Mid-Atlantic Gardening: Soils, Soil Mixes, and Drainage Issuesby Tapla (Al)., 0 by tapla

tapla wrote:
Just for the sake of argument-----IF a plant is watered carefully, NOT soaked to the bottom, is it possible to avoid having this parched perched water area? Yes, it's possible, and many people use this strategy hoping to minimize the negative effects associated with perched water columns. However, inherent in the strategy are two problems. One is that it's difficult to wet the entire soil mass w/o creating a perched water table in soils that support perched water. This often means dry spots in the soil/root mass that cause localized death of fine roots. Even if it doesn't kill the plant, regenerating new roots to replace those killed by dessication steals energy from the plant, energy that would otherwise have been devoted to new growth, more blooms, fruit ..... Secondly, watering in small sips ensures that all the residual dissolved solids in your tap water and fertilizer solutions remain in the soil. This accumulation of salts makes it increasingly difficult for plants to absorb water and the nutrients dissolved in water, and is substantially to blame for those burned leaf tips and margins that tend to be most noticeable around this time of year when central heating systems are working hard and humidity levels are low. Continually watering in sips will eventually result in sickly plants and cause 'fertilizer burn' even if you never fertilized, or are using only organic sources of nutrients, so it's a practice that should be avoided.

The ideal way to water is to moisten the soil to the point where water is almost ready to exit the drain (takes an educated guess). Let the plant rest for a few minutes, then water again so 15-20% of the total volume of water applied in both waterings exits the drain hole. Your pot should always be lifted above the effluent that drains into the saucer so the salts being flushed from the soil have no way of getting back into it.

A knowledgeable plant person would not pour a quart of water into a 10" pot, as this would "drown"
the plant.Sure they would. Why not? ;-) In the summer time, I regularly apply at least a half gallon of water to my 10" pots, and in the winter time, I'm sure it's always more than a quart. The reason is ..... I can. The soils I make hold little or no perched water, so I can run a gallon of water through a 4" pot every day if I like, and no harm will come to the plant from over-watering. My succulents and cacti can stay outdoors on the growing benched in rain for a week straight w/o me being concerned for root health or root function ...... because my soils are very coarse and well-aerated. If watering carefully, and only when needed, water should not collect in the amounts you are talking about to create this PWL. Is this a logical expectation? We have seen why this approach is less than ideal - perhaps the lesser of two evils, but the lesser of 2 evils is still an evil. ;-) If you gain an understanding of how to put together a soil that will work FOR you, instead of against you, you can A) avoid watering in sips and water copiously every time you water, B) stop worrying about the effects of perched water, and C) remove accumulating salts from your list of things to worry about because you'll be flushing the soil every time you water.

Also--if using clay pots--this (the parched perched water layer) should not ever happen. Right? Not so. The material a pot is made from has no bearing on how much water the soil can/will hold. Using the same soil, the PWT in a plastic pot will be as tall as the PWT in a clay pot. The PWT won't persist as long in the clay pot (vs a plastic or ceramic pot) because the pot walls are gas-permeable and will allow air through from the outside and water vapor out of the soil from the inside. That is the primary reason clay pots are healthier for plants than pots made of materials that are not gas-permeable. Air exchange in the rhizosphere (root zone) is a good thing, as it helps rid sulfurous gases, methane, and CO2 that tend to accumulate in soils - especially poorly aerated soils.

Al