The 'water twice' approach to watering

[richgarrison]

I've heard the 'water twice' approach to watering a multitude of times from many people, some of which i tend to trust implicitly. In all cases the speaker discussed authoritatively the value of watering twice in getting a thorough watering of the plant. and for me that aspect of the discussion has always been proven by experience.

The part that appears to be less 'authoritative' is the procedure of which watering includes the fertilizer (or maybe both). I've tended to buy into the 'gut' feeling that fertilizing first made sense since in nature when it rains that first solution hitting the roots will have the most nutrients. (heard this first from @Ray )...

In some random reading i came across a reprint of an article published in Orchid Digest (Orchid Digest, Jan., Feb., Mar. 2015) written by Carol Siegel entitled 'The Secret Life of Orchid Roots' where she references research by Zotz and Winkler where this topic was studied... Since i haven't actually tracked the reference down and read it, i won't say what it concludes, but Carols article states "Gerhard Zota (mis-spelled?) and Uwe Winkler did a series of experiments showing that velamen allows the orchid to capture and retain the first solutions arriving in a rainstorm, which have the most nutrients."

so.... i don't know about you, but i can certainly sleep better at night now that this debate appears resolved..



Zotz, Gerhard and Uwe Winkler. “Aerial Roots of Epiphytic Orchid: The Velamen Radicum and Its Role in Water and Nutrient Uptake", Oecologia, 141 2013:733-741

 

[Greenpaph]

Interesting! Thanks for sharing!

 

[Ozpaph]

i fertilize first, then later water. Seems logical when you look at exposed vanda and phallie roots - after wetting them, they are 'saturated'.

 

[Ray]

Zotz and Winkler compared the velamen of several different genera of orchids - some thick, some thin - and concluded the existence of a cation trapping ability.

To me, it makes sense, in light of the natural dynamics of living in a forest, where rains wash the nutrients out of the canopy almost instantaneously, followed by a pure water deluge thereafter.

Alan Koch (Gold Country Orchids) told me it wasn’t true, but did not back the statement up, so I’m still going with it.

 

[richgarrison]

Zotz and Winkler compared the velamen of several different genera of….

Alan Koch (Gold Country Orchids) told me it wasn’t true, but did not back the statement up, so I’m still going with it.

He was one of the ones I had in that ‘trust implicitly’ category….

I’m sticking with the fert first approach. Hasn’t caused any Ill effects yet.

 

[awesomei]

For many years now. I have always flushed with fresh clean rainwater first, to remove all old solids. Then, I water a second time with my fertilizer solutions. This always seems to work well for me!
George

 

[cnycharles]

If your plants are over dry, and you are going to feed with something really strong, it may be better to hydrate to a better level and then at some point give a feed. Also if you are a heavy feeder and you let your plants get really dry (like cattleyas possibly) then you can get built up dried up salts on the surface, and it may help to loosen them up with water first and flush, then later feed. But if you do cyclical watering (feed one time and water a few days later) and don’t let things get too dry in between then that could accomplish feeding and flushing. In nature probably things don’t get as dry as in culture or have heavy fertilizer sitting on it. If you feed lightly and never really let things get dry, then the jungle example could be accurate

So the answer is ‘it depends’

 

[Ray]

So the answer is ‘it depends’

And what, in orchid growing, doesn't?

 

[Sky7Bear]

Thanks, Ray, for your input. I have always watered first and then fertilized, but that doesn't mean it's right. However, I think you have noted elsewhere that the game is quite different for those of us growing in semi-hydro, which means the roots are always wet and hydrated. This would be true for several other genera which don't like to dry out at all. I'd put Phrags, Miltoniopsis, Masdevallia and Disa in that category, even when grown in organic media. Mounted, of course, always get dry velamen, but I'd say for me almost nothing else does. So I go with a fairly weak solution of fertilizer as the last stage of watering after 3 rounds of pure RO water to flush out any minerals that remain in the container.

Indeed, I don't fertilize at all from Halloween until about now, just before Imbolc n the Celtic calendar (halfway between the winter solstice in the northern hemisphere and the spring equinox, also known as Candlemas, St. Bridgid's Day or Groundhog Day). This gives the medium a chance to be thoroughly flushed when there is little growth, but I can already see new growth right on schedule, about MLK Day. I grow almost nothing in pots that dries out in between, though I have a friend who does very well with Phals in large Orchiata that he makes sure is dry before re-watering (would probably work well with Catts as well). He thinks it's about water, I think it's more about air, but it doesn't matter as his roots are adapted to that growing condition.

 

[Ray]

Personally, I think the only things “wrong” with watering first, then feeding, are doubling the amount of time needed for the task, and potentially wasting fertilizer more than we already do, considering the large “pour through” of orchid media - neither of which is a big deal.

@Sky7Bear - while I think that no food for months may lead to better leaching of mineral residues from the medium, I suspect it’s not as thorough as assumed.

Minerals are pulled into the interior of media as the solvent evaporates, outside-in, concentrating as it does so. It takes a relatively long time for water to penetrate into the subsurface cells, redissolve the solids, then carry them back to the surface to be carried away, so the extraction by the brief flow of plain water isn’t all that efficient.

I had someone tell me they tested the EC of the drainage water an “knew” they had completely cleaned out the mineral buildup because the EC was essentially unchanged, but when they took that medium and let it sit in RO water overnight, the EC was a lot higher than they realized.

 

[Sky7Bear]

Well, Ray, I water first so as to leach out the salts, but then we don't really know that it works! LOL. If I'd thought of it a couple of weeks ago before starting fertilizer again, I might have tried some experiments. Perhaps I still have some leca outside (that's also been rained on!) that I can soak and measure with just to see how much it invades the interior of the leca "ball." I do reuse leca, and so I would expect to leach it in any case. Let's see what still comes out. As far as only a weekly basis, perhaps a good point. I do like to make sure that the plants are thoroughly watered and overwatering in S/H is one way to make sure it happens, and perhaps more air gets into the pot. Always more questions than answers. And yes, it does take more time, probably for me about 15 minutes. Maybe I should return to one water only watering with one only fertilizer only. Of course, the reservoir is never empty for me, and so who knows how much fertilizer even gets into it. AND, the plants seem happy, so perhaps leave well enough alone, especially now that days are getting longer. So, I will measure what I have with plants that have died. LOL.

 

[Russ1992]

What would be great is if we had empirical, quantitative evidence to test these various methods to see what actually creates the best looking plants. For a true scientific case study there needs to be a sampling of 120 individuals. That's a lot of time and money for any hobbyist but it's more feasible if you're retired, have the space, the means, and the time; I don't fit the majority of the criteria. I guess one can get large samples by working with flasks.

 

[Ray]

When I lived in PA, I was near the Fetzer Greenhouses in Hartsville. Once upon a time, that had been a big source of cattleya hybrids, complete with flasking lab and incubation rooms. Dad died, and his son converted the place into more of a seasonal bedding plant/poinsettia nursery. He did, however, have a relationship with Hausermann, so had a few greenhouses with flats of phals and oncids that should have been potted up years earlier, but still sold for $1/plant. They were the supply of plants I used in my various comparative experiments - one concerning the use of synthetic hormones (including my own concoction), and another concerning the impact of daily watering. Each experiment dealt with 300 plants, broken into sets “matched” by observed size and weighed as a group to provide an objective parameter.

All gone now - property values were worth more that the business could possibly generate.

 

[NYEric]

I got the "water twice" advice from Terry Root (OZ).

 

[Ray]

Before I even had an orchid, I was helping feed them at what is now the Atlanta Botanical Garden. We used to water heavily first, then repeat the process with VERY concentrated fertilizer - on the order of 500 ppm N. A huge waste of a pollutant, and totally unlike what the plants are exposed to in nature.

 

[geoffsharris]

Food for thought. The reason it is so hard to make a general recommendation is that orchids occupy a lot of different niches and get exposed to a lot of different moisture and nutrient availability regimens. Think of a Tolumnia with its roots mostly in the air and infrequent heavy rain vs. a Phrag besseae in nearly a constant stream or seepage of fairly pure water. Moisture and nutrient exposures are very different. Further, many orchids have roots associated with mosses, detritus, lichens and associated fungal hyphal networks that dictate moisture and nutrient availability that is linked to, but not controlled strictly by rainfall timing and duration. The idea that all orchids should get nutrients in a fast bolus either early or late in a quick blast of water just doesn't represent what happens in nature, but it is the way we generally water them as growers.

So what is a grower to do? If you think about the velamen on epiphytic orchids in particular, they have evolved to fairly quickly blot up water until they are saturated and then don't really take up further water until it is mobilized up the root to the plant which takes hours. There are three phases to absorption. First wetting the velamen, second - significant uptake of moisture and third - saturation. You don't get any use (nor harm at least to the plants) by providing nutrients in the wetting phase or at the saturation phase. If you want to maximize your mileage on providing the least amount of fertilizer that is effective for the plant without wastage, do the following. Give a light spray of the roots with fine mist to get the velamen to start to absorb water. A fine mist works a lot better than a coarse watering. We have all had the experience that at first the roots are a bit hydrophobic and continuing to water them does little except wet the greenhouse floor. Once they start to absorb water, do a second pass with the fertilizer solution. Now the plant will absorb the majority of the water until it is saturated along with the supplied nutrients. A final light rinse, particularly of the foliage with no fertilizer is often a good idea as you are reducing the availability of nutrients to algae, bacteria and fungi on the foliage, especially in the bracts of plants.

The reason for the recommended two waterings by commercial growers is partially based on achieving maximum hydration of the plants and to reduce nitrogen pollution/ fertilizer costs. A single quick blast of water for mounted plants or ones in very coarse media mostly just gets you through the wetting phase and not to saturation so the plants aren't as hydrated as you would like them to be from the watering. As a commercial grower the cost aspect tends to be bigger considerations than for most hobbyists. For plants that are generally fairly continuously moist, two waterings is mostly a waste of time and is much more important for plants with a significant wet dry cycle - think Vanda or Cattleya.

Flushing the plants is kind of the same thing. The first pass of water will start to solubilize mineral build up and a second pass will flush it out. You could just as easily just keep watering the plant with 10 times as much water to achieve the same thing (or dunk in a bucket for an hour), but this wastes time and water. Two moderately fast passes is much more effective than a single pass.

 

[NYEric]

 

[Brabantia]

In my experience, the best way to water with or without fertilizer is to do it in two steps on a dry substrate. This is how I proceed. First water until the water runs out slightly from the bottom of the pot and then water again after 10 to 15 minutes. I am always surprised how much water I can still add. The problem is that in general the substrate that contains bark (or CHC and also sphagnum) are a little hydrophobic (when they are dry) . Perhaps the addition of a wetting agent in the water or fertilizer solution could facilitate the wetting. But ... which wetting agent is compatible with our orchids ? The ultimate method is to dip the pot directly into the solution but what about the transmission of diseases or undesirable from pot to pot and the amount of water needed.

 

[cnycharles]

There is a combo wetting agent/disinfectant that is often used with plants. It’s called Uptake. It’s often applied to clean benches and hard surfaces to disinfect, and water lines. Also sprayed on plants to help wash off and dull/inhibit present diseases on the surface. I don’t know if it will make bark hydrophilic (not resist water). There are labeled rates for disinfecting surfaces and plant matter, and rates for soil wetting. Experimentation with the listed rates on different orchids would be needed before safely using. Many perennial seedlings accept application though some show burns, usually if the plant is very small/young or it’s applied more often than every two weeks (the suggested label recommendation). You would need to research the product and make your own determinations based on the instructions. It doesn’t help inhibit every surface disease, the label would show what it was effective against.

Note: if using with concentrated fertilizer solution it may cause precipitation. Read the label to determine if it can be used with fully hydrated fertilizer solutions (not concentrated, ready to apply). It is not suggested to mix with concentrated solution as any iron will separate, and who knows what else. Again, the label will show what it can be tank mixed with

 

[NYEric]

Thanks Charles.