From the Ground Up

by Derek Burch


I have seen far too many nurseries and garden centers in which the job of watering was given to the new kid, or to someone who had no set job in production or sales.


The implication is that anyone can water - whereas, in fact, it is not a simple job, and done badly will undo all the efforts of the rest of the staff. It is not easy when dealing with a pot in the nursery or greenhouse, and perhaps more difficult when the pot has found its place in someone's home.

Plants need water as a raw material for making simple sugars, in the process called photosynthesis. They use it to carry other things through the plant, either dissolved in the water or carried by the flow, and most of the minerals that the plant obtains from the soil enter the roots in solution. Water also fills out the cells and does much to form the shape of the plant by keeping the cells plump. Almost all of this water has to enter the plant through its roots.

Most of the cells in the roots are alive, making up compounds for various purposes in the plant, breaking down sugars for energy to do this and even passing liquid from one cell to the next in a way that requires energy -although most of the movement is just water drifting from a place where there is a lot, to a place that has less. Each cell needs oxygen to break down the sugars (this process is called respiration), and has carbon dioxide as a waste product which must be disposed of. Both these gases move around the plant dissolved in water.

So, what the plant needs is a good supply of water at its roots. But, because the cells also need oxygen, the water that is taken in must have oxygen dissolved in it. Now, if I may refer back to the previous issue of the magazine, you may remember that we were talking about the soil as being made up of solid bits and the spaces between them. The spaces are filled with air until a liquid forces the air out, and then refill with air as the water drains.The size and shape of the solid particles determine how big the spaces between them are, and this determines how long water can resist the downward pull of gravity and stay in the spaces. The skilled part of making a soil mix (better to call it a "potting medium" since some of them for houseplants do not have any soil) - the skill comes in getting the right combination of space sizes so that some empty quickly after a watering, letting air back in, and some hold water for the roots to use.

Assume that such a mix has been made, what would be the ideal watering regime? Let's deal with the situation for a house plant. Watering in a nursery has a lot more that needs to be discussed, and can wait for another time..

Go to Part B

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