PITTSFIELD, Maine — In Iroquois legend, three sisters — namely corn, beans and squash — are inseparable, growing and thriving together. But more than a legend, this hints at something important for growing: Science shows that planting certain crops together can yield more bountiful results and potentially keep pests at bay.

Known as “companion planting,” it’s something farmers, horticulturists and perhaps even your grandmother all do with varying degrees of success. According to Kate Garland, a horticulturalist at the University of Maine Cooperative Extension, some plants just do better when planted next to each other.

“A lot of people feel very strongly about companion planting. Maybe they learned about it from their grandfather or grandmother, so it may not be based in science — but it works,” Garland said. “But, no one person is going to be 100 percent right all the time.”

Planting folklore

With the three sisters, each plant plays a key role. The corn provides a natural pole for the bean vines to climb. The beans improve the fertility of the soil by providing plant-soluble nitrogen while also stabilizing the spindly stalk. Meanwhile, the squash vines become a sort of ground cover, preventing weeds and retaining moisture in the soil.

“There is some validity to the folklore, and there’s a lot of beauty in that sort of tradition,” Garland said.

And that’s a beautiful tradition that’s honored every day at Snakeroot Organic Farm in Pittsfield.

Farmer Tom Roberts wagers the number of fruit and vegetable varieties growing at his small farm every year is around 150. But he can’t know for sure. What he does know is that farming, at least for him, is all about biology.

The 68-year-old, who sports a full, bushy white beard, weathered hands and dirt under his fingernails, has been farming for more than 30 years. He knows what plants thrive together and which ones when sowed next to each other run the risk of producing what his partner of 20 years, Lois Labbe, calls “zumpkins” (pumpkins and zucchini.)

But aside from the Iroquois legend, both Roberts and Garland said there are many more pairings, some having to do with plant compatibility, others with timing. With some minor tweaking, most of Roberts’ farm-tested techniques can easily be implemented in home gardens throughout Maine.

Dealing with pesky pests

Bug infestations can be the end of an otherwise thriving garden — that’s why hundreds of gardening blogs, articles and books devoted to natural methods explore pesticide-free ways to get a handle on the little buggers.

LoLo Houbein, in her book “One Magic Square,” recommends planting marigolds in the center of a garden plot or throughout rows.

Scientifically, Garland said marigolds deter nematodes (a type of worm-like roundworms), but she hesitates to say they are the complete solution to spray-free pest management.

It’s a fact Labbe knows all too well.

“I had the most beautiful fields full of marigolds … but the bugs were still there,” she said with a chuckle, remembering one summer when she put the marigold-pesticide theory to test.

Instead of just marigolds for the sake of pest control, Garland suggests people consider planting a variety of flowers so they act as pollinators.

But if you’re dead set on doing something to deter bugs, Roberts suggests planting peppers and basil together. He and Labbe plant one pepper every 18 inches and fill in basil between them a few weeks later. The pungent smell of basil masks the smell of the peppers and helps keep bugs at bay.

Rotating crops also can help prevent bugs that tend to burrow down in the winter and will wake up to the very food that drew them in the first place.

“You’re gaining a week or two because the bugs haven’t been fed right at their doorstep,” Roberts said.

Timing and space

Roberts doesn’t use any pesticides or chemical fertilizers at his farm. Because of that, timing is crucial. Seedlings start growing in a sort of greenhouse room attached to his home. Once it’s warm enough, they’re transferred to one of six detached greenhouses. From there, they are planted in the 5-acre field out back, a few varieties at a time.

Garland suggests people consider staggering their planting similar to Roberts’ and Labbe’s approach. For example, broccoli plants generally grow quite large, but they take a long time to mature. By the time the leaves are big enough to shade other plants out, a gardener could have already harvested an early crop such as radishes planted nearby.

Roberts also recommends planting tomatoes with peas. Tomatoes, a late maturing crop, will often grow too big to be closely planted to other vegetables. But peas will reach maturity long before the tomatoes grow too large and also replenish the nitrogen in the soil.

Not a fan of peas? Consider planting lettuce under or near tomatoes. Lettuce, also an early crop, gets bitter in the heat but will thrive under the shade of tomato leaves.

These days, Garland said, technology makes tracking a garden’s success or failure easy. She suggests people use their smartphones to take photos of their garden and consider changing up the plant location each year.

“It’s not much to do with the plants liking one another but more about how the plants grow,” Roberts said.

Avoiding ‘zumpkins’

For as much help some plants can give others, sharing a space can be detrimental.

Garland often recommends home gardeners maximize space by using vertical trellises, but she warns people to be mindful of the sun.

“You have to keep those sorts of things on the north side of the garden so they don’t shadow out the other plants,” she said. Unless of course you’re talking about leafy greens that thrive under shade in the heat of summer.

However, for home gardeners interested in saving seeds, companion planting brings with it a certain risk. Some plants cross-pollinate and create wacky hybrid offsprings the next year such as the “zumpkins” known to appear in the Roberts-Labbe compost pile.

“Peppers and squashes cross like crazy, and sometimes things cross into totally different things,” Roberts said.

He recommends planting things such as sunflowers and large plants on the north side of the garden so they soak up the most amount of sun without putting the other plants at risk of shade.

And if all else fails, next spring, try again.

“Make a map in the spring, try it and then correct it in the fall as you need to,” he said.

Natalie Feulner is a journalist and “semi-crunchy” cloth diapering momma to a rambunctious toddler named after a county in California. She drinks too much tea and loves to climb rocks but not at the...