Mother Earth Living

Growing Herbs in Urban Landscapes

By Debra Kirkpatrick
August/September 1994
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The Herbs from Mother Earth

A few herbal lessons from The Urban Herbalist.

People have always valued herbs. For that reason alone, herbs merit inclusion in urban landscapes or anywhere people congregate, meditate, pause, or pass by. They can lend an intimacy and a restful ambience to the hurried and often impersonal atmosphere of cities and suburban developments. Herbs can animate lifeless areas and stimulate the senses with their beauty and fragrance. Many are highly ornamental, especially appreciated for their interesting leaf textures, foliage colors, and softly beautiful flowers.

Opportunities abound for enriching developed areas with herb plant­ings. The traditional geometrical herb garden motif, for example, can be easily translated to many situations within the architectural fabric of a city—restated or reinterpreted in courtyards, townhouse plots, and terraces to create interesting patterns. Residential and public spaces can be enlivened by herbs in street-level plantings, raised beds, window boxes, and containers. Parks and residential properties are excellent settings for naturalized plantings using native herbs, which can be a refreshing alternative to the annuals commonly used for seasonal-interest beds.

Creating suitable growing conditions can be a challenge. Trees and buildings may obstruct direct sunlight. Wind turbulence patterns can dehydrate or batter plants. Paved areas may impede drainage and also limit the availability of moisture. Frost pockets and stagnant air spaces can form in the canyons of the city or even around townhouse courtyards. Chemical pollutants, compaction, and rubble make the soil inhospitable to plants. Severely polluted soils may even need to be replaced. But with careful site analysis, proper plant selection, and adequate soil preparation, herbs will adapt well and become a practical and beautiful landscaping option.

Light

Many popular herbs in American gardens trace their origins to the hot, dry, gravelly slopes of Mediterranean Europe, and these conditions can be approximated in many urban and suburban environments here. A great number of herbs need heat and bright light to thrive, but others do remarkably well in various amounts of shade. Many native woodland herbs perform well even in deep shade. For a list of herbs that prefer or will accept shade, see page 36.

When assessing a site’s light conditions, pay careful attention to obstructions in or near the planting area. Buildings, tree canopies, walls, hedges, and trellises all can affect how much light gets through to the plants. A fine-foliaged tree or a trellised vine with small leaves and an open branching habit will allow more light through than canopies with larger leaves and a denser habit. A building can totally block direct sunlight, but it can also ­reflect light, depending on its texture, color, and surface material. Dark, highly textured surfaces absorb light; smooth, light-colored surfaces are ­better reflectors. Sometimes the patterns of reflected light produce a beautifully subtle effect, but glaring ­reflected light in garden spaces should be avoided.

Because a plant’s health and vigor are influenced by many factors, its adaptability with regard to a given factor depends on all the others. Light, moisture, and temperature are intrinsically related. For example, a plant that receives a little more light than is optimal may perform well if it is watered more frequently. It may do well if the microclimate is cool but may suffer from heat buildup in a heavily paved area. Use a holistic approach to site analysis.

Temperature

The more moderate climates offer more flexibility in design, but even extremes of heat and cold can be tolerated by many herbs with careful planning. The amount and intensity of light reaching a planting site have a direct effect on the temperature. Even in cooler climates, a site that receives full afternoon sun or strong reflected light requires plants that can tolerate heat.

Many herbs, such as the artemisias, santolinas, and rosemaries, prefer hot, dry weather. These plants are excellent choices for hot sites facing south, southwest, or west. They can be especially useful where heat buildup from pavement and buildings knocks out other plants.

Heat retention in soils adjacent to driveways, sidewalks, and streets causes plants to dry out faster than those with more ground area around their roots. Herbs planted in raised beds, containers, and especially window boxes tend to dry out quickly from exposure. Using generously sized containers and beds and insulating the inside of raised containers can moderate temperature extremes while minimizing moisture loss.

Mediterranean herbs such as lavenders, thymes, and savories do not tolerate the combination of heat and high humidity and are susceptible to fungus diseases of the roots and foliage. The wide variety of herbs that do accept heat and humidity includes oreganos, basils, and fennels. The mints tolerate humidity but prefer cool temperatures.

Cold is harder on herbs than heat, and in climates where temperatures drop below freezing, hardiness is an important design con­sideration. Winter protection often enables borderline-hardy herbs to survive in very cold regions. Maintenance should include mulching the soil, using antidesiccant foliar sprays, withholding fertilizer late in the season, water­ing thoroughly before the ground freezes, and avoiding planting in stagnant cold pockets and windy areas. The traditional use of evergreen boughs as mulch material in herb gardens is effective; apply them after the ground freezes.

Herbs planted in containers, raised beds, and window boxes are much more susceptible to winter injury than the same plants would be growing in the natural insulation of the ground. Excessive freezing and thawing are a major cause of injury. For permanent aboveground con­tainers, choose herbs that are rated hardy to one or two zones colder than your own.

In warmer climates, the herb gardener has a tremendous range of plants to choose from. Many hardy annuals continue to grow year round. Rosemary is a valuable landscape plant in the drier regions, used extensively as a ground cover or shrubby evergreen ornamental. Many of the beautiful sages, tender in colder areas, are evergreen in Texas and Florida.

Wind

Wind damages plants by increasing water loss through transpiration. During the growing season, plants in windy spots may need watering twice as often as they would in a sheltered spot. Strong winds can even loosen and uproot plants, particularly newly planted ones.

In a city, gusts can accelerate to high velocities as they funnel through skyscraper corridors. Forceful eddies may swirl around tall buildings and into courtyards. Rooftop gardens, plazas of high buildings, courtyard gardens, and street corridors are particularly vulnerable to wind damage.

A strategically placed wall, hardy hedge, or perhaps an arbor covered with a hardy vine can deflect winds from a planting site. Such a barrier serves as a windbreak, lifting the wind up and over the obstruction. The protected area at the base of the wall or hedge is an excellent location for herbs.

If creating a windbreak is not feasible, you may have to take other measures to protect your plants: using antidesiccant foliar sprays in areas where they are susceptible to winter injury, staking tall herbs such as angelica and fennel, and pruning herbal shrubs and trees to help prevent wind damage.

Soil

Many urban and suburban soils are compacted, acidic, and high in soluble salts. They tend to be dry, depleted of nutrients, and sometimes full of building debris; the topsoil layer may be shallow or absent. Any of these conditions can make growing plants difficult.

Soil analysis at a local county extension office or diagnostic lab can determine whether your soil needs to be amended. Good drainage is essential for growing most herbs. Adding organic matter can do a lot to improve the drainage of urban soils; consult local experts to determine what kind of organic material will best amend your particular soil. If your soil contains hardpan (a very hard substance, often close to the surface, that is caused by interaction of soluble salts or chemicals with the subsoil and is impervious to roots), you may need to replace your soil with fresh topsoil—expensive but invaluable to gardening success.

Because urban soils typically are low in nutrients, adding organic matter is also beneficial from a nutritional standpoint. Herbs grown in beds benefit from two to three applications each year of granular or soluble fertilizer, preferably one with a high phosphorus content such as 15-30-15. Because nutrients are not replenished naturally by plants grown in containers or window boxes, they should be fed regularly with a complete fertilizer.

Moisture

Note the features that affect the moisture your site receives. Buildings, overhangs, and densely canopied trees can significantly reduce the amount of rainfall reaching a plant below. Paving that is sloped into planted areas may send excessive drainage water into the beds; upslope sites will lose water to runoff.

In sites that receive little natural water, plant herbs that are drought tolerant. The chart at right lists some possibilities. Even drought-tolerant plants will need moderate amounts of water until they become established. Water the soil deeply, and mulch to hold moisture in the soil. Trickle irrigation methods are outstanding for water conservation; a simple soaker hose is an inexpensive and effective way to water herbs.

In predominantly paved areas, water runoff from rainfall is much more rapid than it is in open ground. Water penetration into a planting bed or pit in a paved area is often insufficient to maintain plant growth. In addition, the concrete retains heat, which in warm weather can build up and bake the soil. Plants show a marked improvement in size, health, and performance when they are planted in large openings in the pavement with ample common root space instead of singly in individual planting pits.

Thorough, deep watering will leach out potentially damaging soluble salts.

One Garden

The atmosphere you want to create in your urban or suburban garden, as well as the characteristics of the site itself, will determine the lines and shapes that you use. Irregular, free-flowing lines convey a sense of naturalness, informality, and spontaneity; highly defined lines and geometric shapes create a more formal atmosphere, which can be equally suitable to a rich variety of herbs with their lively array of color, texture, and shape. Designing a garden that relates to its environs and fits gracefully into its allotted space takes thought and careful planning, but there are many ways to achieve this.

At left is one example of a design that transforms a common front yard into an attractive entrance courtyard garden. It features a central knot ­garden and border beds of herbs ­enclosed by a dense pri­vacy hedge. This entrance treatment offers a place for people to interact with one another, and functions much as the traditional front porch does.

The simplified version of a geometric knot garden is a good example of the way in which historical precedents can be adapted to meet the needs of contemporary garden design situations. The evergreen hedge creates a dark backdrop to set off the colorful herbs positioned in beds facing the house. Hedges, often used for foundation plantings, can be put to better use on the property perimeter. This arrangement offers excellent views of the garden courtyard from inside the house, and the hedge creates a barrier between the public sidewalk or street and the private residence. One must pass through a gate to enter the private garden domain. These walls of vegetation enclose the entrance, creating an intimate atmosphere and a most enjoyable outdoor room.

Notice that the lines of the hedges, beds, and paving edges are designed to correspond to the lines of the house. Matching the brick paving colors to the building brick also helps integrate the house and garden. The concepts underlying the illustrated entrance court design can be easily adapted to a smaller front yard or a different landscaping situation.


Debra Kirkpatrick is a landscape architect who lives in Dillsburg, Pennsylvania. This article is adapted by permission from her book Using Herbs in the Landscape (Stackpole Books, 1992). She did the research for the book with a grant from The Herb Society of America.


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