I plan on trying to add some containers to my garden this year and would like some advice on how to be successful.
— Anita Singh, Park Ridge
Containers planted with annuals can add a lot of interest to a garden, and they’re an opportunity to garden as a hobby if you live in an apartment without a yard.
I primarily use simple terracotta containers at home, but there are many different types and styles of containers to choose from for your garden. Terracotta containers do need to be kept inside over the winter, since they’ll absorb water and crack with the freezing and thawing during the cold months if left outside.
Most garden centers should have different containers to choose from. The pots themselves can be decorative or very simple, so choose containers that best suit your taste. The size of the pots you purchase should be in scale with the surrounding landscape. The bigger your garden space is, the bigger the container you’re looking for. For example, small containers sitting by themselves on a large patio or deck will look out of place, but they’ll work just fine when combined with larger pots. Small and shallow containers will dry out more quickly, especially later in the season when the plants are established and rootbound, so when using small pots in sunny locations, you’ll need to water more often, especially during hot weather. Consider using a mix of different sizes of pots grouped together to add interest and the capacity to layer plants from taller to shorter.
The containers need a drainage hole or holes at the bottom, otherwise, water will build up in the containers and drown your plants. The holes don’t need to be large, but you do need enough holes so that excess water can drain out. If a container has no holes, try drilling some yourself. (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 will not improve drainage, but it can add weight to a lightweight container in a windy location if you’re looking for more stability. It’s important to use a soilless growing medium designed for container gardening, and your local garden center will have bagged growing medium for sale. The right growing medium will be very lightweight; I’ve come across bags labeled as potting soil that were very heavy, with a sand, soil and compost mix — good for amending garden soil but not for a container. Avoid using garden soil in your pots. Garden soils used in containers, even when mixed with compost, will generally be slow to drain and poorly aerated, causing plants to perform poorly.
The growing medium for containers is typically sold by cubic feet in bags. Estimate how much you need by calculating the volume of your container. For square pots, 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 measure need to be in feet to give you the amount of cubic feet of growing medium to purchase. Convert inches to feet by dividing by 12. I like to purchase a little extra potting soil 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 at the bottom of the container to fill in space. I’ve also used crumpled-up plastic bags that the growing medium and compost are sold in as filler. Styrofoam peanuts will work, but they create a mess when the time comes to clean out the containers. I like to have at least one foot of growing medium above the filler at the bottom of the pot— or a greater depth if you’re planning to grow very large plants or shrubs in your containers. Gently firm the planter mixture as you fill the container. Don’t fill the pot with medium all the way to the top, since you will 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. The growing medium should be slightly moist as you are planting.
There are plenty of choices for plants to use in your containers. An important first step is choosing plants that prefer the growing conditions present in your garden, like shade versus sun, for starters. I like to mix plants with different heights in my containers, including some that cascade over the rim, to create a layered display. One of the horticulturists at the Garden planted one type of annual per container in a mixed group of containers with great success; he called them mono containers. It goes to show that a simple container planting can be effective and beautiful.
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.