My new home has limited space for garden beds and a decent-sized patio for container gardening. Can you provide advice on gardening with containers?
— Scott Kozlowski, LaGrange
Container gardening is a versatile way to soften a patio and gain some growing space. You’ll find many types and styles of containers in the marketplace, from decorative to simple.
Containers should be in scale with the surrounding landscape. The bigger your patio, the bigger the container required. For example, using several small containers on a large patio will look out of place — but they’ll look just fine when combined with larger pots. Also, small and shallow containers will dry out more quickly, especially later in the season when the plants are established and root-bound. When using small pots in sunny locations, I’d recommend paying close attention to watering, especially during hot weather. You may want to consider grouping various-sized pots together to add interest, allowing you to layer plants from taller to shorter.
Before you make plant selections, ensure your containers have drainage holes. If a container doesn’t have holes, try drilling some yourself. Otherwise, a container without holes can be used as a cover to hide a plain pot or for growing aquatic plants.
Adding gravel at the bottom of a pot won’t help with drainage, but it can add weight and stability to a lightweight container. It’s also important to use a soilless growing medium designed for containers — your local garden center will have bagged growing medium for sale. Remember not to use garden soil in your pots. Garden soils used in containers, even when mixed with compost, will generally be slow to drain, causing plants to perform badly.
Estimating how much growing medium to buy can be challenging, as bags are typically sold by cubic feet. To calculate the volume of a square container, multiply length times width times height. For round pots, multiply 3.14 (pi) times the radius of the pot’s diameter times the height of the pot. All units of measurement need to be in feet to give you the number of cubic feet of growing medium to purchase. Convert inches to feet by dividing by 12 (inches per foot). I like to purchase a little extra medium to be sure that I have enough.
If you have large containers and want to save money by using less growing medium, use empty plastic pots turned upside down in the bottom of the container to fill in space. I have also crumpled up the bags that the growing medium and compost are sold in and used those as filler. Styrofoam peanuts will work, but create a mess when it’s time to clean out the containers.
I like to have at least a foot of depth of medium above the filler at the bottom of the pot; use a greater depth if you are planning to grow very large plants or shrubs in your containers. Gently firm the growing medium as you fill the container, leaving space at the top. You’ll need about an inch gap to the top of the pot to make watering easier — use less space for small pots, while more space is better for very large pots. Moisten the growing medium before planting. I hope you enjoy your patio garden this season!
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.
