By: Colleen Rasmussen
The first question we ask ourselves when we want to start gardening is, “Where shall I put this rose, or tulip, or petunia?” Whatever the plant you are planting, a location is definitely the first thing to consider. Most gardeners choose to plant their plants directly into the ground. On the other hand, greenhouses usually use potting materials.
Being a contentious horticulturalist, we have the ability to choose where the fruits of our labor will be sowed. To some this may be an easy answer, but there are many alternatives to planting directly in the ground and you need to make an intelligent conclusion based on the intentional outcome you want from your planting. A few considerations must be contemplated before your entire stocks of plantings go into the ground.
When the results of your plantings are to sell cut flowers, you would definitely want to plant into the ground. In a greenhouse setting you would want to us the process of planting in pots. There are several reasons that show why this is an excellent choice. When transplanting seedlings, the confinement of the container will allow the rooting medium to be transferred with the plant. This will limit the need for sterilizing the rooting medium. When planted in beds disease, crowding, and stunting becomes a problem. Isolation and removal of diseased plants are easier in containers. (Whitcomb, pg. 38-39)
In a nursery
atmosphere growing in the ground requires plants to be potted up immediately
before selling, which adds an extra step plus more labor. Plus the nursery needs to be situated on
suitable soil. Root disturbance is
minimized when the plant is finally potted up (Mason, pg. 60).
The purpose of this paper was to gather information on the two main types of pots used in greenhouse propagation today. I found it pointed out the good and bad qualities and the advantages and disadvantages of both kinds of pots. I have included facts cited by many authors, also some of their likes and dislikes, dealing with the use of pots in a greenhouse.
Clay and plastic pots both have some good features, and the choice of pots should be based on which one can be used successfully in the specific situation. Clay (unglazed clay) pots are made of a particular soil and fired in kilns during the manufacturing process (Ridels, para. 2). Plastic pots on the other hand are made from recyclable plastic so disposal is environmentally friendly when the pot is not longer usable (unglazed clay pots are fully recyclable as well) (Rindels, para. 3).
Having been used for hundreds of years, traditional clay pots, often called earthenware, red-clay, terra cotta, or unglazed pots, were most common until the availability of plastic pots came into use. During these years many advantages have been realized. Some of the incentive characteristics that clay pots have are the ability to be porous and good aeration. Old timers will use nothing but clay pots, saying that there is a certain amount of air that passes through the clay. Beginners may be interested in both the clay and plastic types. Scientists have proven by experiments that plants can be grown equally well in plastic or clay pots. The kind of pot is your choice for your personal taste.
According to experienced growers, in clay pots the air and water pass through the walls and dries out the soil. Drying soil absorbs extra oxygen, which activates feeding roots, and these roots by their activity keep the earth inside the pot open and in good condition. Having the roots breathe easily, there is less rooting than plastic pots, where excess rooting can cause breakage of the plastic pot.
Being that there is good evaporation from the walls, clay pots are good for those who over-water pots, in that they need less frequent watering. Another thing is that many people over-feed their plants, and clay pots will allow the fertilizer to leech through the sides with the excess water. The green scum or algae, which grows on the clay pots, is always a sign of overfeeding, whereas the plastic pots cannot help itself in this way.
The familiar unglazed pots come in many sizes, from three to twenty-four inches in diameter. Plants can thrive in almost any container provided they are of suitable size for the root systems and have drainage holes. This gives another good aspect of the clay pot, the pieces from broken pots can be saved and put in the bottom of pots for drainage material. Using this method can save material to be used over and over again.
Red-clay pots have a homey attractiveness and can serve you well, being that they are very durable, inexpensive, and readily available. The “raw” look of the new pot will mellow with time, and harmonize with all colors, found in indoor and outdoor settings. Also the natural clay color of the pot may be less obtrusive than the brighter colors of the glazed pots.
The only thing to be sure of is that the plant is planted correctly. In any event, unglazed pots – traditional or contemporary – are an excellent choice. A terra cotta container is an excellent choice for a shaded area where is won’t dry out as quickly as it would in full sun. Also, a terra cotta pot will be heavy; so don’t use it in a spot that’s extremely difficult to reach (Appell pg. 27).
Choose nonporous pots, preferably if plastic, which is generally superior to old-fashioned red-clay pots (in spite of some people who think that old fashioned is best). Most pots now days are made of plastic, and are widely used. Some statistics say that ten times as many plastic pots are used today as clay pots. But contrary to the opening statement of this paragraph, some do not follow this line of thought. They, meaning plastic pots, are not popular with many indoor gardeners.
Whatever your thoughts are, there are many advantages found from the use of plastic pots. Plants in plastic pots require less water than those in clay pots. To grow plats well in a plastic pot, almost half the amount of water should be given, compared to clay pots. Therefore, less watering saves time. For example, a three-inch clay pot may need watering only three to four days. Plastic pots hold water almost twice as long as clay pots. In plastic pots the soil stays evenly moist, and the plant can survive absent minded or absent owners. If you are going to be gone, your plants can be left and survive a weekend in plastic pots, when in a clay pot it may perish. If watering is watched carefully, this is an advantage; if not, plants are harmed by over-watering. Plastic pots have several drainage hold so small that soil does not sift through and no drainage material is needed at the bottom of the pot. These require the least maintenance, because plastic is non-porous and water can’t evaporate through the walls.
The majority of potted plants are now sold in plastic pots, because they are cheaper to produce, stack easily and are durable. Some say that plastic pots are virtually unbreakable, but they should be discarded if cracked (Mason, pg. 58). Plastic trays, used in greenhouses, have the disadvantage of causing root damage to small seedlings in the transplant stage of development (Mason, pg. 60). Also, the fact that they are lightweight for handling and shipping, gives them an advantage over clay pots. Ranging widely in size and shape, they take up less room when growing or shipping.
Fertilizer salts do not discolor plastic pots and salts do not build up on the rims, as they do on clay pots. One advantage of the fact that these salts cannot get through the walls of the pot, it leaves the outsides always clean, and the inside can be wiped cleaned with a sponge. If you put the pot away dirty, you can wash it out with a brush or cloth dipped in hot, soapy water without any scrubbing, and dried immediately for use.
Plastic pots come in colors of green, black, buff, brown, or white – often heavily streaked or mottled. Solid white gray, and soft green pots harmonize with all plants. New plastics are UV stabilized with ultra violet light inhibitors to reduce fading and maintain flexibility which increases the lifespan of outdoor pots (Mason, pg. 58).
To offset all the advantages I have listed, there also are disadvantages, such as clay pots dry out very quickly in high temperatures. So before potting anything in them , they need to be soaked overnight, because dry pots absorb great amounts of moisture from the soil. When soaking, it is better to use rainwater than hard water. For soaking pots that have been sitting number of years in the house, you may need a special solution.
Clay pots “sweat”, lose water faster, and are more likely to develop unsightly deposits. Unless pots are specially treated, they gather moss and fertilizer salts on the outside, which detracts form the appearance of the pot. The pots can be cleaned with a stiff brush and warm soapy water, before potting, and afterwards as needed. The algae, which grow on the outside of the pots, should be cleaned before the pot plant is shipped. If you pick a container made from a porous material like terra cotta, try lining the pot with a layer of newspaper to increase moisture retention (Appell, pg. 26).
Because of the possible presence of disease, it seems desirable to disinfect pots; they may be put in a large kettle and boiled for thirty minutes. Disease can cause leaves or stems to rot if the plant touches the rim of the pot. To prevent this rotting, the rims can be coated with paraffin or covered with aluminum foil, as for African violets.
Clay pots are heavy and particularly if the pot plants are to be shipped, the weight of the pot may be a consideration. Even though the pots are heavy they break easily when hit or dropped.
With those disadvantages of clay pots there are also disadvantages with plastic pots. In the plastic pot, part of the air exchange cycle is broken. Being nonporous, they hold moisture in the soil longer than clay. Then there is a tendency to over-water, particularly when the plant is slow – rooting and loam is on the heavy side. Because excess salts cannot leech out, they will build up to great potency in the pot and damage the feeding roots of the plant, from which it will never recover. Experienced indoor gardeners often lament that apart from much preferring the appearance of the clay, their plants also don’t grow well in plastic pots.
In most plastic pots, the drainage holes are small and all over the bottom of the pot, meaning more dry well material is needed. All pots must have drainage. All pots need to have some sort of drainage material to prevent the vents from being clogged. In clay pots, broken pots are used to cover the drainage hole and allow ventilation.
When soil is moist or wet, the uneven distribution of weight may crack or break the pot at the rim if lifted from one side. Plastic is not suitable for large plants that have a tendency to tip over. When using a hanging basket, the disadvantage is that you cannot plant the sides and bottom of a plastic basket, unless you drill holes that are at least one inch in diameter wherever you want a plant to poke through (Appell, pg. 27).
Plastic pots come in many colors, but the mottled plastic may be distracting to some. Plastic containers are a good choice for a full-sun location, and their lighter weight makes them appropriate for a high spot that might need a ladder for access (Appell, pg. 27). Many people prefer plastic pots to clay.
In doing this paper I feel I have learned a great deal about the use of pots for growing greenhouse or houseplants. Many of these aspects apply in both cases of potted plants. Plants are probably easiest to grow in regular red clay pots. No matter what the pot is made of, it should have a drain hole. Salts will accumulate in the soil if undrained containers because they can’t be flushed out. Personal preference will usually be the major factor determining the type of pot used (Pots, para 1-2).
In my experience with potted plant, I have used both kinds and found these characteristics to be true. I have not as yet formed my opinion as to which I prefer. I like the moisture holding capacity of the plastic pot, but I prefer the old-fashioned color of the clay pots. Maybe as I become more experienced in my field, I will realize the difference between plastic and clay pots, and choose a favorite. I really enjoy working with plants, and know that I will be satisfied in my chosen career, and hope to make the best of it.
Appell, Scott D. The Potted Garden: New Plants and New Approaches for Container Gardens. Brooklyn, New York: Brooklyn Botanic Garden Publications, 2001.
Mason, John. Nursery Management. Australia: Kangaroo Press, 1996.
Pots For House Plants. (March 2002.) Houseplant Care, Tips and Advice. [Two paragraphs.] [Online.] Available at:
Rindels, Sherry. (March 16, 1994.) Selecting A Plant Container. [4 paragraphs.] Department of Horticulture, Iowa State University. [Online.] Available at:
Whitcomb, Carl E. Plant Production In Containers. Stillwater, Oklahoma: Lacebark Publications, 1984.