Willow Glen Resident
Gardening
Squirrel Treat: Tan oaks, sometimes called 'tanbark' oaks, are California natives. These evergreen trees have long, slighty fuzzy, toothed leaves and plump acorns in bristly cups. Their tannin-rich bark was once used in leather-making.
Too much pot will be hazardous to good health ... of eucalypti
By Tony Tomeo
After too many years in a pot, my lemon gum eucalyptus has finally found a place in the garden. It should be happy there, with plenty of warm sunshine and very good drainage. That is, if it recovers from the many years in a pot.
Like many deep-rooted plants, most types of eucalypti are innately susceptible to root problems that result from confinement. Because most are from semi-arid or arid parts of Australia, they prefer to disperse their roots as broadly as possible. Even with regular watering, they are not satisfied with the limited volume inside even a large pot. Consequently, their roots run circles horizontally around the inside of a container, trying to find a way out. These circling roots tend to be more concentrated lower in a container, and particularly around the bottom of the sides of a container.
Eucalypti are not the only type of plant that is unusually sensitive to confinement. Most woody native plants, most coniferous (cone-bearing) trees, and most oaks are also very likely to have problems in containers within only a short time. Except for annuals and many perennials, almost all plants can eventually have some sort of problem if confined long enough.
Circling roots of any plants fill up space within their limited volume of soil, inhibiting drainage and aeration. Once a plant with circling roots is planted in the garden, the roots stop circling and begin dispersing, but become "girdling" roots as they expand and constrict each other. Girdling inhibits vascular function (circulation of nutrients) as well as stability.
Circling roots should therefore be cut vertically during planting. The most concentrated circling roots at the bottom may need to be shredded more aggressively. This disrupts the circling and girdling process, and stimulates normal dispersion of healthy new roots into the surrounding soil.
Unfortunately, plants that are most sensitive to confinement and girdling roots are generally more sensitive to this sort of root pruning. This is why it is so important to plant them before circling roots develop. Oaks and eucalypti actually perform best if planted when very young, before the roots even figure out that they are confined. For example, No. 5 (5-gallon) eucalypti will grow larger than the same type of No. 15 trees planted at the same time, because the larger trees will need some time to recover from confinement. No. 1 eucalypti would actually be best, if only they were available.
The roots of plants that remain potted for many years sometimes escape confinement prematurely through drainage holes. These roots quickly disperse into whatever soil they can reach, as other less fortunate roots inside are abandoned. Cutting these roots to move or even plant an unhappily restrained plant can be very distressful. Plants that have had enough time to become reliant upon the escaped roots at the expense of contained roots can actually be killed.
Palms, yuccas, dracaenas, ferns and bamboo are some of the few plants that do not seem to mind circling roots, or the loss of roots that escaped through drainage holes. Although roots of these plants are susceptible to compaction as they fill a container, they do not expand, so do not constrict each other when they are free to disperse in the garden. Some bamboo actually seems to perform better in the garden as it outgrows circling roots.
Tree of the Week: tan oak
Throughout the Santa Cruz Mountains, the tan oak, Lithocarpus densiflorus, is quite common. In urban landscapes, however, it is very uncommon, planted either by someone who likes natives, or by a squirrel who knows someone who likes natives. The only nurseries that market tan oak are those that specialize in native species.
Tan oak can get very tall in a forest where it is competing with other tall trees for sunlight, but is relatively shorter and fuller in urban landscapes where it has better exposure. Mature urban trees are generally less than 50 feet tall and not much more than half as wide. The smooth gray bark becomes furrowed with age. The stiff, 5-inch long leaves are slightly tomentose (fuzzy). Unfortunately, tan oak happens to be very susceptible to sudden oak death syndrome (SODS).
Listen to Tony Tomeo's 'New Image Garden Report' Friday mornings at 8:10 a.m. on KSCO-1080 AM (or online at www.ksco.com). He can be reached at www.ttomeo@newimagelandscape.com or 408.358.2574.
