Beginning Gardeners Series: June

  • Difficulty Rating: Beginner


companion planting

If you're a beginning gardener, as you research ways to improve your gardening skills, companion planting is a term that might frequently pop up and begin to become more familiar to you.

If you're not certain what it is, companion planting is the deliberate placement of certain plants near one another with the belief that at least one of the plants will benefit from a characteristic of the other. Although there are many suggested benefits associated with companion planting, pest control, soil enhancement, and protective shelter are some of the most common benefits gardeners focus on when formulating a garden plan.

The use of companion planting for pest control benefits occurs in four different ways:

1.  Some plants are used to disguise the presence of another kind of plant in an effort to protect it from damage by pests. An example of plants used in this way is the placement of rosemary, sage, lavender, and/or oregano plants near those which are host plants for aphids. The strong scents of these plants is believed to mask the scent of the host plant making it difficult for the aphids to locate it.

2.  Plants are sometimes used as companions for pest control through a method called trap cropping. A plant is placed near a different kind of plant because it has qualities that cause it to be preferential to a pest from which they are both susceptible to damage. In essence, it is sacrificed for the benefit of it's companion. Planting certain varieties of squash plants near melon plants is one example of this.

3.  Placing plants that produce substances that are toxic to a pest near other plants that are at risk of infestation by that same pest is another method of companion planting. For this reason, certain kinds of marigolds are believed to be effective in the fight against certain kinds of nematodes (microscopic thread-like worms that can attack the roots of  plants), and are often suggested as a companion plant for tomatoes.

4.  Plants that attract insects (as well as birds, frogs, and lizards) that are predatory or parasitic to those that cause damage are often used as companion plants. An added benefit to this method of companion planting is that many of the plants used for this purpose also add beauty to a garden. The use of Sweet Alyssum to attract hoverflies, whose larvae is a predator of aphids, will add fabulous fragrance to a garden. And, there is a wide variety of brightly blooming flowers that, in addition to being stunning to look at, can be used as companion plants for the purpose of drawing in beneficials.

Companion planting is also believed to, in some cases, enhance soil qualities. Beans, other legumes, and lupines (which are also considered a companion plant for attracting beneficial insects) are nitrogen fixers. Nitrogen fixers are plants that take nitrogen from the air and deposit what is not used for their own growth back into the soil when they die back and their roots decompose. This is actually crop rotation (because the plants that benefit from nitrogen fixing are planted after the nitrogen fixing plant is gone and decomposed), but you will often see it included in articles written about companion planting. And it is a good practice to use!

When plants of varying height are grown together, they can provide one another with protective shelter. Plants that grow low to the ground can act as a mulch to taller plants, helping to retain moisture in the soil. Taller plants can provide protection to shorter plants that have lower sunlight requirements. A good example of this is growing cucumbers on a trellis set at an 45 degree angle with lettuce growing underneath.

I would be remiss if I didn't share that the topic of companion planting doesn't always come up smelling like roses! There is controversy amongst gardeners as to the validity of some of the practices used and some of the claims made about companion planting. A suggested combination of plants for battling one kind of insect may be ignoring problems that can arise from another insect that is also attracted to the plant. For instance, marigolds may help decrease nematode populations (also highly debated), but marigolds can also attract large populations of spider mites. Another problem you might encounter is a combination of plants listed as compatible by one person can be listed as incompatible by another.

If you are a beginning gardener, I encourage you to do some research on companion planting and as you read the advice of others, keep a list of companion plantings that sound appealing to you. Then do some individual research on those plants. Look for problems growing them, such as pests and diseases they are susceptible to. Look for characteristics that are beneficial. Find out if the plants are invasive and might leave you replacing one problem with another. Search for even more information about characteristics that are suggested as benefits to determine if the advice could be based on tradition carried from generation to generation and has since been proven to be ineffective.

It's easy to become overwhelmed or frustrated with the conflicting information and decide you don't really need to be informed about companion planting. But the reality is that anyone who plants more than one kind of plant in close proximity to another is companion planting! Learning the good and the bad about the plants we choose to grow will better equip us to make choices that increase our enjoyment with gardening and decrease our frustration.