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Pesticide-free gardening

Flowery brook.
Photo: Jardin botanique de Montréal (Michel Tremblay)
Pesticide-free gardening

The golden rules for “green” gardening

People used to think that the best way to control insect pests, diseases and weeds in their gardens was with regular applications of pesticides. Over the years, though, it became obvious that this was not viable in the long term, because it upset the ecological balance and endangered people's health. Now the emphasis is on adapting our gardening methods so that we can grow strong, healthy plants able to resist different types of stress.

In fact, the best way to avoid problems in your garden is to start out with resistant plants that suit your site, and to look after them properly. This means using pesticides only as a last resort, when all other methods have failed.

Here are twelve rules for an attractive pesticide-free garden.

1.  Put the right plant in the right place

A plant that needs shade and moist soil will be much more susceptible to insect pests and diseases if you plant it in dry soil in full sun. That's why it's important to choose the right plants for your growing conditions.

In most cases, you are best to move a plant that is obviously in the wrong place than to try to keep it healthy by using pesticides.

2. Choose insect- and disease-resistant plants

Even given excellent growing conditions, some plants are especially susceptible to insect pests and diseases.

Unless you are prepared to devote a lot of time and energy to keeping them attractive and healthy, the best solution is to replace them with stronger plants. This doesn't necessarily mean that you can't grow your favourite plants. You'll find that nurseries sell resistant cultivars for most types of plants: phlox and bee balms that are less mildew-prone, flowering crabapples better able to withstand rust, roses that aren't bothered by black spot, etc.

3.  Create a diversified habitat

In a natural ecosystem, there are a wide variety of organisms that depend on each other. It is a diversified setting where populations of prey and predators tend to keep each other in balance. For instance, the aphids that attack a honeysuckle are gobbled up by ladybird beetles, which in turn are eaten by birds.

All you have to do to reproduce these natural relationships is to plant several different families, genera and species of plants that will attract large numbers of living organisms. The important thing is not to choose just one kind of plant. For a hedge, you will have more success with different shrubs than a wall of white cedar. And a bed filled with shrubs, perennials and bulbs is much better than a rose garden.

If you have the space and you would like some shade, then plan to have different levels of plants. A few trees in your yard, underplanted with shrubs and shade-loving perennials, will provide some pleasant shade and welcome all sorts of living organisms.

4.  Attract natural predators

Flowering plants that produce nectar, pollen and fruit are a good source of food for natural predators (insects, mites, birds, etc.) that feed or are parasitic on harmful organisms. Various plants that attract beneficial insects belong to the carrot (Apiaceae), mustard (Brassicaceae), mint (Lamiaceae) and daisy (Asteraceae) families. Many of them would look good in a home garden.

Also, plan to have some plants in bloom at all times and include some perennials, trees and shrubs that produce seeds and fruit to attract birds. Don't forget to add a few conifers where wildlife can take shelter in winter.

5.  Amend your soil with compost

With the exception of those that thrive in poor soil, most plants can benefit from the addition of compost. Compost makes an ideal soil amendment and fertilizer for your garden: it adds micro-organisms to the soil and provides them with food and shelter, in addition to improving the soil's structure, balancing its pH and adding nutrients that plants need in order to grow.

Because these nutrients are released gradually, plants have a constant, steady source of food. Moreover, there is growing evidence that plants fed with compost are less susceptible to diseases.

6.  Use natural fertilizers

For a “green” garden, you should use natural fertilizers along with compost. Since such organic (plant or animal waste) or mineral (rock powders) fertilizers have not been chemically processed, most of them have to be broken down by organisms in the soil before they can release their nutrients.

This means that in addition to feeding the plants, they encourage biological activity in the soil. Another advantage is that there is less risk of leaching and burning plants roots.

It is best to use natural fertilizers in the following circumstances:

  • when soil test results show a mineral deficiency
  • to pep up a plant that has suffered considerable stress from disease, insect pests, drought, overpruning, transplanting, etc.
  • for plants grown in pots or containers

7. Use plenty of mulch

Mulch will keep the soil cool and moist in summer, cut down on weeds and improve the soil's ability to retain water and nutrients as the mulch decomposes.

It is a good idea to mulch around trees, shrubs and perennials.

Alpine plants and groundcovers requiring well-drained soil could rot under a thick layer of organic mulch, however. It is best to use pea gravel as mulch around this type of plants.

8. Water deeply during extended droughts

New plants must not be allowed to dry out before they are fully established. Once well established, however, most do just fine with natural rainfall. In fact, a plant that is well suited to its growing conditions should not need to be watered unless there is an extended drought.

Plants that do need watering should be watered deeply. Try to avoid wetting the foliage so as not to encourage fungal diseases.

9. Prune trees and shrubs properly

The main reason to prune trees and shrubs is to keep them healthy. Dead, diseased and damaged branches should be removed as quickly as possible.

It is also a good idea to prune overly bushy branches on trees and shrubs in order to give them more air and light, making them less susceptible to insect pests and diseases.

To have more information, refer to our leaflet on pruning ornamental trees and shrubs.

10. Eliminate sources of infestation

You can prevent or at least minimize some problems by eliminating all sources of infestation. For instance:

  • disinfect your toolls regularly to get rid of bacteria, viruses and fungal spores and prevent them from spreading between plants
  • gather up and destroy all diseased or insect-infested plant litter
  • remove weeds before they go to seed

11. Keep an eye on your plants

No matter how well you maintain your garden, problems can still arise. That's why it is important to watch for anything unusual on your plants, including chewed, stained or discoloured leaves, misshapen shoots and galls or discoloured spots on branches.

If you identify symptoms caused by insect pests, a disease or poor growing conditions at the start, you can address the problem before it gets out of hand. The majority of “green” methods are most effective when used early on.

Finally, the more you know about your plants' individual needs and the problems that could affect them, the better equipped you will be to act quickly.

12. Use low-impact pesticides as a last resort

What should you do if one of your plants looks sick? Start by examining it closely to properly identify the cause of the problem. If you don't see any particular insect pests or diseases, make sure that the plant isn't just suffering from inadequate growing conditions (insufficient light or water, nutrient deficiency, overfertilizing, pH too high or too low, frost or wind damage, etc.). If an insect pest or disease is to blame, first assess the scope of the problem and decide whether you actually need to do something about it. Given the right growing conditions, strong plants can withstand a few insects or pathogens.

If you decide to act, start by using cultural, physical, mechanical and biological methods. If you're not satisfied with the results and you decide that you have to use pesticides, choose ones with a low impact. They are not very toxic in the short or long term for human health and the environment. They break down quickly and most of them destroy harmful organisms without interfering much with useful organisms.

Read and follow the instructions on the label before getting started. Pay careful attention to dosages, application methods, safety instructions and treatment intervals. Finally, keep an eye on the plant afterward and adjust your cultural methods accordingly.

Pesticide usage is governed by the Pest Management Regulatory Agency (federal), the Pesticides Management Code (provincial) and municipal by-laws, including City of Montréal By-law 04-041 on the use of pesticides. Check with your municipality before using any product.

To learn more about ecological gardening, attend classes and workshops (offered in French only) on ecological gardening offered by the Friends of the Botanical Garden.

Downloadable documents

Recovering rainwater[PDF - 2.83 MB - 2 pages]

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