Randy Sullivan remembers gardening as a teenager with his grandmother, who always planted her radishes with her cucumbers.
“My grandmother and I had a nice organic garden at one point. We grew tomatoes, potatoes, carrots, green beans, cucumbers, radish and corn,” Sullivan said. She always planted the radishes with her cucumbers. Unfortunately I never found out the reason before she passed away.”
Turns out, the late Lorraine Sullivan was practicing the generations-old technique of “companion gardening,” in which certain plants — when grown together — improve each other’s health and yields.
Radishes, for example, help repel the cucumber beetle — one of the banes of any gardener.
“People have been [companion gardening] for as long as there has been gardening,” Kate Garland, horticulturist with the University of Maine Cooperative Extension, said. “I think we naturally do companion gardening and don’t even think about it. Any time you have diversity in your garden, you have companion planting.”
Companion gardening, Garland said, can be an organic alternative to pest management, weed suppression and adding nutrients to the soil.
“When it comes to pest management in companion garden crops, one species will almost always be the ‘sacrificial’ crop,” Garland said. “It will be more attractive to the pests than the plant or crop you want to succeed.”
That sacrificial plant will attract the pests away from the desired plant, she said.
“Then you can go out and manage or destroy those pests in whatever manner you choose,” Garland said.
Eggplant is example of one crop that will attract an array of pesky bugs that want to nibble on peppers, tomatoes or cucumbers.
“Certain other pairings result in actually deterring insect pests,” Garland said. “A lot of people feel marigolds are good for that. Plants like garlic or chives have enough of a chemical compound that deter some insects and even mammals that can go after crops.”
When gardeners are not battling pests, they are pulling up weeds, but Garland said there are plants that can help that fight.
“Buckwheat, when used as a cover crop, is one that suppresses weeds,” she said. “After it is tilled in, you can transplant seedlings into the soil [because] the buckwheat will not allow seeds to germinate, but it does allow transplants to survive.”
Perhaps the most famous example of companion gardening is the triumvirate of squash, corns and beans, often planted together by indigenous peoples going back hundreds of years.
“Scientifically, we know that beans are a nitrogen-fixing legume,” Garland said. “Corn and squash are heavy nitrogen feeders.”
Nitrogen “fixing” plants produce nitrogen compounds in their root systems and when that plant dies, the nitrogen is released and available to other plants, which can’t produce their own nitrogen, to use.
“Some crops with really deep root systems can help ‘mine’ nutrients from deep down in the soil,” Garland said. “They help translocate those nutrients to the surface for other plants to use.”
The tillage radish, also known as a daikon radish, she said, is one of those deep-rooted crops that also has the added benefit of breaking up compacted soil.
“The tillage radish has an aggressive root that can break through hard soil,” Garland said. “They can loosen the compact soil on behalf of plants with whimpier roots.”
Above ground, flowering plants attract pollinators which greatly benefit an entire garden.
“I think we all naturally do companion gardening and don’t even think about it,” Garland said. “Any time you have diversity like ornamental plants with edible plants, you are automatically companion gardening.”
If space is at a premium, shade tolerant or root crops can be planted in between taller plants or, early producers can be paired with late bloomers.
Of course, just as there are extended family members who enjoy hanging out with some relatives more than others, there are those plant species which need to be kept separate.
Asparagus, for example, does well when planted with tomatoes, dill, parsley and basil, which seem to help repel slugs and attract friendly lady bugs; they do not do well when paired with onions, garlic or potatoes, which, in turn, are happy when planted with peas or thyme but hampered by pumpkins and sunflowers.
To keep a companion garden plan from becoming as overwhelming as the seating plan for a feuding family wedding, Garland recomments consulting companion species charts published by seed manufacturers or available online.
“When it comes to your expectations of companion gardening, look at as much of the research-based information as possible,” she said. “If you think one type of plant is going to work and solve all of your problems, that is just not going to be the case.”
Back on his homestead, Sullivan can’t wait to begin his garden, using some of the old family pairings.
“My grandmother and I both enjoyed being in the garden,” he said. “She will definately be in my thoughts as I add my own garden to the homestead.”
Of course, not all of Sullivan’s youthful companion gardening attempts were wholey encouraged by Lorraine Sullivan.
“When I was a teenager, I put marijuana in the corn,” he recalled with a laugh. “She never made me cut it down, but she did say to keep [the marijuana] in the woods after that.”
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