My Phal potting mix, watering regime & method - Orchid Board

OzPhal · #1 08-02-2012, 07:47 AM

Hi folks,

Yet another post about my potting mix, watering regime and watering methods - my apologies - a picture paints a thousand words! So attached are some pictures of my seedlings freshly potted in 50mm clear pots and my 4 part bark, 1 part perlite, 1 part charcoal media in my growth chamber (constant 28oC and now 80% RH with a 14hr on 8hr off light cycle). These are all Phalaenopsis species.

Seedlings in the growth chamber

All of the seedlings were watered at the same time so they're displaying different drying rates:

Damp potting media - not ready for re-watering

Dried potting media - would you re-water this now or give it another day?

View through side of pot in the 'damp potting media'

So what do you experienced growers make of the above photos? also, how would you water those seedlings? I've heard many refer to the "firehose" watering method but wonder if i should wait to use that method until the seedlings are better developed. If you do use the 'Fire hose method" how do you fertilise? At the moment I was thinking of just holding my hand over the bottom and filling the pots completely - or sitting them on something so that the water will remain in the pot for a minute or so to soak in to the bark. Thoughts? Suggestions? Also, I've noticed on the tip of some roots that the growing tip is swollen and a nice green but just behind that it kind of restricts - the root is a nice colour, but what is that situation? too little moisture to the roots? adjusting to having been repotted? or is it normal? I watered the seedlings on monday, it's now thursday and i'm going to water tomorrow (Friday) - those photos were taken on wednesday so three days after watering... as i'm sure you can tell watering, and watering correctly, is one area that's causing me some anxiety. Also, I know this is an ironic question given the goal of phalaenopsis potting mix, but does it matter if there's air pockets in the mix? Does that potting mix look ok for those sized seedlings? I also regularly mist the leaves and top of the potting mix

#2 08-02-2012, 07:56 AM

Those are great looking seedlings, I think you are doing great job!
I just deflasked two flasks with phal hybrids for the first time and have exactly same worries

I can't give any advice on watering bark because my phals and seedlings grow in straight moss, but I use a one day rule a lot(If you are not completely sure that plant is ready for watering - wait one more day).
Also, since your chamber has high humidity I would be very careful about misting the leaves.
Good luck with your seedlings.

zxyqu · #3 08-02-2012, 09:27 AM

A couple things I'd point out. First being are those pots roughly the size of the root ball for each phal. Generally phals like to be tightly potted (though I'll admit some of this is for overwatering concerns). Just a quick thought there
Secondly, I dont grow in this media, nor in your conditions, so it will be tough to accurately comment. Orchideya's comment of the one day rule is solid, and will prevent some of the overwatering. You can't use the appearance of the top of the media to indicate when you need to water. Trust me here, as if you do, you'll kill a lot of phals. So try a skewer of sorts (chopstick, similar), or learn the weight of the pot when it needs to be watered. You'll pretty quickly be able to "feel" when it needs to be watered, just by picking them up. Also, with your increased humidity, don't be surprised if you only water weekly, or even longer than that (and no that is not a cause for concern).
As to how to water, I'd still recommend the firehose method. Pick up a pot, flush it with water (being careful to avoid the crown in general), and replace it. After you're done do a quick q-tip wipe off of any wet crown to limit crown rot potential. This will flush excess salt/mineral buildup out of the pot, something bottom watering can't do.
Finally, I wouldn't mist your leaves either. You've got high heat and humidity, and excess water on the leaf surface could cause some issues. At 80%, I doubt they need much more water.

OzPhal · #4 08-02-2012, 09:43 AM

Thanks guys for the feedback - I really appreciate your input. In regard the pot size - there's plenty of room for the root balls to grow - those 50mm pots are the smallest I could get. I understand what you mean by the firehose method now - I thought you literally used a hose but I guess you could use a watering can too. Do you close off the bottom at all or just let it flow through? I'll use the skewer in conjunction with learning the weight... I don't want to kill these babies!

zxyqu · #5 08-02-2012, 09:46 AM

Just let it flow right through. Lots of people do it lots of ways. You can use plain water first, then repeat with weak fertilizer. Or you can use fertilizer only just one time. It's your choice. Remember to very weakly fertilize tho. 1/8 to 1/4 of the recommended rate.

OzPhal · #6 08-02-2012, 06:30 PM

Quote:

Originally Posted by zxyqu

Just let it flow right through. Lots of people do it lots of ways. You can use plain water first, then repeat with weak fertilizer. Or you can use fertilizer only just one time. It's your choice. Remember to very weakly fertilize tho. 1/8 to 1/4 of the recommended rate.

Thanks for that - much appreciated! I'll give it a shot with water first and then after that's soaked in use some fertiliser...

james mickelso · #7 08-02-2012, 11:51 PM

There is an old maxim....never fertilize a dry orchid. Water first, then water with a weak fertilizer solution. The reason you don't want to over pot an orchid is that the orchid roots can't absorb all the water in the mix, and fungus starts to grow and rot the roots. But if you have a good amount of air flowing over and around the roots, then you can pot them in larger pots because the roots and media dry out more quickly. The point is to make sure they dry out before the fungus can take hold. That is the reasoning behind not over potting orchids. And a lot of folks pot in spagnum moss which dries slowly. But with sufficient air flow the moss dries out in a reasonable amount of time. Wynn Dee pots in moss. She has fantastic results. I'm not a fan of moss at all. I don't have much luck with it. I live at the beach and it is always humid so moss doesn't dry well. Even with my huge fan.

RosieC · #8 08-03-2012, 09:11 AM

Although the old advice of watering first went with much more concentrated fertilizer.

Old thinking was fertilize once a month with concentrated fertilizer. In that case root burn on dry roots was common so watering first was best.

Modern thinking is to water weekly weakly. The less concentrated fertilize is a lot less likely to burn the roots. In fact with that its best to NOT water first as then the roots can't absorb enough fertilize (they are full and can't absorb much more).

I use weekly weakly and always include fertilizer in the watering water when the roots are dry. I use Ray's calculator for concentration rates to do this.

Ray · #9 08-03-2012, 09:35 AM

Rosie is right. Back when I was new at orchids (early 1970's), and helped with the orchid collection at what is now the Atlanta Botanical Gardens, the common practice was to feed monthly, using a VERY strong fertilizer solution - it would dye white blossoms blue! If you applied it without watering with plain water first, it would have surely poisoned the root systems.

By watering with plain water first, you saturate the medium, but more importantly, the velamen on the root system, so that it cannot take up very much more when you apply the fertilizer. With the strong fertilizer application, there will be some diffusion into the saturated medium and velamen anyway, but if you use more modern feeding techniques with much lower concentration, the amount of absorbed nutrients will be so small that the plant will get little to nothing.

Ray · #10 08-03-2012, 10:02 AM

James is correct about issues with overpotting in most media, but I think a few of the the causes-and-effects are actually a bit different.

☼ The drying of any potting medium relies far more on evaporation than it does on absorption by the plant, which is orders of magnitude smaller.

☼ Roots do not need to dry out between waterings.

☼ Except in extreme cases, fungi do not kill and destroy roots. The roots have to be severely weakened or dead for the fungi to start the decomposition process.

The reason overpotting can be an issue - with some media - is that it can lead to the suffocation of the roots.

When we water, most pours right through. Some is immediately absorbed by the medium and root system, and some is held by surface tension in between the particles of the medium (or between the medium and the pot wall, as shown in that last photo, above). It is that last category, the "bridging water" that is the issue.

Let's shift our thinking to the pot of medium for a moment. Most of the evaporation occurs from the top surface and the medium/pot interface. Therefore, the center "core" of the medium - right in the middle of the root mass - stays wet the longest.

The ability of surface tension to hold water is limited to small spaces, so if the potting medium is too fine to begin with, is decomposing and breaking down into fine particles, or becomes compressed, the amount of bridging water is significant, can cut off all air flow in the root zone, and can lead to root suffocation before it is absorbed or evaporates. If the medium is relatively coarse, or effectively absorbs and wicks away the moisture (as LECA does), there is no danger of root suffocation, nor a concern about overpotting.

I grow my phals in semi-hydroponics, using LECA medium and keeping them constantly moist, and I try to use pots that are equal in diameter to the leaf-span of the plants. They grow very well, and don't put out aerial roots. If I tried that with a bark-based medium with irregular-shaped particles that pack to tightly and don't wick well, I'd have a large supply of dead plants in fairly short order.