Marin IJ Articles
January 21, 2008
Barbara J. Euser
Recently I attended a symposium of the Mediterranean Garden Society in Athens, Greece. It was entitled “The Dry Garden: Practice and Philosophy.” One of the keynote speakers, Olivier Filippi, a nursery owner and garden philosopher from the south of France, made a deep impression on me. He and his wife have spent over twenty years collecting plants that grow wild in Mediterranean climates and propagating the plants for sale.
Filippi’s basic premise is that if gardens in Mediterranean climates are planted with appropriately cultivated plants, they should not need any additional watering. What a relief that would be: no more overhead or drip irrigation systems to worry about! No bills for extra water for the garden! Not to mention the boon to the environment if precious water resources could be conserved for human use.
Most of us understand that lawns use a disproportionate amount of water and have reduced or eliminated them. Filippi goes one—or maybe several—steps farther. He says, “The problem in gardens is not drought but rather the lack of knowledge on how to grow drought-resistant plants and on the proper gardening techniques suited to dry gardens.”
In practice, what he advocates could be described as “tough love” for plants. His theory is that to establish a garden that does not require any additional water, the plants in the garden must have roots that grow deep enough to collect water from the ground during our dry summer months. In order to develop those deep roots, plants must be conditioned from the time they are planted as seeds, or propagated as cuttings, to use their energy to develop roots rather than stems, leaves and flowers. This developmental dichotomy is referred to as roots versus shoots. Traditionally, the root to shoot ratio in temperate climates is considered to be 1:1. That is, the size of the root system underneath the ground is equal to the size of the plant above the ground. By contrast, for example, a Cistus plant (Rock Rose), that grows one meter high in the wild may have a root system that is ten meters long.
Filippi’s objective is to grow plants for cultivation that reflect this 10:1 ratio. Plants with roots this deep will be able to make use of water deep in the ground and not require additional summer water.
To develop long, straight roots in new plants, Filippi uses tall, narrow plastic containers with vertical ridges. A pot two inches across the top is ten inches deep. The vertical ridges prevent the spiraling roots so often found in nursery-grown plants. Once this spiral of roots is established—Filippi refers to it as a “chignon,” like the hairstyle—it cannot straighten out. Even after a plant has been planted in a garden for years, its roots will be limited to growing in a tight spiral. As proof of this, Filippi produced a tall yucca plant that had fallen over: its roots were clustered in a tight ball. I recalled my own experience with a rhododendron that died in my garden. When I dug it up, its spiralled root ball looked the same as the day I had removed it from its nursery container and planted it several years before.
Once a young plant has developed straight 10-inch-long roots in its container, it can be planted in the garden, preferably in the fall at the beginning of the rainy season. There, the root to shoot ratio is managed by trimming the plant back as close to the ground as possible for the first year—just as though it had been grazed by goats or deer. This is done so the new plant will spend as much of its energy as possible developing its roots. During its first summer, it should be watered slowly and deeply but infrequently: about seven gallons of water once every two weeks. In very dry circumstances, it could be given three and a half gallons of water once a week. After the first summer, the plant should require no water (in addition to natural rainfall) at all.
What the plant does require is trimming back twice a year. Trimming after flowering will keep the plant from using its energy to produce seeds. By reducing the number of leaves, less water is lost through transpiration.
To obtain plants that can develop deep roots, we need the help of local nurseries and commercial plant growers. Alternatively, gardeners can buy younger plants in smaller pots, before they have a chance to develop spiral roots and become root-bound in containers. Another option is to propagate our own plants for our gardens, using tall, narrow pots. These pots are available from nurseries that focus on native plant restoration. It is no surprise to them that plants that are to survive in the wild need to develop long, straight roots.
Filippi has written a book entitled Pour un jardin sans arrosage, published in 2007 by Actes, Sud France. It is being translated into English. You may also check out his website at http://www.jardin-sec.com. The site is in French. It has lovely photographs taken at his nursery near Beziers, France, and a number of plant lists using Latin names for plants appropriate for use in various sections of the unwatered garden.