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Window boxes are helpful for homes, fun for flowers
By Tony Tomeo
A long time ago, the people of Venice, Italy, learned the mosquitoes that were so prolific in their city were vectors for several diseases. However, the only materials available to keep them out were either very expensive or restrictive to air circulation. Consequently, window boxes were invented to contain plant species that were repellent to mosquitoes. Although mosquitoes are attracted to their hosts by carbon dioxide, which is exhaled during respiration, many can be deterred by pungent or aromatic plants that are not nearly so offensive to people.
At that time, Italian botanical and horticultural technology was second only to that of Japan, and plant species were being imported from all parts of the known world. Because there were various aromatic plants to choose from, horticulturists could select those best suited to window boxes because of their pendulous growth. For example, previously available species such as lavender or common rosemary could be replaced by trailing rosemary, ivy geranium or nasturtium--which, incidentally, translates from Latin to "nose twister," probably referring to its spicy smell.
Although ivy geranium was probably one of the most effective repellents, plants like rosemary and nasturtium encouraged many to grow fresh herbs outside their kitchen window. Of course, planter boxes evolved into more ornamental and less functional features as more plant species and insect screens became available. As on canals, planter boxes are still useful for windows facing areas that cannot be landscaped, such as driveways.
Plants are always happier in the ground than in containers, so it seems obvious that potting soil should resemble endemic soil as closely as possible. However, the limited soil volume of containers makes good drainage essential. Roots of most plant species would quickly rot in heavy clay soil. Because good drainage allows water to pass through the soil very quickly, materials with good water retention qualities are also necessary components of potting soil. For annuals and perennials most commonly planted in containers, pre-mixed potting soil is ideal. Contrary to popular belief, peat moss does not need to be added and may even hold too much moisture for most plants.
Because containers are exposed to the elements on the outside, they should be composed of materials that insulate the interior soil from extremes of temperature or heat absorbed from sun exposure. Plants also prefer materials that are porous and hold moisture like the soil does. Clay and wood are ideal and "feel" like materials that roots would normally encounter growing in the ground.
Plastic is not bad for roots, but will transfer heat from the sun directly to roots. Plastic pots are also more likely to freeze in cold weather. Insulation of plastic pots can be as simple as placing the pots in baskets or other more ornamental pots. If the plants in the pots cascade over and cover the outside of the pot, no other insulation is necessary. When choosing plastic pots that will be used in exposed locations, remember that lighter colors reflect more sunlight than darker colors. The black vinyl cans used in nurseries work well in nursery production because sunlight only reaches the cans around the edges of the crops. However, these cans are not recommended for gardens where they will be exposed.
Most of the old window boxes built into older homes are wooden and well-designed for the benefit of the plants, but because they are prone to wood rot, few have survived. When installing new window boxes, it important to suspend them slightly away from the wall, leaving a gap that rot or termites are not likely to spread across. If modern plastic boxes are used in exposed areas, plants should be planted away from the outer edge until pendulous plants can hang over to protect roots from sun exposure. Because planter boxes are in direct proximity to walls, they are normally adequately shaded by eaves, or even the upper part of the walls. Window boxes may also be used to hold potted plants.
There are many species suitable for planters, but those used in front of windows should be low enough not to block the windows. Some of my favorites include trailing rosemary, nasturtiums and ivy geraniums. One of my colleagues in the Los Angeles area tells me that Balkan ivy geraniums are currently very popular and an excellent choice for a dramatic, profuse show. (He thinks they are called Balkan geraniums because they look so good hanging from "balkanies".)
Flower of the Week: Ivy Geranium
Certainly not a favorite among horticulturists, ivy geranium, Pelargonium peltatum, is so easy to grow that many consider it a weed. The color range is greater than that of the zonal geraniums: in variations of light pink, red, rosy red, salmon orange, purplish pink and bright pink. They are excellent hanging from pots, planter boxes or balkanies. They are very tough and quickly recover from most abuse, even winter freezing or summer drying. In fact, they perform better if sheared annually in late winter. Although they grow well without any attention, blooms are more profuse with fertilization. Most of the varieties found in garden centers perform well, but more obscure varieties can be found in better retail nurseries. The more obscure varieties usually do not grow as vigorously, but are grown for their more interesting flowers, which can be bi-colored or double flowered. Ivy geraniums are easily propagated from cuttings, which, unlike most cuttings, should be left out for a day or more to allow the ends to dry; this inhibits rot.
Horticulturist Tony Tomeo can be reached at 358-2574.
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Willow Glen, California Since 1992
