Death By Drowning

clairecathyNovember 24, 2010

I've been reading about propagation methods and am -- as I often am in this garden journey -- confused. How is it that a cutting can be placed in water and happily grow long healthy roots, but a plant sitting in a PWT will have its roots rot and die?

Claire, who has forgotten any science she may have learned as a child.

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calistoga_al

Claire how long do you keep your plants in water without adding air by changing the water? Most plants in soil without air will not die in a few days. Al

    Bookmark   November 24, 2010 at 11:43AM
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clairecathy

Al,

I'm not speaking here from experience -- just reading.

If it's a matter of air, I can see that the water for cuttings is exposed to air in a way that the PWT isn't -- but why would *changing* the water be critical?

Is there some kind of "build-up" of waste in the water? If not, how is air content of the water changed by changing the water?

Claire

    Bookmark   November 24, 2010 at 12:06PM
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tapla (mid-MI z5b-6a)

The roots that form on cuttings rooted in water are quite different from those produced in a soil-like or highly aerated medium (perlite - screened Turface - the gritty mix ....). Physiologically, you will find these roots to be much more brittle than normal roots due to a much higher percentage of aerenchyma (a tissue with a greater percentage of intercellular air spaces than normal parenchyma).

Aerenchyma tissue is filled with airy compartments. It usually forms as a result of highly selective cell death and dissolution in the root cortex in response to hypoxic conditions in the rhizosphere (root zone). There are 2 types of aerenchymous tissue. One type is formed by cell differentiation and subsequent collapse, and the other type is formed by cell separation without collapse ( as in water-rooted plants). In both cases, the long continuous air spaces allow diffusion of oxygen (and probably ethylene) from shoots to roots that would normally be unavailable to plants with roots growing in hypoxic media. In fresh cuttings placed in water, aerenchymous tissue forms due to the same hypoxic conditions w/o cell death & dissolution.
Note too, that under hypoxic (airless - low O2 levels) conditions, ethylene is necessary for aerenchyma to form. This parallels the fact that low oxygen concentrations, as found in water rooting, generally stimulate trees (I'm a tree guy) and other plants to produce ethylene. For a long while it was believed that high levels of ethylene stimulate adventitious root formation, but lots of recent research proves the reverse to be true. Under hypoxic conditions, like submergence in water, ethylene actually slows down adventitious root formation and elongation.

If you wish to eventually plant a rooted cutting in soil, it is probably best not to root them in water intitially because of the frequent difficulty in transplanting them to soil. The brittle "water-formedâ aerenchymous roots often break during transplant & those that don't break are very poor at water absorption and often die. The effect is equivalent to beginning the cutting process over again with a cutting in which vitality has likely been reduced.
If you do a side by side comparison of cuttings rooted in water & cuttings rooted in soil, the cuttings in soil will always (for an extremely high percentage of plants) have a leg up in development on those moved from water to a soil medium for the reasons outlined above.

The short answer is that plants rooted in an airy medium get the O2 necessary for normal root function/metabolism from the soil. Plants rooted in water form a different type of tissue, by one of two biological processes, that allows the O2 required for root function/metabolism to be moved from shoots to roots. Since these tissues develop to allow the plant to cope with one condition or the other, not both, they are very poor at making transitions.

Al

    Bookmark   November 24, 2010 at 1:43PM
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greenman28 NorCal 7b/8a

Excellent! Thanks for the refresher, Al!
Gotta copy this post.

Josh

    Bookmark   November 24, 2010 at 1:59PM
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clairecathy

Al,

Thanks for this satisfyingly complete answer. I'm also happy to have some understanding of what method of propagation to avoid in the future :)

Since I know of no icon for bowing, I will convey my feelings of respect here with a sign that has the kinetic feeling of that movement. @

Claire

    Bookmark   November 24, 2010 at 2:14PM
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tapla (mid-MI z5b-6a)

Lol (an embarrassed laugh) - no bowing necessary; but an acknowledgement of the attempt to help always feels good. :-) Thanks, guys.

Al

    Bookmark   November 24, 2010 at 3:35PM
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meyermike_1micha(5)

How about a beer then Al?

Thank you so much for this refresher too..
I am like Josh.
I love to save this info..

Mike:-0)

    Bookmark   November 24, 2010 at 4:17PM
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jojosplants(9/ Tucson, Az.)

Saving here too. :) clip or print. :)

Happy Thanksgiving Friends!
I hope you all have a wonderful day tomorrow.

JoJo

    Bookmark   November 24, 2010 at 4:54PM
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jodik_gw

We are not worthy! (As Wayne and Garth would say.)

In my own experience, everything Al says is true. One of the only plants I've had luck moving from water to soil is the lowly Pothos... and you can throw pieces of that right into the fish tank, and it will survive and grow... under water! Of course, air stones continually move plenty of oxygen through the water, so... there ya go.

Another plant that transitions rather well is the spider plant. But the roots of both the Pothos and the spider plant, when rooted in water, are a lot more brittle than roots grown in soil.

Most everything else I've stuck in jars of water to root has died. The better method... for myself, at least... is to place cuttings in soil, and apply bottom heat using a small heating pad. The warmth helps promote root growth. I also keep the potted cuttings out of direct sun, so they can place their energy into root production instead of photosynthesizing. I think that's correct, anyway!

Thank you for the science lesson, Al... the technical terms are sometimes a bit above me, but the general ideas always stick. :-)

    Bookmark   November 27, 2010 at 5:41PM
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clairecathy

Jodik,

" apply bottom heat using a small heating pad."

This is very interesting. Do you use an ordinary pad with Low heat? With a plastic pot? Directly under or with some intermediary barrier? Day and night? Just for a month or so? I would have thought that was too much heat! But my apt tends to be cool to cold and maybe this would help.

Claire

    Bookmark   November 27, 2010 at 6:27PM
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tapla (mid-MI z5b-6a)

There are mats of varying sizes designed specifically for use in propagating, which is prolly why they are referred to as propagation mats. (Do a search for "seedling heat mat") These mats tend to be designed to raise soil temperatures about 10* above ambient temperatures. There are also thermostats available to be used in conjunction with these mats so the soil temperature can be controlled to within +/- 2*. As a generality, with most plants, best rooting success is achieved when rooting media temperatures are between 65-75* and ambient air temperatures about 10* lower. Bottom heat is usually halted as soon as rooting has occurred.

Al

    Bookmark   November 27, 2010 at 8:57PM
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clairecathy

Al,

Ahh. As always, everything I needed to know. :)

Thanks so much.

Claire

    Bookmark   November 27, 2010 at 9:40PM
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suddensam(10 Boynton Beach)

Al, Thank you again. I get on people about the medium they use and drowning there plants and I get it threw at me about starting cuttings in water. Frankly I didnt know how to answer it. Im reading over and over your post so I know what im talking about, so I can answer them.
Plant em if you got em.
Sam

    Bookmark   November 27, 2010 at 11:44PM
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kate724(6)

This might be of interest.

Here is a link that might be useful: Hydroponics

    Bookmark   November 28, 2010 at 12:28AM
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greenman28 NorCal 7b/8a

Kate, there's actually a Hydroponics Forum at this site.
What we're discussing here is the propagation of plants in still, non-aerated water.

There's nothing wrong with hydroponic growing, but if one is planning on switching a cutting to soil,
then it's really most efficient to just root in a soil-mix from the start.

Josh

    Bookmark   November 28, 2010 at 12:37AM
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calistoga_al

I have rooted many plants in aerated water and successfully transplanted into soil in pots. The reason I don't do it is because I can't think of a good reason to add an extra step to my propagation. It was fun to work out a good system of rooting in water, but that done, I lost interest. Al

    Bookmark   November 28, 2010 at 7:58AM
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jodik_gw

The heating pads I use are sold at most garden centers... usually in spring with seed starting displays... and come with a 72 cell flat, an outer tray, and a tall, clear plastic greenhouse-like cover. The entire ensemble costs about $20, or so. I've got two.

When plugged in, they keep a low to medium level of heat under the flat, which helps to promote growth... of either seeds, or I use it with cuttings.

You can use them with the flat, or without. I like to put a buffer between any pots and the pad, just to help keep everything at a heat level I like. I use a coffee can lid or a lid from tupperware, or whatever I have handy as a buffer.

There are also larger table sized heater units for greenhouses... but they're terribly expensive. An alternative is a heating unit made for the farm industry, for farrowing pigs. It comes with a thermostat and a removable cord. They're quite large. I'm not sure of cost.

I don't know for sure, but I would guess you could get heating units or pads in different sizes through the greenhouse industry. You could try Googling, and I'm sure the results would be many and varied.

Bottom heat does promote root growth, and is likened to the ground heating up in the spring from the sun and rising seasonal temperatures. The growing/greenhouse industry uses bottom heat quite a bit in rooting items and in seed starting.

    Bookmark   November 30, 2010 at 10:52AM
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clairecathy

Thanks, Jodik. After Al posted, I went online and found some heating units to choose from, so your mention of this, and the follow-up, are much appreciated.

Claire

    Bookmark   November 30, 2010 at 10:59AM
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jodik_gw

No problem, Claire. I'm glad you found what you were looking for. :-)

I've found my little heating pads to be quite indispensable. I use them often for rooting things and for seed starting. No serious gardener should be without! ;-)

    Bookmark   December 3, 2010 at 5:06PM
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greenman28 NorCal 7b/8a

I use the Poor Man's heating mat ;)
....which is to say, black plastic trays and black/dark colored containers.
Of course, I live in a comparatively mild climate!

Josh

    Bookmark   December 4, 2010 at 11:26AM
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meyermike_1micha(5)

I have one!

Great advice Jodi!!

I like Josh's idea...My little one cost me 45 bucks!

I tell you though, it is worth the investement..

Mike

    Bookmark   December 4, 2010 at 11:54AM
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tapla (mid-MI z5b-6a)

I have a couple of buttonwood bonsai that absolutely require warm soil, so they're on a mat. The rest of the time I use them for propagation to keep soil temperatures at 70* *, THAT, only when air temperatures are cooler than that.

For most propagation, soil temperatures are best around 70*, with air temperatures being about 10* cooler.

Al

    Bookmark   December 4, 2010 at 12:07PM
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jojosplants(9/ Tucson, Az.)

At the moment, I am using the same method as Josh. ;)
One of these day's i'll get around to getting a matt. :)

Hello everyone!

JoJo

    Bookmark   December 4, 2010 at 8:43PM
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