I purchased some pots, potting soil, and plants from Orchard Supply and have noticed that when I water, it drains very fast and comes out of the bottom of the pot. I have also added draining rock on all my pots.
The most likely problem is that the soil ball is not moist. Place the pot in a bucket/sink and fill half full, or more with water. The pot will more than likely float which mean the root ball/potting soil is not holding maximum water. When the pot sinks let is soak for half hour, remove and allow to drain. If you have the problem again, repeat the procedure.
That could be, but it also could be you have a sharp draining medium. I sometimes order that type of mix specifically when transplanting certain stock needing exceptional drainage. One is a coir based mix, as opposed to peat.
Take out the draining rock, in small containers it actually impedes drainage by causing the water to back up when it hits the different texture of the rock layer.
In big planters with wide flat bottoms a rock layer is used to move the water sideways to the drain holes or slits. It still backs up before hitting the rock layer, but in such a situation getting it out of the bottom of the planter after it saturates the bottom of the soil column and then rushes through the rock layer becomes the priority.
Gravity forces water down between the soil particles, like any other molecule, and is stopped ,held back, by impermeable material. The last time I checked, rocks of any size are much more permeable than potting soil.
Technically, the flow of water is slowed down when there is an abrupt change in pore size. This is counter-intuitive initially, but it is true. A layer of rock beneath finer soil will slow down the downwards flow of water, as the finer soil has a stronger "hold" onto the water than the rock does (due to its finer particle size, I believe). When there is enough water, the gravitation pull will eventually overcome the hold that the finer soil has on the water and will pull it through the rock.
The water "held" by the soil particles is do to the polarity of the molecules and is called hydgroscopic water. This is the water that is used by the plants. The water that is not "held" to the soil is called gravitational water and CAN NOT be held to the soil particles in any fashion, thus "falling" through the soil. This procedure dose not have anything to do with "... an abrupt change in pore size." going from smaller to larger although, as I previously stated, does occur going from larger to smaller pore sizes.
Hydroscopic water is held tightly to the soil particles and is not the water available for plant use. The plant available water is made up of the water content of the soil between the Field capacity (when free drainage has stopped) and the wilting point (when all that is left is hydroscopic water).
Going from smaller from larger does slow down the downward movement of water. Refer to the article linked below and the images on page 3 of the .pdf (p. 25 in the article).
Quote and image below both from the article linked.
"Any change in soil porosity encountered by a wetting front affects water movement... the relatively small number of contacts between the aggregates limits the amount of water that actually moves through this layer. Only when the soil is nearly saturated does the water move rapidly through."
"Water Movement in Soils by Dr. Walter H. Gardner"
>Only when the soil is nearly saturated does the water move rapidly throughand rushes out the drain hole, producing the false impression of enhanced drainage being given by the use of the so-called drainage layer in the bottom of the pot.
I didn't find anyone addressing when the water runs straight through the soil in the pot because the soil won't hold it. IÂm looking for help how to augment our soil in our containers. Our soil doesnÂt seem to retain any moisture so IÂm watering daily and my plants (dahlias, cannas, elephant ears) are wilting and peaked. My dahlias, especially, are losing leaves (yellowing and drying) at bottom of stalk and havenÂt gained any height in 3-4 weeks. We were excited how voraciously everything was growing and expected to see blooms a lot earlier (we had been planting tubers in early May in years past, but started them all in early April this year). ItÂs only the beginning of July, but weÂve had a hellish month of hot, hot, hot days and little to no rain through June here in the Baltimore area.
Is there anything we can add to the established pots (plants are on an average 24-36" high) without emptying the pots completely? If it is too late for this yearÂs blooms, what should we add this fall when we empty the pots into the compost pile (yes, to be reused next year)?