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Introduction

The basis of our approach to native gardens is the use of native plant species from local habitats. Since no individual species exists in a vacuum, a  natural extension of this  approach is to base designs on the whole plant community that is local to an area. It turns out that there are very good reasons for doing this

Basing native garden design on local plant communities accords with a rather striking claim. Quoting Burt Wilson, founder of Las Pilitas Native Plant Nursery, "native ecosystems in California are based upon cooperation, not competition. Native plants cooperate with each other, but they compete against alien plants," While the possibility of applying so dynamic an idea to gardening is exciting, questions quickly arise as to what this almost anti-Darwinian-sounding claim really means. To understand the nature of the cooperative relations that hold within a native plant community, we must go underground and look at the relation between native plants and the other organisms that live in the soil.


Plant Community: an Underground View

A common property shared by most local native plants that grow outside of riparian or marsh areas is that they are drought-tolerant; a survival strategy they evolved under the local climatic and soil conditions of our region. This strategy allows the plants to exist under conditions where it is not unusual to go without rain for many months during the hottest time of the year.  In addition to many adaptive mechanisms these plants have developed for preventing water loss (waxy cuticles, smaller leaves, summer dormancy, etc.), the ability of native plants to deal with environmental stress is also due to their relation with fungi that live in the ground and that attach to the plants' roots.

These relations are fascinating given that fungus constitutes a separate kingdom of organisms distinct from plants. From among the many classes within this kingdom it is a subset of those that grow beneath the soil that concern us. These particular fungi colonize the roots of plants and form a biological link between the plants' roots and the soil. The bond between the plant and the fungi is called a mycorrhiza, and the types of fungus which enter into this relation with plants are called mycorrhizal fungi.

The nature of the relationship between native plants and the mycorrhizal fungi which attach to them is symbiotic; it benefits both sides. The fungi, which do not photosynthesize and so cannot make their own food, receive carbohydrates that the plants produce. The fungi in turn help break down matter in the soil into usable nutrients that the plants need and, being better suited than plants' roots to absorbing these nutrients, subsequently "share" them with their partner plants. Thus, mycorrhizae are especially beneficial for the plant partner in nutrient-poor soils, like those which our local native plants inhabit.

In addition, since the network of fungal hyphae (the thread-like shapes which the fungi take underground) constitute a larger surface area than a plant's roots, the fungi capture and store more water than a plant can. This benefits plants greatly in times of stress.  During dry periods the fungi end up sharing this stored water with the plants they are attached to through diffusion. In times of extreme drought, the fungal network can in turn get water from the larger trees whose deeper roots have tapped into the water table. This not only helps the fungi survive but also ends up helping the smaller members of the plant community, since water from a deep water table indirectly becomes available to them if their roots are connected to the fungal network.  Thus, the symbiotic relation that exists between a plant/fungal pairing extends throughout an entire plant community because the fungal grid connects the roots of many different species of plants in that community. Due to the role the fungi play in this process, it can be said that the heart of a plant community lies underground.

The nature of mycorrhizae illuminates the depth of the term plant community. The term in its fullest sense must refer to a "cooperative" community that, in relation to other neighboring communities (fungi, bird, insect, etc.), is part of a self-sustaining ecosystem. A question that remains is how this broader view of plant community and in particular how the mycorrihizal relations underlying this view relates to gardens, to which we turn next.

Gardening by Plant Community

There is a growing number of native garden designers developing approaches that take advantage of the benefits of the symbiotic relation between mycorrhizal fungi and native plants. A basic idea underlying these approaches is that native gardens in which the plants can be supported by a mycorrhizal grid are the strongest candidates for becoming self-sustaining.

These approaches involve a number of simple steps that diverge from traditional garden practices in important ways. The basic difference is that they stop trying to repair nature. Instead of trying to improve the climate by adding large amounts of  water, or repairing the soil with amendments and chemicals, the general idea is to try to encourage natural processes by letting nature take its course.

Such attempts at building sustainability into the garden include two basic principles. The first is to design gardens according to plant community. Thus, plant choices will follow from determining which native plants would naturally occur on the site, taking into account the local climate, soil type, orientation to sun, etc. This gives the best chance of achieving sustainability because it is based on relations that we already know work in nature.

The second principle is to promote conditions that will foster mycorrhizal fungi in the garden. Since the needed fungi are either already in the soil or likely to get there from spores that are in the air, no artificial steps are needed. Thus, promoting mycorrhizae simply requires avoiding practices which interfere with its health. It is here where the differences with traditional practices emerge. We illustrate this with three steps for promoting mycorrhizae: getting rid of weeds, mulch, and avoiding soil additives. 

Weeds

The first step for establishing a successful native garden is to get rid of weeds. While this is analogous to traditional gardening practices, it differs in that weeds, or unwanted/ harmful plants, will be defined a bit more broadly than is usual.

The definition of weeds used here will be all plants whose maintenance interferes with maintaining healthy soil conditions for natives. These will include:

a) Plants that require a lot of water and nutrients for quick growth, and thus are very competitive with native plants for these resources,
b) Plants that typically grow fast and that can crowd out the native plants, which take longer to develop,
c) Plants that do not connect or do not contribute to the mycorrhizal grid, and thus compete for resources without giving anything back to the community, and
d) Plants whose maintenance adversely affects the nature of the soil from the point of view of what benefits the fungal network, and thus the plant community in the long run. 

Thus, from the standpoint of a native garden, the term weed will not only include traditional weeds, but also annual exotic garden plants, many perennial exotics, and lawns, since the maintenance of these alien species moves the nature of the soil away from supporting the fungal species that natives require. In short, the soil conditions which support imported, water-loving garden plants can inhibit the growth of a mycorrhizal fungal network.

Mulch

Once the first step is completed and the weeds are removed, the second step for a native garden is installing mulch. Mulch imitates natural leaf litter that protects plants roots from heat and helps the soil from baking in the sun. Just as importantly it helps stifle the re-emergence of weeds from the seed banks they leave behind in the soil. This practice is in line with traditional approaches to gardening where mulch is recommended, except that here, one of the main concerns is that mulch also helps make the soil more conducive to healthy fungal growth.

No Fertilizers

The third step in this approach to native gardens is to avoid adding anything to the soil that will change its chemistry. This natural approach differs immensely from traditional garden practices that support exotics.  This prohibition against soil additives includes all fertilizers, soil amendments, compost, fungicides (obviously), herbicides, and even insecticides. This prohibition even applies to the kind of over watering practices that many exotic plants require. The reasons for these prohibitions are that: a) both large amounts of water and the use of fertilizers create environments which favor the resurgence of weeds, and b) fertilizing and over-watering can interfere with the health of the mycorrhizal grid by promoting a bacterial-dominant soil. In short, all additives that are typically used to make the soil suitable for exotic garden plants are to be avoided.

Installation

After the removal of weeds and mulching, the basic strategy for installing a native garden is simply to plant, water till the plants are established, and then let nature take its course. This method of gardening obviously wastes fewer resources and pollutes the environment less than normal horticulture practices. In addition, a plant-community-based garden design is especially dynamic because it takes advantage of natural relations between the soil and native plants to allow the garden to become a self-sustaining, cooperative system, as happens in nature.


Questions? Comments? Please feel free to contact us
by e-mail at northparknativeplants@yahoo.com
or by phone at 619-846-0585.
We look forward to hearing from you.

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