Sometimes things get ahead of you and you have to call in the big guns.

One spring, I had a controlled burn in the meadow area. It is a good way to adjust the balance of plants which will thrive. I had a group of 12-year-olds helping me. They were curious as to why we were burning the field. I told them we were doing it "to change the diversity of plant material". They were still very curious about how fire would do that.

Burning is a natural part of the life cycle of a meadow with prairie plants in it. They withstand and rely on burns.

Everyone is familiar with the natural necessity for periodic forest fires. Old plant material that dominates the land is burned off, and new seeds have a chance to assert themselves. For a meadow, a burn can be part of a transition leading ultimately to a forest.

Another way of changing the balance of power in the garden is through the use pattern. You have seen paths through meadows worn down by humans or horses. Usual plants for the meadow, such as golden rod will be slow to re-claim the area. I try to mow paths throught the lower meadow from time to time to make sure that there is a pleasant walk through it.

If you have the space...why not try natural dirt paths through it?

 When considering long-term development of the garden, it is of particular importance to avoid using invasive plant material. It forces you to be ruthless and destructive all of a sudden when you realize that one plant is hogging the space.

A fundamental principle in naturalization is to increase the diversity of plant material used in the landscape. When dealing with smaller landscapes such as urban gardens, you can incorporate perennials, biennials and ground covers.

This would be a movement away from the standard 4,000 square foot lawn which classifies a majority of garden styles.

There are certain selections of trees for example which survive the urban environment better than others. For example, for street trees, linden and honey locust, both non-native, are excellent choices.

I had a call from a city once who asked me to come down and see the trees which surrounded their city hall. They weren't doing very well. The trees were red maples and were planted in both raised and sunken planters. Within the planters were lights which were directed upwards to show off the "beautiful" specimens. The trees were surrounded by concrete. There was an automatic irrigation system installed which could be programmed to supply water whenever it was wanted.

The idea was, I'm sure, well intended. The investment was there but the likelihood of a satisfactory end result was minimal. Red maples are beautiful native trees. They are not however good selections for this type of stressful environment. It is difficult to say whether anything can withstand those types of conditions.

On one extreme, purists in naturalized gardening will insist upon using plant material which is uniquely native to that location.

Along with being extremely difficult to determine what truly is native, there is the problem of finding the material. It also denies us of some truly exquisite exotic, non-invasive ornamentals. For me, naturalized gardening encompasses both native and exotic species.

For example, the HUMAN ELEMENT is exotic, but is really part of a natural garden. As foreign -- and interesting -- as us, exotic PLANTS are part of the naturalized garden.

We have lost touch with what is native. This is not necessarily our fault. We have inherited the earth from those who pioneered the land, removing the native forests to make room for agriculture and urban development. We have just continued with the removal of natural areas to accomodate for our ever-increasing population.

Horticultural specimens which we tend to plant in our gardens are selected for their ornamental characteristics. Most of them are decendents from Eurasia Turkey, China and Europe and were introduced into North America in the 1700s and 1800s.

Plants readily available in a nursery or garden centre are primarily non-native species. They are often grown because of their:

We must consider the value of utilizing native plant material in the landscape. Why?

Native plant material has the capacity to support 10-50 times more local animal and bird species than exotics.

Native plants and animals have evolved not only to survive the climatic conditions of the area, but also have developed a co-dependency on each other

For example: the survival of the Monarch Butterfly depends on being unpalatable to birds -- from toxins ingested from milkweed.

Traditionally butterfly bush (Buddleia) and fuschia -- both exotic -- are used to attract butterflies. Native alternatives would be columbine or butterfly weed (a native milkweed). The butterfly at the right is visiting my garden, to taste one of my butterfly bushes.

We are only just beginning to understand complex relationships such as this. But the matrix of the plant material will support a greater biodiversity when the plants are native.

Some introduced exotics have a tendency to not co-habit well with the natural environment. Some selections may become invasive and others are notoriously difficult to grow because they are pre-disposed to disease and insect damage.

Purple loosestrife is a perfect example of a non-native which has "escaped" from cultivation. It was introduced to North America in the early 1800s and kept a low profile until about 1930. It was first reported in abundance in the early 1930s in wetland areas along the banks of the St. Lawrence River. It seeds prolifically---up to 2.7 million seeds a season from each plant.

In Europe, where it is native it makes up 1 to 4% of the vegetation in it's natural wetland habitat. In problem areas here in Canada it can make up 75% of the vegetation. It is clear that we have something missing in our habitats which can keep loosestrife in check.

There are many opinions about what should be done about loosestrife. In my view the invasion of loosestrife into our wetlands is a mere symptom of a much bigger problem. It is an indication that the balance has been disturbed in some way: changes in the watertable, changes in the grade of the landscape, or changes in the kinds and numbers of co-habitants.

All of these disturb the ecosystem and pre-dispose it to problems.

To a large extent, Mother Nature is tremendously resilient, more so than we give her credit for. In the case of purple loosestrife, the loosestrife is winning.

There are proposals to introduce a non-native parasitic or predaceous weavel which allegedly would only attack loosestrife and to say with such a solution that the problem is behind us. In my view, this is incredibly short-sighted and completely misses the point.

I am uncomfortable with the uncontested endorsement of the introduction of insects en masse. It is impossible for any biologist to truly understand the complex relationships that will be created and be upset.

The Norway Maple has to be one of the most widely-used trees in the urban landscape. It was introduced from continental Europe and was and is a preferred selection for the urban landscape because its mature height is 35-40 feet versus 80 feet or more for the native sugar or red maple, and it thrives in a very diverse range of climatic conditions.

Naturalists are very much opposed to the use of Norway Maple due to its invasion of native woodlots. It is a prolific seeder, has a dense canopy which does not allow for natural succession of a woodlot to take place.