Slow Food USA Townhall Call: Preparing Your Three Sisters Garden

Reader Contribution by Pamela Sherman
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Welcome to the written recap of the Slow Food USA’s Garden Campaign, Plant a Seed: Food for Change, Townhall Call. It took place March 15, 2018 with presenters Stephen and Cindy Scott, co-owners of Terroir Seeds/Underwood Gardens in Tucson, AZ and Clark Harshbarger, Resource Soil Scientist, who advises on Soil Health with the Natural Resource Conservation Service and was produced by Anna Mule’, Slow Food USA Communications and Campaigns Director. I moderated and have added some commentary here.

Four Soil Health Principles

Clark Harshbarger started us off with an introduction to soil health and a list of four basic principles applicable to all soils. “Mother Nature by herself creates perfectly healthy soil, thanks to the perfect working relationship between plants and the community of soil organisms. We humans cannot improve on the soil ecological environments she has already perfected.” Masanobu Fukuoka’s book, The One Straw Revolution, tells us, as Harshbarger says: “the macro and micro-organisms are doing things in the soil that our mechanics, our steel, our technology cannot easily replicate– and if we can replicate them, it takes more work or energy from fuel or intensive labor. Science is necessary, but it doesn’t solve problems; human creativity, all of us working together, does.”

One of the most useful things we have started to do together is figure out how to give Mother Nature the best possible working conditions to renew the soil we have messed up. Here are four ways to do it:

Armor the Soil

Mulch it. Put your cover or target crop residue back on the soil to keep it covered. No bare soil.

Keep a living root in the soil at all times.

“The plant canopy helps protect the soil from rain, which typically falls at 25-35 mph. And from wind. It moderates temperature extremes at the soil surface. Maintaining a living root at all times keeps the sun energy flowing into our plants and soils. The soil microbes are active any time the soil goes above “biological zero,” 40 degrees F. They are fed by sugars exuded by the plant roots and in turn feed the plants its needed nutrients. The Three Sisters are all warm-season crops, so plant cool season crops (those in the cabbage family, for instance) in the early spring. In the fall plant cover crops which include legumes.”

Minimize Soil Disturbance

When we disturb the soil, even with strip or conservation tillage, we are damaging both the bodies and homes of the microbes which build our soil, and we damage the structure of the soil itself. “All the Three Sister families have extensive relationships with mycorrhizae in the soils [microbes which are key for soil health and carbon sequestration.] When we till our soils or try to work in green manures, we disturb the mycorrhizal filaments in the soil, creating a harsh envrionment for them.”

Harshbarger related a central experience in his life which illustrates this principle. “About ten years ago in Texas I met a dear friend, a brother, of the Apache Nation. His name is Ray Salazar and his role was to be caretaker of soil and seed in his tribe. Ray taught me how to plant the traditional way, with minimal soil disturbance. We would plant in groups of three. We would take a planting stick. One person would make the hole in the ground, a second would plant the seed, a third would follow and cover the hole with soil. In all, we made a disturbance in the soil no bigger than a quarter and sometimes as small as a dime. That’s really important. The Three Sisters are all above ground, so it’s easy to minimize soil disturbance with this community of plants.”

Plant Diversity

“Crop diversity is built into the Three Sisters system, although these are 3 warm season crops.” The more diverse the plant species, the more diverse the soil organisms they work with, the more fertile and healthier the soil is likely to be. Plant cool season crops before them and over-wintering cover crops after them [and, if you can, a hedgerow of pollinator plants around the garden, with perennials and natives in the mix.]

Incorporate livestock

“Try to use finished compost with manure amendments in it. If you have goats or sheep, let them graze the garden.” Let them graze the cover crops to kill them at the appropriate time and let them graze the residue after the target crop is harvested.

Five Crucial Soil Habitats

Harshbarger then described five crucial habitats within healthy soils; they are key to healthy soil function. They exist only when plants are able to work together with the community of soil organisms without disturbance. “These five types occur all over the planet in every soil type, every climate, yet in specific are unique to each location.” These habitat types are:

Detritus—the World of Decay

 “This is the decaying layer where mulch (crop residues, leaf litter) starts decaying into the soil. It keeps consistent temperatures consistent, preventing wild fluctuations. Spiders and some earthworms live in its upper part. It’s critical to keep that layer on your soils.” Disturb as little as possible.

Drilosphere—the Earthworm-Casting World

The drilosphere  is the part of the soil which has gone through the digestive tract of earthworms, or the lining of an earthworm burrow. It’s very rich in nutrients. Do not disturb.

Rhizosphere—the Root Zone World

“This is the soil around the root zone, where the mycorrhizal network lives. In fact, almost all the soil organisms live in concentrated population densities here. This is where the plant excretes its sugary carbon exudates –different polysaccharides, enzymes, different chemical signatures–to feed the soil microbes that will go get the nutrients the plant needs, but can’t access by itself. The microbes are not only able to mine these minerals from rocks and organic matter in the soil, they also convert them into plant-available forms. Many of these relationships are as old as time. Many of them have taken place since long before the human species was part of the ecosystem here on earth.” Keep a living root in the soil at all times and disturb these interactions as little as possible.

Porosphere—the World of Soil Pores

Earthworms tunnel, creating pores–air pockets and passageways–allowing roots to go deeper, allowing oxygen and water to infiltrate quickly into the soil, retaining the water in the soil deeper so it doesn’t run off, holding the water in the soil to feed the soil food web for a much longer time. When we disturb our soils, the first thing we destroy is these macro air and water spaces.

Aggregate Sphere—the Building-Block World

“Aggregates are the building blocks of soil, made of minerals, organic matter, air, water, and biology. The minerals and organic matter are bound together by glues secreted by fungi and other microbiology. Aggregates are critical. They make healthy soil resilient to hard rains, to extreme changes from air and water pressure inside the pores. It is absolutely critical we keep living plants in our soils to keep the aggregates freshly glued.” When we disturb soil, we rip up the aggregates.

Stephen Scott then introduced his and Cindy’s presention: “We also believe everything starts with the soil. Clark, loved you talking about not tilling and not disturbing those soil horizons and the biospheres there. At the gardeners level, we say get on Mother Nature’s Team, work with her instead of working against her, and you will be amazed at the results and success you have: the garden will be more productive, the health and productivity of the soil and the plants will be better and continue to increase, flavors will be better, weeds will decrease; it’s kind of amazing.”

Anna Mule’ told of sending 500 Three Sisters Garden kits to gardens all over the country. These kits all held seed for Stowell’s Evergreen Corn, Christmas Limas, and Long Island Cheese Squash—all heritage varieties on the U.S. Ark of Taste. Stephen and Cindy’s presentation focused on these three varieties. Stephen Scott began:

Stowell’s Evergreen Corn

“Stowell’s is old timey, one of the first sweet corns developed, came around the 1850’s and it’s white corn, better flavor than what you will find with any of your supersweet corns and not as sugary sweet. The flavor complexity–its profile will be much different.”

Why you need to plant in warm soil. “All these Three Sisters crops are warm-season. All need warm soil to be planted in. To test the soil you can do the old English gardener’s trick: drop your pants and sit on the soil. If it’s too cold to sit on, it’s too cold to plant in! Or you can get a digital thermometer and if it’s 75 degrees or better, you are good to go. The ideal soil temperature for all these varieties is 80 degrees.Now there are always season extenders: the French cloche, row covers, a lot of other techniques, but bottom line is you need a good warm soil, otherwise your germination will be significantly delayed. Five to ten degrees cooler may mean the corn does not come up for three weeks–that’s how significant a difference it can be.”

For Best Pollination Plant in a Block or With the Wind Flow

“Corn is a heavy feeder. Most corn planted in poor soil will give a disappointing result, both in production and in flavor. Deep, dark rich, aromatic, fertile soil is what corn needs. Ideally corn is planted in a block because the pollen is windblown. If you can’t plant in a block, you want to plant with the direction of the wind flow so the pollen blows from the leading plant back to the other plants. You can get better pollination this way. If you have to do rows, try to do them as thick as possible, do three or four lines of plants, not just one.”

Mutual Aid and Bed Designs

“Research has found the beans and corn in the Three Sisters grouping help each other and the squash helps everything else. Corn can help deter bean beetles. Depends on where you are how you are going to plant your Three Sisters garden. In the arid Southwest it would do better as a Zuni, Navajo, or Hopi Waffle Garden. You want to dig down to put the garden in the lowest place to collect rainwater. The plants need as much as they can get. Sink the beds, so they are the last place the water goes. The Mandans in South Dakota would plant the corn and beans together, but would use the squash as fencing, to delineate the family garden plot. There’s no one absolute right way.”

Origin of the Stowell’s Evergreen Name

Cindy added: “the Stowell’s Evergreen name came from it staying green for a long time after you actually picked it—it was fresh corn that lasted a long time.” Stephen added: “Early frost came in and a desperate farmer just yanked the plants whole and hung them upside down in the barn and found the corn continued to ripen, thus was “ever green.” 

Christmas Lima Beans

Mutual Aid

“They need warm soil. Beans help fix nitrogen from the air into the soil, which helps give a boost to corn and squash. Pole beans minimize corn worms.”

“Pole bean anchor corn to minimize lodging (falling over) from wind– our winds can get 20-40 mph. Heirloom corn like this has better roots to help stabilize it. It’s not planted as tightly as some of the hybrid corn because heirloom corn stalks don’t depend on each other to hold each other up.”

Pole or Bush Beans

“But if you are in an area with not as much wind, a bush bean can work just as well. You can do both. Bush beans help protect the soil, keep the moisture in, and keep it cooler, so bush beans moderate plant stress over the hot summer, so you get more consistent growth.”

Cindy explained: “it depends on the age group the school garden is serving—bush beans will be at the level of the younger kids, pole will be much taller for middle to high school students.”


“And Christmas Limas are wonderfully– nutty and flavorful. Folks who say they don’t like limas cuz they don’t like the flavorless ones sold in the store are always amazed at the flavor of the heirlooms and homegrown food. Christmas Limas are pretty and big.” 

Long Island Cheese Pumpkin

“It’s a moderately heavy feeder—grows best in rich, fertile soil for the richest flavor and production.

Depending on your space constraints, this pumpkin gets up to 20 pounds, so if you want smaller scale, you may want to look at New England Sugar Pie.”

Vine Design

“Two pumpkin vines can take up as much space as a couple hundred corn stalks. You can train those vines to grow where you want them. If you are doing the Southwest style, the squash will be in the sunken bed with the others. If more the Mandan style, the squash will be outside the corn and beans. Depends on what you need. If it’s a raised bed or square foot gardening type of situation, we always encourage planting on the corners because they can sprawl into the walkways.”

“You will have sprawling growth you will need to corral; you can direct them back where you need them. You can train those vines to grow where you want them. Large leaves shade soil, keeping it cooler and retaining moisture for other plants underneath. One of neat things with pumpkins or squash is you can grow some heat-intolerant herbs like cilantro underneath the leaves, in their shade. Redirect the vines so the leaves cover the cilantro. One gardener we knew had cilantro that did not bolt for two months despite 100 degree days because of this. Show the kids: see how moist and cool it is under the leaves compared to two feet away, where the soil is hot and hard as a rock and nothing grows there.”


“We consider Sunflower as the eldest sister; we know from research it’s the oldest domesticated food in North America. Research has shown how sunflowers have traveled with hunter-gatherers and as people started taking up farming more. Sunflowers work well with the Three Sisters as a windbreak, shade, cover crop; they have heavy roots that dig down and break up compaction and help improve soil over time. But plant them three feet away from the other sisters, as they are allelopathic.”

Building Great Soil

“The one thing we have worked with customers all across the country on is improving the soil.

We agree with Clark: manure-based compost is excellent—apply in spring and fall. This may be harder to find in cities. Learn to stack nutrition—coffee grounds, charcoal, minerals, milk and molasses. We have more information on composting here . Do cover crops in the fall and spring. We have more information on cover cropping here and on our Facebook page. Plant pollinator attracting flower mixes for better production and to improve production and amazement in the garden, especially with kids, whether in preschool or high school. The more pollinators the better; you’ll have bigger and better produce that season and in the long run.”


What do you do if you are starting a new bed and there is grass there? Can you remove the sod and add a layer of compost and manure?

Clark Harshbarger: “Ranked in order of managing for soil health: the way I prefer is passive solarization with black, breathable landscape fabric: spread it over the sod six weeks before you want to plant there. There will be 70-80% kill. Two, you can scalp sod and try to get the crown [grub hoe]. Three, in the worst case you would till it, then lay down 3” of compost, 3” of straw, and then plant into it.”

Stephen Scott: “If you need to till, plan a season ahead and go in with a cover crop mix—rye, vetch, or others. You won’t get to planting your target crop that first season because the soil will need a season to chase away the roots and improve the soil with the cover crops.” 

What are the best methods to test soil health? Pam: “Professor Miguel Altieri and colleague’s soil health indicator test uses observation alone. It was developed for vineyards, but can be used with soils of other crops; you can tweak it as needed. It can be fun for students because you can graph it into an amoeba.”

Clark Harshbarger: “We teach kids to use their five senses—taste, smell, touch, describe the colors, close their eyes and feel the soil. Children can quickly tell you healthy from unhealthy soil. You can also tell by the amount of critters present. You can do Albrecht and Reams tests for mineral profiles.All soil has the ability to change its health. You can upgrade and degrade it. Sometimes during the year it goes through both of those processes. It can always do better. Compare your own soil to itself over time.”

When does nitrogen get into the soil from the beans to help other crops such as the corn? Some agronomists say only when the dry bean itself is returned to the soil, some say any part of the dead bean plant returned as mulch can do this, some say the bean plant when alive will share nitrogen with its companions. What’s accurate?

Stephen Scott:” It depends on the type of bean, how strongly they fix nitrogen, the type of soil, whether there are the right bacteria to fix nitrogen present. So you need to plant into good, rich, fertile, healthy soil. Beans must not be the only provider of nitrogen; they can only provide some, but not the majority. Most will come from animal manure-based compost and cover crops.”

Clark Harshbarger: “The legume will take care of itself first. And free-living, nitrogen-fixing bacteria are in the soil by the millions, we just can’t quantify them in laboratories. We haven’t yet been able to put genus and species on them. They swap DNA based on temperature and environment; there’s a lot more going on in the soils than we know about. Use amendments if needed. All plant tissue has nitrogen in it, air has nitrogen, nitrogen is not a limitation if you have a good food web!”

What are good crops to plant before the Three Sisters, before soil warms up? Stephen Scott: “The cole/kale/cabbage/broccoli family, spinach, lettuce, anything that does well in a cooler soil (50-55 degrees). You can use hoop houses, high tunnels, row covers for warmer soil. Keep active, living roots in the soil at all times.”

Does corn transplant effectively from greenhouse to field? Cindy Scott: “In a shorter, cooler season: yes.” Stephen Scott: “the roots are very delicate, sensitive to changes. Transplant shock will make them bounce back a month later. Start them not in tiny seed containers but in larger soil containers, 6” or 8,” and be super careful when you transplant. If you plant in tiny containers the plant will read its environment and think “I’ve only got 3” to work with here and it will stay small.” Pam: “We have had good luck with this. My husband transplants when the seedlings are 3” high, into very wet soil.”

Should squash be transplanted from the greenhouse? Stephen Scott: “If indoors, start it in a larger pot.”

Can you give us a diagram of the best Three Sisters planting configurations? Pam: “If you want to see some articles on this, there’s one from Native Seeds Search with a downloadable handout, and others from Cornell University Extension.”

Cindy Scott: “It depends on your environment. Talk to other gardeners in your area. Depends on the wind, etc. Each situation, environment is different.” Stephen Scott: “Don’t be afraid of breaking established rules.” Clark Harshbarger: “Human creativity!”

Are sunflowers allelopathic to beans?Stephen Scott: “Sunflowers are one of our most allelopathic plants, next to rye—good for weed suppression. We have to ask: how long does the allelopathic effect last? Sunflowers are good as a wind break– three feet away is fine. Don’t plant beans right next to sunflowers. And the allelopathic effect is much less on a foot-tall seedling as compared to a newly-germinated seed.”

Define allelopathic effect? Stephen Scott: “there is a phytochemical some roots exude which decreases the ability of other seeds in the soil nearby to germinate. So weed seeds can’t germinate either for 4-6 weeks. Mow cover crops when they are a foot tall. Plant in there.”

Do we need to do crop rotation with a Three Sisters garden?

Clark Harshbarger: “There are cultures that are givers and those that are takers, according to the principles of Iroquoian and other indigenous cultures. We have been a “taking” culture. Indigenous cultures that have lasted are “giving” cultures. We want to give more than we take from our resources base. So you can plant for two to three years in same spot, but then rotate for the next two to three years. You can rotate in a circle or in rows or whatever. We want to try to give back more than—or at least as much as–we take. We can do by using cover crops or other such plants we are not actually mining from.”

Stephen Scott: “Clark, I like your use of the word mining, especially when you talk about heavy feeders. Sometimes in as few as three years if you don’t replace what you’ve taken from the soil, it can go downhill. So you do need to rotate. Do a cover crop, compost, manure. Feed the soil. Keep it healthy.”

The photos of Cindy and Stephen are from Terroir Seeds/Underwood Gardens. The photo of  Clark Harshbarger is from here.

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