
I want to be sure to follow the instructions correctly. It says 'For Orchids and other indoor acid loving plants' apply 1/4 teaspoon per gallon, and apply. While it says for outdoor plants, a 1 tablespoon over soil, on the same schedule. So would an orchid kept outside, still in a typical mix such as orchid bark, receive any more than the 1/4 teaspoon? Are there different guidelines for Orchids kept in moss, or fiber?

In the long run, am I right to think I'd be better off with a strong organic mix? And one of my sellers suggests they found a great slow release mix that's better than the Miracle Gro they had been using. Are there advantages/disadvantages to slow release?

Finally, this seems tricky, how to know you have watered enough preceding the fertilizer, and not too much so that fertilizer is not absorbed, and then how to know you have thoroughly fertilized your plant, without burning? (especially with inorganic)

In agriculture people measure how much fertilizer is in a solution by the concentration of nitrogen, in parts per million (ppm.)

A lot of people think orchids do better with more frequent fertilization at a lower concentration. But not everybody has the time to mix fertilizer every time they water, so many people fertilize only once a week, or once every two weeks, or once a month. Some people like to fertilize with a low concentration at every watering (10-50 ppm N.) Others like to fertilize only once a week (50-125 ppm N), or once a month (more), with a higher concentration.

Most (not all) orchids need a lot less fertilizer than most other plants. And few orchids need much fertilizer during the cooler winter period. Some do because they grow all year.

You can learn everything you need to know on the First Rays Web site. Look at the top for Free Information, then the section on fertilizer. Ray provides a nitrogen calculator. You input the nitrogen number from your fertilizer and the desired PPM of N. The calculator tells you how much to add to water to get that number. I don't know off the top of my head what the nitrogen number is in your fertilizer.

Orchids are orchids. Inside or out doesn't matter. I use the same concentration in or out.

Bark, moss, LECA doesn't really make much difference.

So long as the fertilizer provides all the minerals and nutrients, the difference between fertilizers in how your orchids grow is minuscule compared to whether you provide the proper growing conditions. The fertilizer you bought is fine. Pay attention to learning how to provide proper temperatures, light, watering and humidity before worrying about which fertilizer to use. Note many fertilizers don't have any calcium nor magnesium. If the fertilizer lacks calcium or magnesium and the water lacks these you need to use a calcium/magnesium supplement.

Don't water with plain water first. That idea was debunked in commercial agriculture over 75 years ago. You want your plants to take up as much fertilizer as possible. Water dry orchids with your dilute liquid fertilizer. If you water with plain water the roots will soak up plain water and have little capacity for absorbing the fertilizer solution. Your fertilizer solution should be dilute enough not to harm roots, and you shouldn't rely on tricks so you can use a solution that is too concentrated. This is the big reason why people like to use a lower fertilizer concentration but more often.

Most of the larger epiphytes don't have any trouble with fertilizer concentrations of nitrogen around 150ppm. Cloud forest orchids and slipper orchids prefer much less than this. If you go to the Sunset Valley Orchids cultural information page, Fred Clarke tells you how he applies MSU fertilizer to his plants. If your Miracle Gro has a different nitrogen number, you can use Ray's calculator to determine how to mix your fertilizer to get numbers similar to what Fred uses.

Could you clarify where Ray's calculator is?

Fertilizer PPM Calculator

Or, if you just want to be in the ballpark, use the flowing estimates:

For 25 ppm N, 2/%N = teaspoons/gal, or 2.3/%N = ml/L

So if I want a 100 ppm N solution of MSU RO @ 13.2% N, that would be 2/13.2=0.1515. Multiplied by 4 = 0.6 teaspoon (I’d just round down to 1/2), or if you want metric measures, 2.3/13.2=0.1742 x 4 = 0.7 ml/L

It seems like slow release fertilizer would just wash out of an open bark medium long before it had a chance to release its nutrients.
I'm not sure what a "strong organic mix" would be, but you don't want to add anything that would clog up the air spaces in your potting medium.
The Miracle Grow Orchid food (and there are others) is formulated to meet the needs of the plants. I'd use the 1/4 tsp per gallon, weekly. I doubt you'll see any signs of deficiencies in your plants, but if you do you can adjust accordingly at that time.
Thanks ES and Ray for the more detailed explanations, but just following instructions on the orchid food container has actually worked pretty well for me!

What about the amount of application? Using the solution instead of water in that watering including soaking method, or just add enough by spraying to wet the top of the soil?

I am a proponent of flooding the potting medium at each watering, as it flushes, saturates, and aerates all in one step. Over winter, when the plants are indoors, I mostly use a heavy spray on the media surface until drainage starts, which is admittedly less thorough.

We really don't know how much of what we apply is actually absorbed, because we don't know the retention of all potting media, we don't know how well solutions are spread around the pot as the water evaporates, and we don't know the contact area of the root system in relation to those. My recommendations are just the culmination of years of growing and observation, using the techniques I employ.

I did a calculation (AKA - "sheer folly") based upon the chemical reactions that fix carbon and the resulting nitrogen and water requirements, based upon an assumption that a plant gains one pound of mass in four years (Phals, maybe?), and if it was 100% absorbed, we could water 1 pint (16 fluid ounces, or about 570 ml) a week using a 55 ppm solution (assuming about 50 of that was N).

I would water thoroughly each time. Just wetting the surface means dissolved minerals dry on the upper part of the medium.
This shows as powdery white efflorescence, which may damage roots.

Thorough running-out-of-the-pot watering has the additional benefit of pulling fresh air into the root zone, along with flushing out any buildup of fertilizer salts and other crud,

Thanks to all for your advice! So in this case, how do you flood the medium? Do you soak the whole pot in a plastic tub, or something along those lines, with the less concentrated solution for fertilizing with every watering? If not, what constitutes flooding?

I would think that at a certain point wood chips, for example, would be totally saturated with the fertilizer solution, which I would think wouldn't harm the plant. I would also imagine, when flooding, then the roots can also become saturated, which would be safer at lower concentration. If I am correct, then would this not make a very thorough flooding with lower strength fertilizer with each watering, more efficient for growth as well as safer for the plant? Just speculating! :)

I don’t “soak” my plants by submerging the pots, I use a hose with a “water breaker” or “rain head” on the end, so the flow resembles heavy, air-entraining rainfall, and let it get fully flowing through the medium. I think that is probably the best way to do so.

Water is, by far, the most important factor to growth, so I think you are correct that the best thing you can do is find a way, through selection of potting medium and container, to be able to water heavily and often, and yes, with a tiny bit of fertilizer.

Adequate water at the root system is a trigger for the plant to open its stomata for gas exchange, allowing more carbon dioxide intake, which leads to faster carbon fixation - growth. If you grow in a medium that must dry out to avoid suffocating the roots, you are forcing the cycling of that process on and off, which must slow things down.

Granted, this is a very generalized and simplistic description of the “base process”, as plants handle such activity differently, but the concepts are still applicable.

Apologies, I mistakenly added an unnecessary post, and not sure how to delete it! :)

---------- Post added at 01:24 AM ---------- Previous post was at 01:00 AM ----------

Thank you for the enlightenment! How do you apply fertilizer when watering with a hose? Do you use the hose attachment that holds and dispenses fertilizer automatically as you water, along with the rain head you mentioned? (maybe both features in one attachment?) and if so what concentration do you place in the attachment? (If it's not too much trouble could you tell me the name of the attachment you use?)

How do you water very small plants, like in 2-3" pots, just shower over them? Also, when you say tiny amounts of fertilizer, is that the 25-50ppm that Estación Seca described?

Again, I truly appreciate all the tips. And sorry for the barrage of questions, I really want to get the right practices down! And you seem to have the right answers lol :thanx:

btw will check your website for answers too! :)

There are many ways to "skin that cat". When I grew in a greenhouse, I used a metering pump the injected a liquid fertilizer concentrate into the water passing through the hose. I used a Dramm Water Breaker to make it "rain".

Now that I have retired and downsized, and have no greenhouse, when the plants are out on my deck, I use an Ortho Dial-and-Spray hose-end sprayer to add the fertilizer and other additives.

When they are indoors over the winter I use a battery-powered backpack sprayer that also has a wheeled dolly so I can just roll it around. I put everything in that and adjust it for a coarse spray.Again, it varies with the circumstances.

When the fertilizer was injected with the metering pump in the greenhouse, I used 25 ppm N and watered 3-4 times a week. In summer outdoors, here in NC, I have to water frequently, but being more of a hassle to use the hose-end sprayer, I feed weekly at 100 ppm N.

I generally recommend that you think about the frequency of feeding, then sum up the concentrations applied, making the total somewhere in between 75 and 125 ppm N.

Under my "equal abuse" policy, all plants are treated the same.

"Equal abuse policy." That's the policy I follow here as well. Well-stated. :biggrin:

For a small collection, a 2 gallon pump sprayer is handy. You can fill with your fertilizer solution (or plain wanter) and easily carry it around. that is my "indoor hose" and also how I used to fertilize outside (long after my collection could be considered "small".)

Any water-soluble fertilizer that provides N, P, and K is fine. If it also provides Ca, Mg, and trace elements, even better (if your water supply does not have much of these). More frequent but dilute applications seems better than infrequent strong applications.

An orchid does not really care whether nitrate-N, ammonia-N, K, or P comes from an organic fertilizer, or a fertilizer that might be considered "inorganic". Also, most orchids don't need much fertilizer, as others have said. Wild orchids living in trees get their nutrients from animal wastes, plant exudates, plant and animal debris trapped in the orchid's roots, really anything that comes along. Some of the nitrogen actually comes from rainfall itself.

Slow-release can be OK, and I know people that have used it. The fertilizer is in small spherical capsules called"prills". If you go this route, shop carefully for types meant to be very slow release, for epiphytes. A friend that used slow release has cautioned that some cheaper slow release fertilizers can "dump" their remaining fertilizer all at once under certain conditions (not desirable). I don't recall the conditions that causes that dumping, but frankly, it was a reason I have stayed away from slow-release fertilizers for orchids.

I use slow-release ferilizer in addition to my regular regimen for particularly rapid-growing, "hungry" types... mostly Cymbidiums and Catasetinae, in the spring. Contrary to usual perception, they don't leach their payload so much in response to water as response to temperature. So a hot spell can produce a burst. Which is OK for those fast-growing types, they are likely to also increase their growth in hot weather. But it's likely to be too much for most orchids. In general, it's better to under-fertilize than over-fertilize. Too little and the plant may not grow to its full potential. Too much and you can burn leaves and roots, damage the plant.

I use just as Roberta says… plants like Cymbs, Ctsm, that can just drink it down with the rapid growth cycle. For most… weak and infrequently.

I'm curious, why can't you use a metering pump outdoors? Forgive me, I am not familiar with their usage.

So is the 75-125 ppm N the concentration in the dial sprayer, and not what comes out of the hose? So this doesn't to some degree diminish the advantage of watering frequently at very low concentration?

Also, forgive these two basic questions... When do you know you have watered thoroughly enough, and do you wait until substrate is nearly, or fully dry (depending on species?) to water?

Finally, what is a good way to acquire the kind of knowledge many of you have of species. I know it is recommended to research the various habitats. But are there any particular books, or websites, like Orchid Wiz, to study for this knowledge? :thanx:

---------- Post added at 10:53 PM ---------- Previous post was at 10:46 PM ----------

I have a 3 gallon pump sprayer for my Bonsai. I already have 7 Orchids, got a bit carried away lol, but they are doing well, luckily. So I imagine another 2 or 3 gallon sprayer would work for awhile?

Just pertaining to the species orchid question, an old but good source are the Baker culture sheets: Orchid Culture -- Charles and Margaret Baker
I don't have Orchid Wiz, but I have heard the Baker sheets may be incorporated into that database.

You certainly can use them outdoors, and I have been considering that, considering I would use the solution for my orchids, bedding plants, fruits, vegetables, and herbs. They aren’t cheap, so getting one to fertigate a small number of orchids simply may not be worth it. The particular sprayer I have has a 1-quart feed tank and can be adjusted to a large range of dilution rates. I typically use 1 oz/gal, meaning the tank can have 32 gallons of capacity. Then I just add the proper amount of powder to make each gallon dispensed be at 100 ppm N, when diluted one ounce per gallon, fill it with water and go.

In my opinion, while the dilute/frequent scheme is likely the best, it is certainly not the only way to feed. Personally, I try to avoid going longer than a week or maybe two, between feedings, but monthly is not unheard of. I suspect that the plant will get more fertilizer if fed 4 times a week @ 25 ppm N than if fed once a week @ 100 ppm N and just watered 3 other times, but is that a significant difference in such slow-growing plants? I try to never let my plants dry out. I water heavily until water is rapidly draining out of the pot. Google is your friend! Read everything you can get your hands on, in print and online.Sure. Why not?

I found that a 2 gal pump sprayer was completely adequate for quite a few orchids... before I bought my house, when I first got into orchids, I lived in a condo and the spare bedroom became my "greenhouse" http://orchidcentral.org/GrowingAreas/indoor.jpg .
I just watered these until the water ran out of the pot. The bins under the plants caught the water. its evaporatuin raised the humidity a bit. I only had to clean out the bins every 6 months or so when the algae got too ugly.

Wow that setup looks awesome! Well for my orchids in wood chips, water starts flowing through in just a few moments. Do I wait until it's at maximum flow, no longer increasing? That's my theory haha.

So do you treat a plant in moss any differently? I imagine you would water less often. Though, would it be okay to use the same concentration as with orchid bark?

So can you water too much at once, in a single watering; can that burn the roots? Either with low concentration, or higher?

:thanx:

Considering you’re flushing the medium at the same time, I think your “theory” is valid.

In my opinion, the same principles apply, but keep in mind that heavy, top-down watering of sphagnum will compress it, so it will need to be replaced more often.

As far as the concentration question is concerned, I think you need to consider “exposure time” in your thinking.

Roots can only absorb solutions while in direct contact with them. For a vanda grown bare root in a basket, that occurs only when the plant is watered. For a plant in coarse bark, it is longer, because the saturated bark can still deliver some solution to the roots in contact with it for a bit. In sphagnum, the root contact area is greater and it holds liquids longer. Semi-hydro culture provides constant contact, but less contact area, due to the coarse medium.

Try the analogy of a shower, where the hot water component is the “fertilizer” - no matter what “dilution” factor (that is, cold to hot), and no matter how long you’re in the shower, your exposure is constant, and once you turn off the water and you dry off, the exposure ends until the next shower.

During your exposure to the shower, your skin has had an opportunity to absorb some water, and the longer you’re exposed, the more that will be.

We know that velamen is like a sponge, trapping solutions for the plant to take up at its own pace, but we don’t really know how rapidly the liquid is actually taken into the vascular system from the velamen. Here, I think the shower analogy applies again - if warm (dilute), you can stay in it all day, but if hot (concentrated), you’ll get burned almost immediately.

Orchidwiz includes more than 4700 Baker sheets (the entire opus, including some that were scanned from hard copy). It's my go-to source along with orchidspecies.com . Together, I end up with an encyclopedia of species information.

If you want a magnificent set of books stuffed with species info and photos on the smaller species, consider A Compendium of Miniature Orchid Species by Mary E. Gerritsen and Ron Parsons

Thanks for the recommendations! I forgot to ask a basic question. With the dilute fertilizer with every watering, I am adding 1/8 tsp per gallon for 50 ppm, of Miracle Gro Orchid Food. Is it okay to use a very heaping spoonful?? ;)

And if that's okay, can I mash it down and heap it more?! :)

It's like cooking, or performing chemistry. Use a level measuring spoonful. Level it with a butter knife if you can't get it even on the opening to the container. Don't mash it down.

If you use a heaping spoonful or mash it down you will make a higher concentration of solution than you want.

More is not better. Think of the nitrogen content as “calories” in your own diet: too few and you won’t be strong enough, the correct amount and you’ll be healthy, and with excess, you’ll become fat, flabby, and disease prone.

As an aside, when the Northeast Georgia Orchid Society closed it's doors (not enough people left in the club that could help run things :( ), we took the remaining treasury, and donated it to the State Botanical Garden of Georgia, specifically so they could purchase OrchidWiz.

I have my diluted fertilizer in a spray bottle. In addition to bi weekly drench fertilizing, I spray fertilizer water on the base of the orchids every other day. Not enough water to rot roots or wet the pot but enugh for it to be taken up by some parts of orchid roots.

Why so much fertilizer? Unless it is VERY dilute (like maybe 1/8 strength) you're overdoing it.
And if you're just dampening the surface (so that the water evaporates quickly) the solids will, over time, become more concentrated. I hope you are flushing well with clear water (no fertilizer) every couple of weeks, that will mitigate the salt buldup.