When most people think of container gardening, they think that seasonal pots of annuals are their only choice. While annuals do provide more options when it comes to providing color all summer long, avid gardeners know that almost any plant can be grown in a container, provided the plant’s specific cultural requirements are met.
I have successfully grown trees, shrubs and perennials in pots over the years, and on one client’s rooftop I even installed a lush green lawn growing in a series of rectangular containers.
This year I have a newly completed patio, and I’m looking forward to filling some of its space with several large containers.
Visitors to my garden often ask me about my containers, and many are surprised to see trees planted in pots. The truth is that well cared for plants planted in the right location will always look good. Here are a few guidelines to consider if you would like to try something a little different in your pots this year.
First, understand that trees, shrubs and perennial plants in containers are going to have fundamentally different growth habits than annual plants. Annuals typically start the year off as seeds, grow tremendously fast, flower almost nonstop and then die. Trees, shrubs and perennial plants put on a limited amount of new growth, have a period of one to two weeks when they flower, and then spend the rest of the season looking pretty much the same.
These differences in growth habits require differences in care. Annuals in containers benefit from regular feeding during the spring and summer months as they grow and produce flowers. Trees, shrubs and perennials, on the other hand, prefer early spring feeding while they are in active growth and then only light or periodic feeding during the summer months. Overfeeding results in burnt foliage or damage to root systems.
Another point to consider when selecting shrubs or trees for containers is that their root systems grow very quickly and will fill a pot in no time at all. Active new growth above the soil is a function of available root space, adequate water and proper nutrition below the soil. Containers for trees should be on the large size for this reason. Larger pots also prevent root zones from getting too hot during the summer months when temperatures soar.
After growing for several years in the same container, trees and shrubs will either need repotting or will need their roots pruned back and the soil in their pots replaced. A smaller stature tree such as Japanese maple will tend to be more tolerant of life in container than a larger tree such as a Norway maple would.
When I plant trees in containers, I keep them contained for three or four years and then plant them into the ground and start with another tree. Some trees, especially conifers, are more tolerant than others of long-term life in a pot.
Winter care is also a consideration. Keep in mind that a pot sitting above ground will freeze solid, and the trees roots will be close to the same temperature as the surrounding air temperature. For this reason, be sure the tree you select is hardy for your area.
I often plant foliage perennials such as Heuchera or ferns in the same container with trees. Both require similar care, and I prefer the look of foliage rather than bare soil. If your containers are not large enough to accommodate additional plants, you might consider topdressing the soil around the tree with small stones such as rounded river stone for a more finished look.