Create a Healthy Garden Ecosystem Using Native Plants
If I say that having insects in your garden is a good thing, many of you might think I’m crazy. However there is a lot of research backing up this claim. When you have an insect problem in your garden it is the result of an unbalanced ecosystem. The insect population in each place is made up of multiple levels. You have insect herbivores that will eat plants, the insect predators, and the vertebrates like birds and mammals that eat the insects. It sounds counter intuitive to say that one should take insect herbivores into consideration when choosing your plants. Insect herbivores are however a very important part of a healthy ecosystem. They are responsible for allowing plant energy to be consumed by vertebrate animals. Many vertebrates don’t have the digestive system required to digest plant material. That leaves a lot of energy unavailable. The insects that eat plants make it much easier for many animals to get the energy and nutrients they need.
How do you choose plants that insect herbivores will use? That depends on where you live. Ultimately the answer is native plant species. Native plants and native insects evolved together. Native insects can really only survive on native plants or plants very closely related to the native. The fact that these two groups evolved together helps keeps both the plants and the insects in check.
The next question you might have is ‘Why do I want my plants to get eaten up by insects?’. Well that is a good question. The answer is that if you refrain from using pesticides in your garden and plant native plants the damage that the insect herbivores will so will be negligible or at most barely noticeable. When you refrain from using pesticides you are allowing the insect ecosystem to become more complex. The more complex the ecosystem the more balanced it will be. Adding complexity just means having more trophic or food levels in your ecosystem. Allowing your garden to regulate itself naturally using the native insect predators that evolved along with the native insect herbivores. Many of the pest insects that we commonly think about (aphids, caterpillars, scales, etc.) can be kept down by insect predators. These predators include parasitic wasps, lady bugs, lady bird beetles, lacewings, and praying mantis. The predators will keep the population of insect herbivores at a level where they won’t be doing noticeable damage to your garden.
Native plants are also good for birds and herbivorous vertebrates. The fruits provided by native plants are what the birds and mammals are used to eating.
Why is it a problem to plant alien species in your garden? It can be a problem for many reasons. The first is that the insects that are native to your area won’t be able to use the plant as food. This includes native butterflies. Caterpillars are very specific on which plants they can develop. If you want to have native butterflies in your garden native plants are the only way to go.
Another reason you should not plant alien plants is that they evolved under different conditions and with different plants. The native plants in your area did not evolve a way to compete with the alien species. Often the alien escapes your garden and begins to displace the native vegetation in wild areas. This causes a problem in the ecosystem and throws it out of balance. Herbivorous insect generalists are can survive on many different types of plants. An example of an herbivorous generalist would be the grasshopper. Now you have less native vegetation to feed your complex insect ecosystem which causes grasshoppers to explode because they have fewer predators and more food that only they can eat. This causes a problem for local farmers and your garden. Those grasshoppers will eat just about everything in their paths.
The displacement of native plants with alien plants is harmful to the vertebrate community as well. Many birds and mammals evolved with specific natives and can only use those plants to survive.
Another reason to avoid bringing in alien plants is that alien insects and diseases often come with them. These alien insects don’t have their natural predators here and their populations explode causing many problems for native wildlife, native plants, farmers, and your own garden.
As human populations continue to grow there are fewer wild places in the US. This means less habitat for our wildlife species. If we can learn to share our space with wildlife we can do a lot to help keep these animals alive. If we each strive to plant our yards with native plants we can create more habitat available to local insects which will attract local birds and mammals. A garden that is full of life is way more interesting and healthy than a sterile garden. The plants in your garden will benefit from having a full range of native insects living there. Insects can provide many benefits to plants including increased fertilizing potential. Soil enrichment, soil aeration, and pollination.
If for some reason you do have an insect over load on a specific plant that is causing harm to the plant you can use an organic insecticide soap. I would recommend only using it on the plant that is in trouble. This insecticide will kill the insects causing the problem and will biodegrade in 7 days. This means that 7 days later insects feeding on that plant will not die. I would recommend covering the treated plant until the pesticide has degraded. I would also rinse the plants down afterward. Then it will be free to use by other insects like butterflies without causing harm to them.
While it may seem against your nature to plant things that insects will eat, just remember that with time your insect ecosystem will evolve with many cool insect predators that will keep the more destructive species in check without having to spray harmful chemicals all over your yard. In the end by planting native species you will help your local wildlife and help sustain biodiversity in your area.
By Samantha Sader with Canyon's Edge Plants
Tally, D. W. 2009. Bringing Nature Home. Timber Press.