Techniques for fertilizing three different genera of orchids

laura_fl(8.5)October 3, 2010

Hello. I am new to orchid gardening and have a question for the knowledgeable people on this forum. Any advice would be appreciated. :)

I have been reading about orchid fertilizing and am confused on a few points. I seem to find more information about what to use when fertilizing orchids rather than how to actually apply the fertilizer. I plan to use a 20-20-20 powder fertilizer for orchids that you dissolve in water.


- I have read you should water the plant first. Immediately before?

- Do you soak the pot in a dish with the dissolved fertilizer or just pour it on? If soaking for how long?

- Is it important to apply the fertilizer just to the roots or also to the leaves? If it does get on the leaves do you need to clean them before they dry?

The orchids I have are:

- A recently purchased small Vanda in a small black plastic basket with bare roots. I have anchored this basket to a wood fence on my deck with metal hooks.

- A Dendrobium moschatum orchid in potting mix I just repotted into an 8" slotted terra cotta pot placed next to the fence on my deck outside. The plant is four feet tall and I have had it for years. When I transplanted it I found it had an amazing number of incredibly tightly packed roots. The few times I have fertilized it I have just poured fertilizer over the top of the potting mix after watering it.

- And the final orchid I have is a Phalaenopsis that has four nice healthy leaves and almost no roots. I just repotted it from rotten sphagnum moss it came in (why it lost all its roots) into orchid potting mix in a slotted terra cotta pot on the dresser in my bedroom. It seems water just runs right out from the potting mix on this one so I am not sure how effective pouring fertilizer over this

Sorry for the length of this post.

Thanks for your help and cheers!

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richardol(Santa Royale CA)

Here is what I think. There are other opinions so read and decide for yourself.

20-20-20 is good, I use whatever even low number is least expensive and mix it between 1/2 and 1/4 of what the directions say.

Dry roots are slow to absorb so that is why watering ahead is good. I water, then go back around with the fert in a pump sprayer and spray any visible roots and the medium. I don't spray any leaves on purpose. Any time on the morning you water would be fine.

Orchids are slow-growing plants and don't need much. Some are considered "heavy feeders" but that is relative, nothing like what a fast growing tomato plant, for example, would need.

    Bookmark   October 3, 2010 at 1:05PM
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1. For the average, non-commercial / non-expert grower, watering your orchids before you fertilize is an excellent idea, and while it's not a vital piece of care for your plants, it's something you should strive to do. And yes, water heavily and thoroughly immediately before feeding. Run plenty of water through the pot, so that several volumes of water have run out through the drainage holes. Give the mix and the roots plenty of time to get soaked and absorb the moisture. Then feed.

The justification? Well, orchid roots are very sensitive to environmental conditions in general, and they are especially sensitive to salts and minerals (resulting from fertilizer) that tend to build up in your pots over time. As richardol stated, orchids just aren't heavy feeders in comparison to many other plants, and even though you are advised to feed at 1/4 to 1/2 strength of whatever the fertilizer directions say, your plant is still not going to be able to absorb all of the food. So, it will build up and could threaten your orchid. Watering heavily and thoroughly before fertilizing helps to flush out any salts remaining in the pot. And, it can help act as a bit of a buffer if you happen to mix up a batch of fertilizer that's a bit too strong, since whatever you add to the pot will now be further diluted. Plus, I have heard that pre-soaked roots are better at absorbing fertilizer.

2. Here's how I fertilize (most) of my orchids. I think this will work well for the three types you mentioned. Mix the fertilizer at 1/4 strength and use it for 3 out of 4 waterings. It's called feeding weakly weekly. Use the diluted fertilizer just as you would water...pour it in the pot, using enough that the water starts to pour out the bottom of the pot. Let it drain completely, then sit in a saucer. I wouldn't allow it to soak in, but so long as you don't leave the fertilizer (or water) sitting in the saucer for days on end, it probably won't be a problem. Anyway, like I said, feed in this manner for 3 weeks/waterings, then on the fourth occasion, use only water, no food to help flush out any excess fertilizer that may have accumulated over the last three weeks.

3. For the plants you have, and most orchids in general, getting the food to the roots is most important, so definitely make sure you are fertilizing the roots. Plants can and do absorb nutrients directly through their leaves, but it is not usually a very effective means of fertilizing them. However, most orchids are prone to rot and infections resulting from water standing on their leaves for prolonged periods. So, when you consider the benefits versus the potential risks of spraying the leaves with fertilizer, I'd say general consensus is to avoid the practice. Most likely it won't kill your plants, but it's just not worth the risk.

(taking a deep breath, sorry for the long post, I tend to be wordy)

So, for your plants specifically...

The phal: Feed the phal year round, very weakly as they are definitely not big feeders and are especially sensitive to salts in the mix. Avoid getting water or fertilizer in the leaf crevices (and crown), and if you do, tip the plant over and let it all drip off. Phals are prone to crown rot.

The vanda: Will most likely take a short winter break in growth, even in Florida, especially if you aren't growing it in a greenhouse or under lights. So, if you notice that it's not in active growth, don't fertilize it, because it won't be feeding at that time anyway. With the vanda, you'll probably want to mix up the fertilizer in a bowl or small bucket, dip the plant down in to the liquid, let it set in there for atleast 10-15 minutes, pull it out and allow it to drip dry. You could also just hold it over a bucket and pour fertilizer over the roots, but vandas are a little tricky due to their propensity to develop aerial roots all along the stem, not just at the base.

The dend: I don't know anything about your dendrobium, but again, apply fertilizer to the roots, don't worry about applying it to the leaves. If there are no new growths forming/maturing, then there's no need to feed. Basically limit your fertilizing so that you're only feeding when the plant is actively growing.

    Bookmark   October 3, 2010 at 2:07PM
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Oh, one more thing with the phal, if you just repotted it, wait a month or so (or at least a few weeks) to fertilize it.

It was recently repotted and only had a few roots. It is stressed and the remaining roots don't need to be stressed further. It basically won't be in optimal feeding condition again until new roots have had time to form and make their way down into the new mix. So, feeding will mostly be a waste, and you'll just be adding salts to the potting medium with few or no roots to absorb it, they'll build up quicker.

    Bookmark   October 3, 2010 at 2:13PM
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Thanks Richardol and DigitalPhrag!

Both of your messages were extremely helpful and all the details give me some insight that will be helpful down the road. I plan to follow your instructions when feeding my orchids.

Thank you DigitalPhrag for your follow up message, because whether or not to feed the Phal was a big question in my head. I was not sure if it would need feeding to be able to grow new roots, but did not want to stress it out.

    Bookmark   October 4, 2010 at 8:51AM
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highjack(z6 KY)

You can always foliar feed an orchid, paying particular attention to the underside of the leaves so the stomata can absorb the nutrients.

Foliar feeding will eliminate salt build up in the media.


    Bookmark   October 4, 2010 at 10:00AM
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orchid126(z6, NJ)

You say you just repotted the phal into bark mix and "it seems water just runs right out from the potting mix on this one so I am not sure how effective pouring fertilizer over this." Did you soak the bark for several hours before using it? Bark needs to be conditioned before using it otherwise it won't absorb enough water. If you didn't, soak the whole pot for a couple of hours.

Also, you say your phal is on the dresser in your bedroom. How far away from a light source is the plant? Phals, while low light plants, do need light in order to survive.

I'm not familiar enough with your den to know whether or not it needs a winter rest. You will have to do some research on it, because if it needs a winter rest then fertilizing it at the wrong time will do more harm than good.

    Bookmark   October 4, 2010 at 3:33PM
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You're welcome Laura.

I meant to throw the phal comment into my first post, but it slipped my mind.

I thought it might be important to mention because I think a lot of people take the fertilizer is food metaphor a bit too literally and just assume that if food is good for a sick person, then fertilizer must be good for a sick plant.

But in fact, unless the plant is healthy and actively growing and has a good set of roots, fertilizing (at the root level) is useless and may even cause problems since salt will build up more quickly when there aren't any healthy roots to soak any of it up.

And yes, you can foliar feed the phal. Personally I wouldn't bother, especially with a sick phal since spraying any kind of moisture on the leaves is risky business. If too much moisture remains in the crown of the plant or leaf axils for too long, you'll end up with a rotting plant.

But, if your conditions are bright, warm, and breezy, and you make sure to spray the foliage early in the day, that should minimize the risk of rot.

    Bookmark   October 4, 2010 at 6:44PM
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penfold2(4b, MN)

Any new tissue growth requires nutrients, so repotted/sick plants need fertilizer just like healthy plants. They may not be able to absorb nutrients as quickly as a healthy plant, but that does not mean you should deprive them. If you are watering correctly (until significant water runs out the drainage holes), any unused nutrients will be flushed out at each watering, so nutrient accumulation is not a problem. I always fertilize repotted/sick plants, and have had great results.

And I agree with foliar feeding being a waste of time. It is very inefficient, and the moisture can be harmful. I always try to avoid getting water on foliage, especially late in the day when it may not have a chance to evaporate before night.

    Bookmark   October 4, 2010 at 10:04PM
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olyagrove(z9 Tampa, FL)

Hi Laura

Off topic...does your Dendrobium moschatum have any keikis - or perhaps you are interested in trading a division of it? I am Tampa as well. Have nice keikis of phal pulchra.

By the way, Phals grow really well in sphagnum moss in Florida climate (in clay pots)

    Bookmark   October 5, 2010 at 12:28PM
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Thanks for your help everyone! I really appreciate all you contributed.

@ orchid126:
I have repotted the Phal this week with potting mix that had been pre-soaked. I wonder why they don't include that in the instructions on the bag. Good news though, when I repotted the Phal a second time into soaked potting mix, I saw the roots are already doing better. :) And it is near a sunny window on my dresser (two other happy houseplants in the room).

@ olyagrove:
The Dendrobium makes new canes from inside the pot, so far no little guys that would be easy to remove.

    Bookmark   October 6, 2010 at 3:22PM
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olyagrove(z9 Tampa, FL)

The Dendrobium makes new canes from inside the pot, so far no little guys that would be easy to remove.
No problems, if you ever repot and need to divide, and interested in a local trade, let me know! I love huge tall Dendrobiums and always on a look out for more to add to the "collection" :)

Mama plant, Phal. pulchra:
From Orchids August 2009 From Orchids August 2009

As for fertilizing, I use Dynamite (slow released, sold at Lowes/Home Depot) - can put that in the pots twice a year. And liquid fertilizer when I have time - every two to three weeks - with a hose sprayer attachment. I do water lightly first and then soak up the orchid house with overly diluted liquid fertilizer. indiscriminately of genera...

Good luck

    Bookmark   October 7, 2010 at 8:12AM
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