March 22--I plan to try gardening in some containers this year and would like some advice on how to be successful, since this is my first try.
-- Jerry Johnson, Park Ridge
There are many different types and styles of containers to choose from for your garden. The pots themselves can be decorative or very simple, so choose what best suits your personal taste and design requirements. The size of the pots you purchase should be in scale with the surrounding landscape. The bigger your garden space, the bigger the container you will need. Small containers sitting by themselves on a large patio or deck will look out of place. Small and shallow containers will dry out more quickly, especially later in the season when the plants are more established. When using small pots in sunny locations, you need to stay on top of your watering. Consider using a mix of different sizes of pots grouped together to add interest and the potential to layer plants from taller to shorter.
Whatever container you choose, it is essential to have a drainage hole or holes in the bottom; otherwise water builds up in the container and will drown your plants. The holes do not need to be large, but there must be enough so that excess water can drain out. If a container has no holes, try drilling some yourself. A container without holes is best used as a cover to hide a plain pot or to grow aquatic plants. Adding gravel at the bottom of a pot will not improve drainage but can add weight to a lightweight container. This is useful in a windy location when more stability is needed.
It is important to use a soil-less growing medium designed for containers -- your local garden center will have bagged growing medium for sale. Do not use 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 badly.
Bags of growing medium are typically sold by cubic feet. 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 (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 used the empty bags my growing medium came in as filler. Styrofoam peanuts will work too, but they create a mess when the time comes to clean out the containers. I like to have a depth of at least a foot 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 container. Gently press the planting mixture as you fill the container. Do not fill the medium to the top of the pot as you will need an inch or so to allow for watering. Use less space for small pots and more space for very large pots. The growing medium should be slightly moist as you are planting.
Tim Johnson is director of horticulture for the Chicago Botanic Garden in Glencoe, ctc-realestate@tribune.com.
If you have plant or gardening questions, contact the Chicago Botanic Garden's Plant Information Service at 847-835-0972.
