Here's a guide to buying plant containers.
As a gardener, you have a wide range of choices when it comes to selecting a container for your potted plants. Good drainage and the right size for your plant's root system are the two most important considerations, followed by the container material itself.
When choosing plant containers, pay attention to the weight of the planter if you will need to move it. Of course, don't forget to pay attention to color and shape -- though they're more of an issue for gardeners than plants.
Drainage is essential to virtually every container plant. In fact, more container plants die from overwatering than underwatering. When water fills the air pockets needed for root development, the plant quickly dies. So unless you're growing a containerized water garden, ensure the container you use has a drainage hole. Some come with removable plugs, while others indicate where a hole must be drilled on the bottom of the container.
You may find beautiful pots -- often ceramic or plastic -- that lack a drainage hole. They're sometimes referred to as cachepots. You can still use them, just not to plant directly in. Instead, place your container plant in a slightly smaller container that has a drainage hole. Then, add a small inverted saucer or other item inside the bottom of the cachepot. This elevates the plant, allowing it to sit above excess water that collects in the bottom of the cachepot. Slip the potted plant inside the nondraining container like an arm inside a sleeve and watch to be sure that water doesn't build up above the level of the saucer.
Avoid adding rocks or stones at the bottom of a container, then filling it with soil. This practice, though often advised, won't prevent roots from rotting. Water moves by capillary action -- from large pore spaces in the soil to progressively smaller spaces. Adding stones decreases the capillary action.
Like Goldilocks with her porridge, you want a container-to-plant ratio that is just right. A too-small container cramps root development, while a too-large container looks awkward and holds so much soil that moisture retention may be a problem for a tiny root ball.
In general, use a container that allows plenty of room to accommodate the root system plus room for some growth. It should also allow an inch of room ("headspace") above the soil level for watering.
Visually, the container should be about half the height of your plant (or a third of the total height of the plant plus the container). Using this design principle, a 9-inch pot looks fine with an 18-inch plant, because 18 plus 9 equals 27, and 9 is one-third of 27. This rule applies whether your container holds one plant or several.
Wide, short containers hold water throughout the soil better than narrow, deep containers, which quickly drain water away from the top half. However, both containers have their drawbacks: Wide, short plant containers may cramp deep-rooted plants and stunt root growth, while tall, narrow containers are more likely to tip in the wind.
Containers come in many different kinds of materials. Each has advantages and drawbacks.
Plastic and composite plant containers are lightweight, easy to handle, relatively unbreakable, and easy to clean and store. Many plastic containers tolerate the freeze-thaw cycles of winters in cold climates and can be left filled with soil outdoors year-round without fear of cracking. Because moisture isn't escaping from the plastic, it keeps soil moist longer than terra-cotta. If you are a person who tends to overwater plants, you may want to avoid plastic containers. Also, top-heavy plants may tip over when planted in containers that are too light.
If they are unglazed, terra-cotta containers are porous, allowing air and moisture to travel through the sides of the container. Soil in clay containers dries out faster. This is an advantage for cactus and succulents but means you need to water more frequently for other plants, especially in hot, dry weather. Terra-cotta is breakable and heavier to lift for storage. Clay containers, if left filled with soil, tend to crack during freeze-thaw cycles in cold-climate winters. Because of their heavy weight when filled with soil, they are good choices for top-heavy plants.
Self-watering containers may seem like a dream come true. They're great for office settings where plants may be kept on a routine maintenance schedule. There are several techniques used: pots-inside-pots, wicking systems, or vacuum systems that release water as roots break the vacuum. All self-watering containers keep the soil constantly moist so plants don't dry out between watering. If you are growing plants that need to dry out before the next watering, avoid self-watering planters. If you're not sure, monitor your plants for the first few weeks to be sure the soil doesn't stay too wet.
When it comes to color and shape for your plant containers, use basic design principles. Choose containers by planning where they will be placed. Coordinate outdoor containers in color and shape with the color and style of the home.
Inside, consider wall color and whether the container will be grouped with others holding a variety of plants. You may want to harmonize your indoor garden by using all terra-cotta containers or plastic containers in a variety of coordinating colors.