UNITED STATES—There are probably just as many reasons to not grow plants in containers as there are reasons to justify container gardening. Some potted plants consume less water than they would in the ground, but only because their demand is proportionate to their limited size. They only want more water in the ground because they can grow larger.
The most drought tolerant of plants are actually the least practical for pots or even large containers. They tolerate drought because they efficiently disperse their roots so extensively. Since they can not adequately disperse their roots in pots, they rely on what they can get from a relatively limited volume of soil. However, even if watered generously, many drought tolerant plants simply can not produce enough finely textured roots to absorb enough moisture.
For example, eucalyptus trees want to begin dispersing their roots while very young. If confined, their long and wiry roots simply go around within their limited volume of soil, trying to find a way out. They can develop a few more fibrous roots than they typically would, but probably not enough to compensate for limited root dispersion.
Wild lilac (Ceanothus spp.), flannel bush, manzanita and smoke tree are not only sensitive to confinement, but have difficulty recovering from confinement if put into the ground after their roots have circled too much within a container. Pines and many other conifers are likewise sensitive to confinement, but some types can recover if the binding roots get severed before they go into the ground.
Plants with dense and fibrous roots are more adaptable to containers. Most succulents and common yucca are good choices. Ferns and some grasses also work nicely, but need to be watered rather regularly. Some types of arborvitae and juniper work better than larger coniferous evergreens. Some small bamboos can stay potted, but not larger types.
Annuals, compact perennials and many ground covers that provide color and fill in space around larger plants are naturally adaptable to container gardening, but their need for regular watering can not be denied. There simply is no practical way of combining container gardening and drought tolerance.
Highlight: Smoke Tree
Wispy billows of pinkish or tan blooms through June and July are what the smoke tree, Cotinus coggygria, is named for. It probably should have gotten more recognition for brilliant foliar color in autumn. It reliably turns bright yellow and orange, and if the weather is right, it can turn rich red and even purplish. Until then, the popular modern varieties have either dark purplish or light yellowish foliage. Some of the older plants have slightly bluish green foliage. The nearly circular leaves are about two or three inches long. Yellowish varieties tend to be shortest. Those with purplish or bronze foliage get larger. Old fashioned green plants are the largest, and can get twelve feet tall and broad. Smoke tree can be large shrubbery, or pruned up as small trees. Aggressive pruning in winter promotes better foliar color through spring and summer, but inhibits smoky bloom. Slightly distressed plants have better color in autumn. Plants that are watered too much are likely to succumb to disease within only a few years.
By Tony Tomeo