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Container Gardening - Part 2

Container Gardening - Part 2

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Container gardening - the name sounds so specialized. It almost seems there is some secret technique to make it work. In reality, it is amazingly easy. Here are some principles and pointers to make it even easier than that!

A Container is a Container is a Container

It may be trite, but you can use almost anything for a container to grow plants. There are a few basic requirements, though, that make a candidate for "the ultimate designer pot" likely to be more successful.

First is durability. One expects a planter to last. Thus any number of materials are not very suitable because they may quickly decompose, break down, rot out, or generally not hold up. This includes wood as well as many metals. Plastic planters can be degraded by the ultraviolet of sunlight and break down. Even UV resistant plastics seem to just delay the inevitable, but in time the plastic becomes brittle, cracks, and breaks. Perhaps this is all a metaphor for the impermanence of this world. In any case, planters do not last forever, so be prepared to replace them eventually and if you have a valuable jardiniere or Ming dynasty vase, I suggest you keep them in the house and do not recommend using them as planters.

Ceramic does seem to have more lasting qualities, though porous clay can be limited by the white deposit of salts that build up in areas that have much calcium in the water. This happens because when you water your plants, some of the water is absorbed in the porous clay of the pot. When water evaporates, it leaves the salts behind. More water is absorbed into the walls of the pot, and evaporates, leaving behind more salt. Eventually the white deposit builds up on the outside of the pot.

DEFINITION: Capillary action refers to the movement of water in small spaces due to surface tension.

The same thing can happen on the surface of the soil in the pot. Water is added, the plant uses the water, and also some evaporates from the surface of the soil, leaving behind the salts that were dissolved in the water. This can happen over and over, as well as capillary action bringing more water to the surface to evaporate there. Over time, a white crust of salt will build up on the soil surface.

Even before the salts are so visible, they can be damaging. A concentration of salts can burn your plants! This is very often the cause of brown tips or brown margins of the leaves. Water moves from areas of low salt concentration to areas of high salt concentration. That's right, the water may actually leave the roots of your plants or at least be so tightly held by the salty concentration that it is not available to the plants. The result: Water goes out of the leaves but is not taken up by the roots. Or root cells can be killed. This is the underlying mechanism as to why too much fertilizer can burn your plants. The salt concentration pulls out the water.

DEFINITION: Osmosis - the movement of water from areas of low salt concentration to areas of high salt concentration.

Soil (or Soil-less) Mix for Containers

What to fill your planters with is a perennial quandary. Again, the mystery is removed if we just consider the basic aspects of soil:





This seems redundant to say soil is a part of soil, but we are referring to the solid aspects. It anchors the plant and holds it up. It is also the matrix for the other components as well as holding the reserve of nutrients. In terms of containers, one usually does not want it to be too heavy, just out of convenience if the plant needs moving.


Water is of course critical for your plant's survival. A good potting medium should hold plenty of water and yet not become waterlogged.


Air is the critical "mystery" ingredient in any soil mix. Roots need air in order to absorb water. In fact, when people refer to over-watering, what they are really talking about is not enough air at the roots. When the space between soil particles is filled with water, there is no air available - the plants may drown! This is also why the symptoms of over-watering are so much like the symptoms of under-watering. In either case the water simply does not get to the leaves.

Juggling these three ingredients is the key to your happy container plant. And a good soil mix is the key to proper water and air. Next time, we'll get down to the nitty gritty of the soil mix. Until then, happy gardening!

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