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water Irrigation interval - 24 or 48?
- Thread starter JohnT
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Mornin' JT. I had researched/typed a post late yesterday but hit the "Discard" button by mistake. Will reconstruct it this morning..
As noted by Solid7 , over-watering is usually confined to containers due to Perched Water Table In Containers (Which he has posted about here.). In contrast, in ground usually don't have that issue unless there is an issue below the garden, Perched water tables:
"A perched water table (or perched aquifer) is an aquifer that occurs above the regional water table, in the vadose zone. This occurs when there is an impermeable layer of rock or sediment (aquiclude) or relatively impermeable layer (aquitard) above the main water table/aquifer but below the land surface."
To address your dilemma, try both. As long as the plants don't wilt the way that saves money the best!
As noted by Solid7 , over-watering is usually confined to containers due to Perched Water Table In Containers (Which he has posted about here.). In contrast, in ground usually don't have that issue unless there is an issue below the garden, Perched water tables:
"A perched water table (or perched aquifer) is an aquifer that occurs above the regional water table, in the vadose zone. This occurs when there is an impermeable layer of rock or sediment (aquiclude) or relatively impermeable layer (aquitard) above the main water table/aquifer but below the land surface."
To address your dilemma, try both. As long as the plants don't wilt the way that saves money the best!
Thank you thank you all.
Damit I set it for 24 hours and it is not easy to set mine. You have to be there and I am laze and don't want to be up that early.
Maybe I can change the interval at any time of the day, versus the start time, which I MUST be there. I got this timer at a thrift but it has done me well over the years. The batt compartment even has a rubber ring / gasket and the battery connections are as new (seriously clean like factory) right now. Takes two 9 v and they last the season easy.
In regards to perched water table. I do fill the bottom of my containers with coarser material although I accept that is no guarantee. My dad taught me that we once got these epic tree containers from a landscaper and he had me pay money to buy bark mulch to put in the bottom, to facilitate drainage.
Damit I set it for 24 hours and it is not easy to set mine. You have to be there and I am laze and don't want to be up that early.
Maybe I can change the interval at any time of the day, versus the start time, which I MUST be there. I got this timer at a thrift but it has done me well over the years. The batt compartment even has a rubber ring / gasket and the battery connections are as new (seriously clean like factory) right now. Takes two 9 v and they last the season easy.
In regards to perched water table. I do fill the bottom of my containers with coarser material although I accept that is no guarantee. My dad taught me that we once got these epic tree containers from a landscaper and he had me pay money to buy bark mulch to put in the bottom, to facilitate drainage.
I guess one more thing to say is I once grew a habalokia in a 7 gal black pot, which was and still is the biggest success story I have had. Lots of luck was involved. Half a decade ago. The rootball was the entire container. I pulled the plant out, and the whole cylinder of grow medium came out, wouldn't separate. I can;t tell you if I irrigated daily but I suspect at some points I indeed did, if nothing else during the warmer weeks.
JohnT said:
No, that is not a good practice. Putting a different media in the container only pushes the perched water table up higher, and does the exact opposite of what you think you're doing with the coarser material.
Perched water tables work on a differential between the specific gravities of two materials. The PWT is an absolute, it is not relative to any shape, volume, etc. If you have a material that holds 3" of water in the bottom, at its saturation point, then you will have 3" of water in the bottom, whether your container is 18" deep, or 3.5" deep, whether it's conical, spherical, etc, etc, etc. So if your container was 18" deep, and you added 3" of coarse material to the bottom, you now have 12" of container space that is not affected by the PWT. Whereas if you had left just the original media, it would have been 15" of non-impacted container space.
The PWT works just like a sponge... You can pour water into a sponge, and it will absorb, up to a point. However, when it's saturated, the water will begin to drain under its own weight, with the sponge not longer being able to hold up the water. (remember that weight is defined as mass X gravity) Even so, you could still squeeze out a substantial amount of water, even after it begins to drain. That saturation point would be the sponge's PWT.
In short... don't add "stuff" to the bottom of containers, thinking that you're getting drainage. You're just cheating yourself out of container capacity.
My containers all have drainage holes around the perimeter on the bottom.solid7 said:
I still may not be understanding. I have not seen the effect described, and my containers are emptied each year.
I could be wrong but I think PWT is a fancy way of saying the growing medium is waterlogged. I don't know. The cure for that is soil structure. Or that's what my background has taught me.
JohnT said:
There is no cure for a PWT. It's a consideration OF structure. EVERY growable media has a PWT. The cure is, don't put anything in the bottom of your containers, that isn't what you're growing in. Or you're just creating the potential for more water retention in the bottom of the container, and/or lesser growing space in the actual media.
Summary:
Container full of well-built growing media = GOOD
Container full of well-built growing media with something else added at the bottom = BAD
solid7 said:
Got to disagree with you. 'Stuff' added to the bottom of containers isn't to effect the PWT for me. Its to keep the drain holes from getting clogged with compacted soil or 'chunks' of mix. A soft water absorbing piece of wood/compost/peat/bark that fit perfectly on top of the drain holes effectively blocking/sealing them with soft conforming surfaces, no good. IMO anything one can do to facilitate fast complete drainage in containers is a good thing...
I always put washed gravel/small rocks in the very bottom of all my 'solid' containers, concentrating on the placement to keep drain holes open. The irregular shape and non water absorbing rocks do keep drain holes working well. They might be at most 1" high off the bottom.
Have tried it with/without in my fabric pots. adding a couple/few pounds of gravel seems to make for a better more stable balanced fabric pot when using a lite airy mix. Since rocks don't absorb water don't think they stop drainage in fabric.
acs1 said:
Be that as it may, the discussion was specifically with regards to the age old myth that adding "Stuff" aids in drainage. It does not. It never has, nor will it at any time in the future, unless said stuff is capable of transporting excess moisture to another dimension. But I'm assuming that you don't have any dark matter in your garden. So, I persist.
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I can understand adding gravel to a container as ballast. OK, that's legit. But, If you have more than one drain hole in a pot, and aren't mooring it in clay, you're going to drain. A single quarter inch hole will drain a pot as well as cloth. Now, the cloth is going to give access to air, and that will be better for evaporation. But that's a different issue. Focus... drainage. PWT
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I'm not sure how the holes can get clogged with "soil". If you are setting on the ground, the soil wicks out the moisture in the PWT. That's a good thing. It's why you want to build your raised beds without an impermeable layer between the growing media, and real earth. (or conversely, why you want an impermeable layer if you're putting a garden in sand) But if the "soil" is the mix in the container, then it's the sponge. It's going to saturate and drain, as physics dictates. You aren't decreasing drainage by (theoretically) restricting flow. As long as you don't create an orifice so small, that it's metering drips, or you don't just eliminate drain holes, altogether, your container will drain. The specific gravity of water, and the surface tension of the media are the deciding factors.
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Maybe I'm a bit dense, but I fail to see how you can clog your container with the very media that you've used inside of it.
I cannot sympathize with your problems. I live in a very hot humid climate, and don't want to lose even an inch of oxygenated root space. In fact, I'd be curious to know how you build or buy your media, because this is the reality on all of my containers - I can run my finger over an inch into that space. The waterings take care of that. No way that I want to put something coarse in the bottom that is eventually going to get it's spaces filled in with media, anyway.
Cool. I was wondering if you might be going to say sand. Anyway, FWIW I think the aggregate before the drain holes thing is to do with molecular adhesion hindering container drainage. For WHATEVER reason, with a layer of aggregate or more porous material at the bottom, one has the entire area of the container circle, to take advantage of, to drain the medium, into the rocks or what have you. There is still molecular adhesion, but it's spread over the whole cross section of the container, vs. 4 little square holes (or what have you) in the other scenario. Then these rocks or whatever drain out the small holes around the edge. Molecular adhesion doesn't stand a chance. But if the growing medium were all the way down to the drainage holes, the combination of the medium and the drainage holes would create a restriction, caused by molecular adhesion.
Come on, now. You can see there is no adhesion, whatsoever. The mix has a weakly bonded boundary layer, that's easily eroded by regular waterings. It's the basic principle of a land slide. Nothing special about this. If your media isn't doing this, you have made a non-structural grade of concrete, and not a plant worthy substrate.
I have yet to ever see a container become "clogged". Like literally, ever. Not saying that it couldn't happen, but there would need to be some pretty special circumstances. I mean, a pin hole leak will sink a boat, the same way as a bullet hole. One might flow faster than the other, but the end result is the same amount of water going through both holes. The only way you stop it, is to introduce a non-porous mass to the point of exit. So, in that vein, I'd say that even though tiny holes will drain even the largest container, the limiting factor would be something like roots plugging up a small exit. Again, this is not something that I've seen. You would have to have impacted roots in a normal size drain hole, and by that time, you're worried about being root bound, not drainage.
The PWT of the media is both an obstacle and a benefit. We need some moisture to stay in the container long enough to be utilized. We don't want so much that all oxygen is displaced.
I have yet to ever see a container become "clogged". Like literally, ever. Not saying that it couldn't happen, but there would need to be some pretty special circumstances. I mean, a pin hole leak will sink a boat, the same way as a bullet hole. One might flow faster than the other, but the end result is the same amount of water going through both holes. The only way you stop it, is to introduce a non-porous mass to the point of exit. So, in that vein, I'd say that even though tiny holes will drain even the largest container, the limiting factor would be something like roots plugging up a small exit. Again, this is not something that I've seen. You would have to have impacted roots in a normal size drain hole, and by that time, you're worried about being root bound, not drainage.
The PWT of the media is both an obstacle and a benefit. We need some moisture to stay in the container long enough to be utilized. We don't want so much that all oxygen is displaced.