Because of gravitational potential water is not distributed evenly throughout containers. The amount of water held by the growth medium becomes greater the deeper the layer of potting soil is in the container. The average amount of water held by a standard commercial growth medium in a 12 inch high nursery container after all drainage has completely stopped is as follows: From the surface down 1.5 inches deep 151 ml of water is commonly held by the medium, from 1.5 to 3 inches deep 156-ml., from 3 to 4.5 inches 168- ml., from 4.5 to 6 inches deep 180-ml,. from 6 to 7.5 inches 199-ml. of water is held by the medium., from 7.5 inches to 9 inches below the surface 229 ml., from. 9 inches deep to the bottom (Perched water table) 261 ml.. The greatest loss of water due to evaporation is, of course, from the top two inches. Therefore, when the top couple inches of potting mix feels rather dry, there is still a lot of water in the tree's root zone. When a grower constantly waters the tree, after feeling the top inch or two, he could easily be over watering. Remember, over watering is the number one killer of containerized citrus. - Millet

So are you saying that I should try to feel even deeper than 2 inches if I can?

He is explaining why we should spend $7 and get a moisture meter.

What about drilling holes into the sides of the container near the bottom. Not big enough ones to let the roots come out, but maybe pencil sized ones to aid in air circulation (drying)??

I've heard though that moisture meters aren't bery accurate. I have one and the soil was still at a "4" after a week

How effective would a water wick be in drawing water from the saturated bottom to the dry surface? Has anyone tried this and, if so, what did you use as a wick?

Citrange, water wicks are a NO-NO! They will often encourage root rot and other root related diseases.

Millet: There will always be ultra-dry pockets of media in the container if you are simply watering from the top down and draining at the same time. Those ultra-dry pockets develop through time and will have difficulty reabsorbing water while there are pockets that will always be over-saturated near the bottom area. this is often common with potting media that contained a lot of peat moss. The best watering approach is to soak and shake the potting media. It can be done by customizing the pot to allow plugging it during watering and soaking, and then have enough size and aeration when draining. Very laborious nonetheless.

I have sinced switched from drip emitters to microsprayers. The spread and flow can be easily adjusted, and this allows enough time for any dried out stubborn media to absorb water. Plus you can direct the microspray away from the trunk, minimizing diseases. The point based drip emitters will often create drainage channels that would drip water straight down without spreading to larger regions of the potting media.

Although I've never tried using a water wick, I would have thought they could reduce problems caused by overwet regions.
Why should they make things worse??

I actually did that on vegetables , citruses and apples. They all suffered with the bottom of the pot making foul stench. I have a special container to facilitate the wick method. Drawback is that the water can remain stagnant in some days when ET demand are low, and you know what that means.

The trees I have that survived the flood were the ones in taller pots.. in spite of setting in water for a couple of days on the garage patio before I noticed they were setting in water.. thankfully I moved them or I would have lost them all as they would have floated down the river..
the larger plants were on the north side of the patio which unfortunate for them was the lower side of the patio where the water pooled..

what survived is doing fantastic!!!!!

I do a soak method (allow the pot to set in a saucer for hr or so) at least once a month to help eliminate dry pockets..
when in the house I fill the bath tub to almost the top of the pots and let them sit for 15 to 30 min..

Good post Millet!!

Gina *BabyBlue*

Water and water management is without a doubt the most difficult part of growing plants in containers, and is the least well understood. The saturated area at the bottom of every container, called the Perched Water Table, is present in every container no matter how tall or wide the container. The Perched Water Table is present even in totally open containers without bottoms. Drain holes in the bottom of the container do not control drainage from a container. The texture and porosity of the growth medium and the depth of the container control drainage. The deeper the container, the longer the drainage column, thus the greater amount of growth medium in the upper portion of the container that is well drained. This is the reason Baby Blues trees in the tall containers survived the flood better than plants growing in shallow containers. When the proper aeration, water holding capacity, nutrition, and water management conditions exist, root growth is very rapid and continues to the bottom of the container. - Millet

Interesting discussion.

I have to disagree with Joe about the wicks.

Wicks can be very useful, assuming that they are wicking water out of the container, not back in. Wicks can effectively increase the height of your container and lower the perched water table. Have you noticed that a pot sitting on the ground are more likely to have tons of roots growing out of the holes than are pots sitting on a shelf? The pots sitting on the ground are effectively "wicked"...that is to say, any contact between the ground and the container medium serves to wick away the PWT. This creates more aerated space for the roots, and off they go, often through the hole and right down into aerated soil.

I did some wick experiments which I posted here some time back, essentially showing that a wick effectively eliminated the PWT from a Promix pot and that a CHC pot had a negligible PWT in the first place.

This idea of an elevated perched water table is the reason that adding gravel in the bottom of a pot actually worsens the drainage in the pot. Because that gravel cannot wick away moisture from the medium, adding gravel elevates the perched water table and reduces the volume of aerated medium available for root growth. This boundary layer is created or defined by differences in the size of the particles in the container medium. A friend of mine quotes a study which showed that a boundary layer is created in a container whenever two layers differ in their particle size by a factor of 2.1 or more. I have no idea how they determined that or how they did the study, but interesting, nonetheless.

Also I would add that the amount of water held in a container not only varies by depth, but also by the porosity of the medium, specifically the microporosity of the medium. (Macropores don't hold water and ultramicropores hold water unavailable to plants.)

Citrange, a wick won't bring water back up to the surface because the capillary action in the wick is not that much greater than the capillary action within the container medium that it can overcome the gravitational pull on the water.

To add to Stressbaby's excellent thread. Micro pores in a growth medium, that is pores with spacing less than 1mm, the water is held so tightly due to cohesion and adhesion, that it is not available to the plant. - Millet