Companion Planting in the Vegetable Garden

Plants, like people, influence each other and some get along better together than others. The same kind of thing happens with plants in the garden with companion planting. Companion planting is when two or more crops are planted near each other with the theory that they help each other in nutrient uptake, better pest management, better pollination and higher yields. Companion planting is about bringing pollinators and beneficial insects to your garden to promote biodiversity. For instance, plant flowering herbs such as dill, parsley or fennel near melons and squash to lure pollinators. No pollination = no vegetables or fruit.

You can enlist the help of beneficial organisms such as lacewings, mantids, spiders and predatory mites in the battle against pest populations by growing plants that create a habitat for those bugs in close proximity to the vegetables that are under seige. Plants such as basil, dill, parsley, fennel and cilantro are a few that provide shelter and food for various life stages of predatory and parasitic beneficial bugs.  In addition to attracting the natural enemies of garden pests, plants like buckwheat and clover are excellent choices for attracting bees to adjacent pollinator-requiring crops (and I might add that they make a very good weed-suppressing cover crop).

Make the most of a small garden plot by companion planting corn, pole beans and winter squash (often called “the three sisters” by Native Americans). This technique is often referred to as “intercropping” or “interplanting”. Because of each species’ growth habits, the three grow well in the same space (though competition for nutrients still exists). Cornstalks, with their tall, thin growing habit provide a living trellis for the beans to climb up, while the vining, low-growing, large-leaved squash plants shade the ground to help the soil stay moist and suppress weeds. The beans will contribute nitrogen to the soil for the next growing season if the plants are worked into the soil after they die.

Something to keep in consideration when choosing companion plants is their root system: think about where in the soil the plants roots grow. Place deep rooting plants near the more shallow rooted ones so that their respective root systems will be in different soil states and not competing with each other for nutrients and moisture. 

To combine getting the most from a small garden space and companion planting, consider how fast each plant grows. Plant fast growing plants, such as lettuce, radish and spinach, with slower growing plants, such as tomatoes and peppers, so when the first crop is harvested, there is room for the slower growing plants to mature.

A very well known example that many of you may already know about when it comes to companion planting is that of marigolds grown in and around vegetable crops as a pest repellent. Research has shown that the roots of African and French marigolds do produce biochemicals that are toxic to root nematodes which are very small worm-like organisms that can kill plants or reduce yields (cals.arizona.edu , Marigold and Nematode Management, June 2004).

The number of scientific studies regarding companion planting is small compared to the number of books, lists and charts about companion planting based on anecdotal evidence. Please note that choosing a companion planting scheme not grounded in science may result in a bit of disappointment. You might like to go to the website of ATTRA Sustainable Agriculture to view their publication titled Companion Planting & Botanical Pesticides: Concepts & Resources at www.attra.ncat.org. However, personal observations of effective planting combinations and being able to replicate those combinations and observations over a number of years of gardening will confirm what does and does not work for you. Keep records of your successes and failures for future reference.

As always, Happy Gardening! 

More information about gardening and related subjects is available online at www.hort.purdue.edu/ext/garden_pubs  The Purdue University Cooperative Extension Service can be reached at 499-6334 in LaGrange Co., 636-2111 in Noble Co., 025-2562 in DeKalb Co. and 668-1000 in Steuben Co.

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