Gardening Ideas forum: Sunday afternoon experiment: watering in multiple passes

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Name: Baja
Baja California (Zone 11b)
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Jul 30, 2017 4:35 PM CST
Here's a little experiment I did to test my own advice to water succulents in more than one pass. I was kind of surprised by the results so I thought I would share. It's very much something you can try with your own plants. There are some useful conclusions from this, I think.

The idea is that bone-dry soil does not efficiently absorb water. Only after it has become moist (which takes some time) does it absorb efficiently. In order to test this I chose a cactus in soil I knew to be completely dry at the start.

I poured a measured amount of water (very carefully) onto the soil all around the plant until it started coming out the bottom, having passed through all the way. Then I let the plant sit for 15 minutes to make sure all the water had exited the container. At that point I collected the water in the saucer (very carefully) and measured how much was there using the same measuring cup. By subtracting this amount from the total input, you can arrive at a volume of water absorbed by the soil during each pass.

Here is the setup and the results.

The cactus is a stout Parodia from my balcony, where it grows in pretty much day-long full sun. It takes a week or less to dry out completely. When I set it in the saucer, I put in a couple of wood spacers to make sure the pot never ever sits in standing water.

Thumb of 2017-07-30/Baja_Costero/ae18d2 Thumb of 2017-07-30/Baja_Costero/b5317e

This is what I recorded after the first pass, when I poured on 500ml and recovered 170ml.

Thumb of 2017-07-30/Baja_Costero/6e1151

And this is how much water was absorbed during each pass, separated by 10-15 minutes.

pass 1 - 330ml
pass 2 - 210ml
pass 3 - 100ml
pass 4 - 60ml
total after 4 passes - 700ml

Which tells you that if you stop watering after the first pass, the soil may achieve less than 50% saturation, even if you are watering until water comes out the hole in the bottom. That's why I recommend watering in more than one pass.

Try this yourself (no special tools required) if my result surprises you. Smiling I recommend a largish pot to make the measuring easier.
[Last edited by Baja_Costero - Jul 30, 2017 4:52 PM (+)]
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Name: Kristi
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Jul 31, 2017 7:46 PM CST
Thank you for sharing that information. I find that most interesting and would not have realized that.

I shall have to change the way I water the succulents collection. Thumbs up
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Name: Karen
NM (Zone 7b)
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Jul 31, 2017 7:49 PM CST
I also found it very interesting, and will have to change the way I'm watering my cacti and succulents. Thanks, Baha!
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Name: Cheryl
Texas (Zone 9a)
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Jul 31, 2017 7:58 PM CST
I do this watering method for all my non cactus plants when I hand water! I water quickly til it runs out the bottom tending to all the pots walking in a circle pattern. Then return in the opposite direction giving everyone a second drink. I can hear them say, "Ahhh!" on the second pass, and lick their lips, as if plants have lips. They truly enjoy a good watering. And with this method I know it's not wasted but soaked in.
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Name: Baja
Baja California (Zone 11b)
Cactus and Succulents Seed Starter Foliage Fan Xeriscape Container Gardener Hummingbirder
Native Plants and Wildflowers Garden Photography Region: Mexico Plant Identifier Forum moderator Plant Database Moderator
Jul 31, 2017 8:45 PM CST
Yes, that's a good point about the wastage too. I actually water less than any container can absorb (my handy squirt bottle has a pretty even flow rate) during any pass until the final one. Which is to say I go slow and then stop watering when I see flow through, or maybe flush a bit more for good luck. Pretty much the minimum wastage.

To the extent you can hear air being slurped out of certain containers, I can often hear a little snap crackle and pop in there on the second and third rounds of watering, when they're absorbing the water the fastest. There's a certain sound when the soil is actively slurping, and that provides a great independent confirmation of what's going on underground. Thumbs up The auditory experience is much more intense when it's hot and dry.
[Last edited by Baja_Costero - Jul 31, 2017 8:53 PM (+)]
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