By Deborah Pilkington, NC State Extension Master Gardener^SM volunteer of Durham County

Container gardeners, me included, give a lot of thought to choosing which plants will go into the containers.  But not a lot of thought is given to the containers themselves.  Yet, to have a successful container garden in full sun, shade, or anywhere in between, the choice of pot is as important as the choice of plant.  So, for the next few minutes, we’re going to look at factors that should be considered for container choices, especially in our newly-designated hardiness zone 8. 

Porosity

Some containers, such as the familiar terra cotta (“baked earth” in Italian) are very porous, meaning the pot draws water from the potting media through its walls. Other porous materials include hypertufa, unglazed ceramic, and clay. Because of this, these porous pots may require more frequent watering, something to think about if they are going to be in full sun. Less porous choices would be wood or concrete, and the least porous pots are made of metal, fiberglass, plastic, or glazed ceramic.  That means they are going to help the potting mix conserve water.  

Size

The smaller the pot size, the more frequently it will need to be watered, sometimes more than once a day. A larger container is going to be heavier and less likely to tip over. Larger containers will require less frequent watering but can be a bear to move from location to location…unless you own one of these (see the photo below). And the cost of filling the container with potting mix is also a consideration.

Fragility

If a container is fragile and susceptible to cracking in cold temperatures, it will need to be moved to a sheltered area for winter.  Terra cotta, clay, unglazed ceramic, and hypertufa are all fragile materials. The sturdiest are metal, plastic, concrete and wood.

Heat Holders

Metal containers, and dark-colored containers are heat holders in full sun. They can even be hot to the touch! Potting mix in these containers can rise to well over 100°F. Keeping roots well-watered, unless you are growing cactus, is a must. 

Shape

If you are going to grow a shrub or tree in a container, at some point the plant will need to be lifted from the container to be root pruned—an onerous but necessary task.  So, for shrubs or trees you want to choose a container that is wider at the top (below on the right) rather than narrower (below on the left) to make lifting easier. 

(Left) This container is more narrow at the top and would make it difficult to remove a shrub that had grown in the pot. (Right) In contrast, this pot is wider at the top than the bottom and it would be easier to remove a shrub that had been grown in the pot. (Image credit: Deborah Pilkington)

Drainage

Good drainage is a must in container gardening.  If the container doesn’t have drainage holes, you can add them using a drill and the appropriate drill bit. And to ensure correct drainage, don’t put anything in the bottom of your container but soil mix. Adding gravel or covering the hole with broken terra cotta not only defeats the purpose of ensuring drainage, but it also raises the level of the perched water table, moving the level of saturated soil even higher in the container and closer to the roots.

For gardeners with limited space, especially the newcomers to Durham’s condominiums and apartments with balconies, container gardening can bring some beauty and food to your home.  For urban container gardening inspiration, visit the International Award-Winning Master Gardener^SM Container Demonstration Garden at Cocoa Cinnamon at Foster and Geer streets in Durham.

Resources and Additional Information

Check out the links below to learn more about plant hardiness zones including the history and factors used to determine the hardiness zone of an area. What does this really mean for North Carolina gardeners?

2023 USDA Plant Hardiness Zone Map | USDA Plant Hardiness Zone Map

Gardening Association of North Carolina – 2023 USDA Plant Zone Update (gaonc.org)

AN ILLUSTRATED HISTORY OF AMERICA’S PLANT HARDINESS ZONES (With a Closing Look at North Carolina) | by Tom Packer

For more information on perched water tables and soilless media check out the below online guide about drainage for containers.

How to Improve Drainage in Plant Pots, The Proper Way to Do It! – Deep Green Permaculture

If you want to take a deep dive into the physics of water movement in soilless media and media components, visit the following links.

Growing Media (Potting Soil) for Containers | University of Maryland Extension (umd.edu)

Homemade Potting Media (psu.edu) — How to make your own potting media

Learn more about choosing pots with the in-depth article below.

Containers, Pots, and Planters: What Material Is Best? (gardenerspath.com)–

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