Horticulture Principles and Practices

Containers come in all shapes and sizes. In effect, any receptacle may be used to
grow plants, provided adequate provision is made for drainage and the container is
convenient to use. Pots are also chosen to complement the design of the room.
Container Materials
There are two basic materials used in making horticultural pots. Each has advantages and
disadvantages.
Clay Clay (or earthenware) used to be the industry standard for pots but has been
replaced with newly developed material. Clay, being a natural material, “breathes,” or is
porous, allowing water to evaporate from its surface. As such, it reduces the danger of
waterlogging from overwatering. Clay pots are heavier, more sturdy, and able to support
large plants without toppling over (Figure 11–19). However, clay pots are also bulky to
handle and breakable, requiring care in handling. Because it is capable of absorbing mineral
salts and water from the medium, the surfaces of clay pots often show unsightly
whitish marks from salt deposits. During repotting or topdressing, these marks should be
scrubbed off by using household bleach and then rinsed in vinegar. Such marks are not
associated with glazed clay pots.
Pot-bound root growth occurs more rapidly in plants grown in clay pots than those
in plastic pots because the porosity of clay allows air to reach plant roots more readily
than those in plastic (where air is obtained from the open top only). Roots thus tend to
grow rapidly toward the wall of the pot where, upon meeting the obstacle, they begin to
circle around on the surface of the wall.
Plastic Plastic pots are very popular today and are available in a wide range of colors,
thickness, durability, shapes, and sizes (Figure 11–20). Plastic pots are generally less
breakable than clay pots. Even though molded polystyrene pots are used in some situations,
hard plastics are most common because they are lightweight and easy to handle.
Plant roots grow more evenly in a plastic container. One problem with this synthetic
material is that it is not porous and thus plants grown in plastic pots are prone to waterlogging
because they lack the ability to absorb moisture and lose it through evaporation.
Although overwatering plastic-potted plants may be a problem in winter when drying is
slow, plastic pots are advantageous in summer when water stress is most common.
Plastic pots are intolerant of the high temperatures needed for sterilization and thus
are best sterilized by using chemicals. Pots may be soaked for about ten minutes in a
commercial disinfectant solution (e.g., Floralife or Green-Shield), rinsed in water, and
then air dried. This chemical sterilization is not as effective as steam sterilization. For
better results, plastic pots should be washed to remove all dirt before being treated with
chemicals. Plastic pots are also readily toppled when plants grow larger.
FIGURE 11–19 Clay pots. (Source: George Acquaah) FIGURE 11–20 Plastic pots. (Source: George Acquaah)
376 Chapter 11 Growing Houseplants