I have been researching container potting media for and have come across the concept of the perched water table (PWT). This is the level in the pot at which the fall in water due to gravity equilibrates with the rise in water from capillary action within the medium.

Some people recommend the use of a wick in the bottom of a pot to lower the PWT and reduce the chances of root rot. It seems reasonable, though not always practical, since I guess you have to get the wick into a dependent position for it to work.

Does anyone use a wick with containerized citrus? Does the use of CHC as a main ingredient in citrus potting media effectively lower the PWT to the point where a wick is not necessary?

TIA, Robert

Robert, I am not certain I completely understand the basics of perched Water Table (PWT). My initial reaction would be to avoid an area that would wick water up into the lower part of the container. Whether by wick or capilery action. The two main ingredients that a good citrus container soil should provide are water and air. Your idea for CHC is great becauce of the large amount of water CHC's can hold (7 times their weight) and at the same time provide of excellent aeration. I don't know about the use of a wick, as I have never used them, nor do I know anyone who has. I do know that growers who have used the constant watering resivoir type of containers experienced trouble. When a citrus tree is planted in the ground, the best method is to dig a hole only the size of the tree's root ball, to be sure to avoid any type of a pool or "lake" beneath or near the root zone. However, I would be interested in reading further about the advantages of PWT. If you could give us some references, it would be appreciated. BTW, welcome to the "Citrus Growers" forum you are centainly most welcome and needed here. I hope you will feel free to discuess anything citrus. There are few rules here. Take care. - Millet

Hi Millet and others,

http://oregonstate.edu/dept/nursery-weeds/feature_articles/physical_properties/physical_properties.html

http://forums2.gardenweb.com/forums/load/contain/msg031557203792.html

Here are two links describing the PWT idea. The taller the container, the lower the PWT. A wick serves to effectively make the container deeper. The wick isn't intended to draw water up, it's intended to draw water out, effectively lowering the PWT and improving aeration.

Maybe I'll set up some Promix and CHC containers without plants and test this. Robert

Robert, see I told you I did not know much about PWT. I thought it added water, instead of reducing water. Sounds promising. Thanks for the links. I'll read them. - Millet

Plants could easily have root rot in this kind of configuration. With nutrients in the solution and some tiny organic matter falling into it, it provides perfect habitat for some pathogens. I used it on apple and it became sickly. The solution may still need forced aeration, just like you would do in hydroponics for it to work well. Unless you can put anti-microrbial chemicals that are not harmful to your citrus, then this could work. Some things doesn't really work as well as those of pictures in the ad when it is your turn to do it.

Joe, I think we are talking about two different things. There is no "solution" in this wick system. Again, it is not designed to draw anything into the container, it is designed to draw water out of the container and reduce the PWT, improve aeration and reduce root rot. The only solution involved here is the water you would normally use on the container.

I set up my little experiment yesterday, so I should have some results to report this morning. I set up four 1 gallon pots, two with Promix (standard potting soil out of the bag) and two with CHC:peat 4:1.5 ratio. I'll measure the difference in weight between the pot saturated just after watering and the weight 16 hours later, with and without a wick, in each growing media. The difference between the decrease in weight without a wick and the decrease in weight with a wick should represent the amount of water the wick effectively removed from the PWT.

The guess is that the wick will remove some water from each growing media. The larger particle size in the CHC medium will result in decreased overall adhesive attraction to water, better drainage, a lower PWT, and therefore less effect from the wick. I sound like a kid at the science fair...

Here are my results. For the saturated figure (weight immediately after watering), I averaged two measurements.

Promix without wick
Saturated 1458g
16 hours later 1318g
Drainage 140g (140ml)

Promix with wick
Saturated 1525g
16 hours later 1322g
Drainage 203g (203ml)

Therefore the wick effectively removed 63ml of water from the PWT of a 1 gallon pot in 16 hours.

CHC without wick
Saturated 1183g
16 hours later 1068g
Drainage 115g (115ml)

CHC with wick
Saturated 1109g
16 hours later 992g
Drainage 117g (117ml)

The wick had virtually no effect on the CHC. Presumable this is because the larger particle size in the CHC lowers the PWT to a negligible level. This may help to explain the success of CHC (or pine bark or other similar media) in containers.

So where might one use a wick? My answer would be in containers with high PWT relative to the propensity of the plant to develop root rot. Containers with old, broken down, compacted growing media, where repotted was not feasible, might be candidates for a wick.

Any thoughts?
Robert

Robert, to get a equal comparison, I converted your results to a precentage. On test #1 (potting soil) after 16 hours the unwicked container still retained 90.4% of the applied irrigation water. The container that was wicked retained 86.7% of the applied irrigation water. The difference was 3.7% less water in the wicked container. Or another way to look at it, the wicked container had 3.7% more aeration in the soil after 16 hours. As the difference was less than 5%, I think you would have to run the test at least three different times to obtain a reliable stattistic. The CHC results are just about what I would think, as CHC's hold the vast majority of the absorbed water in the internal portion of the chip, and not on the outside layer as bark does. Interesting. - Millet

Let me add two more numbers and see if it changes your thinking.

Dry weight of the Promix without wick = 680g
Dry weight of the Promix with wick = 710g

Therefore, the Promix without wick held 1458-680=778ml water saturated, and after 16 hours it held 1458-680-140=638ml water; 638/778=82% of the original water remained.

Promix with wick held 1525-710=815ml water saturated, and after 16 hours it held 1525-710-203=612ml water; 612/815=75% of the water remained.

I couldn't do dry weights for the CHC because mine CHC come in brick form!

Anyway, it is something to think about...another tool in the toolbox, so to speak.

Here are a few other links discussing container plants and media.

http://edis.ifas.ufl.edu/CN004
http://edis.ifas.ufl.edu/CN004

Based on what I have read, and my own experience, I doubt the wick system (as in a wick that serves to promote drainage) offers much in the way reducing water saturation. Of course we are all about experimenting, and it is certainly good to consider all ideas. I suspect the best practices for water management remain.

- Correct pot sizing
- Careful media selection
- Proper watering



Ned