Companion Planting:

The Real Story

Janet Young, PhD

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College of

Agriculture and Natural Resources

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Thank you!

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Companion Planting Outline

Definition

Disclaimer

Brief History

Biological Benefits

Practical Considerations

The Last Word

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Companion Planting Definition

Growing plants near or next to each other to

provide a particular benefit to one or both

plants.

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Companion Planting - Disclaimer

There is very little scientific evidence for

certain types of companion planting. This

talk does not propose to ensure success with

any of the methods presented!

WHOA!

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Brief History – Ancient Rome

Varro, a Roman agronomist - 37BC

Roman Farm Management - Cato

“Full grown walnut trees render sterile

all the surrounding land.”

Pliny the Elder – 23 to 79AD

Naturalis Historia

“The (highly toxic) plant rue is a ‘very

friendly’ companion to figs.”

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Brief History – China

Growing Mosquito Fern in Rice Fields >1000 YR

Hosts a cyanobacterium that fixes nitrogen from air

Blocks light from getting to competing plants

Mosquito fern Rice

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Brief History – North America

Native American “Three Sisters” Garden

Variant of method used throughout North America

Mounds 12” x 20”, maize first, then squash, beans

Maize=pole ; Beans=N2 ; Squash=mulch/protection

Maize Beans Squash CA

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Biological Benefits

Nitrogen fixation – cover crops

Physical assistance – shade, mulch, support

Pest trapping – attract pest with other plants

Host finding disruption – using plant decoys

Attract beneficials - predators, pollinators

Repel pests – WHOA!

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Biological Benefits

Nitrogen Fixation

Plants e.g., clover, collect nitrogen from the air

Special bacteria assist the plant in converting

this nitrogen to usable nitrogen in root nodules

When the plant decomposes, the nitrogen in the

roots becomes available to neighboring plants

Three Sisters – beans provide this benefit

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Biological Benefits

Physical Assistance

Three Sisters: maize, beans,

squash

Mosquito fern and rice –

prevents weeds

Salad greens as a cover crop

– retain moisture, prevent

soil erosion

http://www.birdclan.org/threesisters.htm

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Biological Benefits - Pest Trapping

Pelargonium geraniums grown with roses draw away Japanese beetles; geraniums are toxic to the Japanese beetles.

Alfalfa grown with cotton draws away lygus bugs.

Japanese beetle

Lygus bug

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Biological Benefits - Pest Trapping

Rye is used to protect soybeans

from corn seeding maggots.

Sesbania is used to protect

soybeans from stink bugs.

Corn seeding maggot

Stink bug

B

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Biological Benefits Host Finding Disruption

How Predatory Insects Find Host Plants Host Plant required by predatory insect for feeding,

reproduction

Attracted by plant odor, and color green, avoid brown

Fly to several leaves of plant to assess suitability if host plant found

Chance of success increased if only a host plant is

available

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Biological Benefits Host Finding Disruption

CONCLUSION: adding non-host green plants

among host plants decreases host finding

success, and insect moves to a different area

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Biological Benefits Host Finding Disruption

Cabbage without clover Cabbage with clover

Biologist (2003) 50 (3), p. 132

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Biological Benefits Host Finding Disruption

How Predatory Insects Find Host Plants

From: Fig. 4,

Biologist (2003)

50 (3), p. 132

Cabbage root fly

searching for host.

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Biological Benefits Attract Beneficial Insects

Flowers and herbs are known to attract pollinators and predators of crop-destroying insects

Examples are chrysanthemums, sunflowers, coneflowers, alyssum, and flowers and herbs of carrot family

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Biological Benefits

Repel Pests - WHOA!

Chrysanthemum – (may) repel aphids, bed

bugs (Cimex lectularius), leafhoppers, spider

mites, harlequin bugs, ticks, pickleworms and

imported cabbage worms

Nasturtium – (may) help to control squash

bugs, cucumber beetles, and whiteflies.

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Biological Benefits

Repel Pests - Scientific Evidence?

Pests of the Garden and Small Farm, Mary Louise Flint,

PhD, UC Davis Department of Entomology

“While the concept of companion planting is appealing, research in this area has consistently shown that companion plants offer no pest control benefits under controlled conditions. While many plants have chemical components themselves that repel pests, this effect is localized and benefits are not extended to neighboring plants of different species.”

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Biological Benefits

Repel Pests - Scientific Evidence?

“The Myth of Companion Planting”, Linda Chalker-

Scott, PhD, Extension Horticulturist, Washington State University

“There is no scientific basis, however, for any of the several lists that exist describing ‘traditional companion plants’. Like horoscopes, these lists may be fun to use, but they should not be perceived or promoted as scientifically valid any more than astrology.”

I

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Biological Benefits

Repel Pests - True?

Tomatoes love marigolds

What does this mean?

Should one plant marigolds in between

(intercrop) tomato plants?

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Biological Benefits – Repel Pests – True? The Problem

Nematodes are unsegmented roundworms, usually microscopic in size

Plant-parasitic nematodes can kill crops

Galls from root-knot nematodes - University of MD Extension FS 825

Plant-parasitic nematodes are found in soil and are very difficult to control

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Biological Benefits – Repel Pests – True? The Experiment

Cowpeas seeded in a field with nematodes

Marigolds then planted next to the cowpeas in one part of the field

Nematode numbers, cowpea height, number of leaves, seeds/pod measured

– African Crop Science Conf Proc,.v. 8:1075, 2007

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Biological Benefits – Repel Pests- True!

The Results

Marigolds DID control nematodes in soil

Cowpea yield was doubled if plants were intercropped with marigolds in fields with nematodes

– African Crop Science Conf Proc,.v. 8:1075, 2003

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Biological Benefits – Repel Pests- YES The Conclusions

Authors stated that a bio-nematicide may be

released into the soil through the roots of the

marigold plants – African Crop Science Conf Proc,.v. 8:1075, 2003

More recent studies show that marigold roots release

the chemical alpha-terthienyl -- University of Florida Extension

In the Florida study only a cover crop of marigold

proved protective

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Biological Benefits – Repel Pests- True!

The Conclusions (cont’d)

Therefore, marigolds may be beneficial to

tomatoes (IF they are grown in soil with plant-

parasitic nematodes)

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Practical Considerations Use what we know works!

Nitrogen fixation – cover crops

Physical assistance – shade, mulch, support

Pest trapping plants

Host finding disruption

Plants that attract pollinators and beneficial predatory insects (know thy friends and avoid killing them!)

Some plants known to repel pests from neighboring plants

CO

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Gardening Plans - Three Sisters

From: http://www.reneesgarden.com/articles/3sisters.html

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Gardening Plans - Three Sisters

From: http://www.reneesgarden.com/articles/3sisters.html

L

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Three Sisters Garden

From: http://www.imrisk.com/threesisters/threesisters.htm

Corn is planted

the last day of

April.

Beans and squash

are planted mid-

May.

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Three Sisters Garden

From: http://www.imrisk.com/threesisters/threesisters.htm

Plants are growing well the first week of June.

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Three Sisters Garden

From: http://www.imrisk.com/threesisters/threesisters.htm

Plants are well established

by the end of June.

Zucchini squash

Butternut squash

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Three Sisters Garden

From: http://theexchange.thegrowers-exchange.com/herb-gardening-resolutions-part-2-companion-planting/

A More Mature Three Sisters Garden

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Companion Planting - Final Words

Don’t believe

everything you

read

And most

important of

all, have fun!

Try using what we know works

Experiment in your own garden

Be open to trying folk lore remedies

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Companion Planting – Selected Research References

Companion Planting: Basic Concepts and Resources by ATTRA, funded by USDA, https://attra.ncat.org/attra-pub/summaries/summary.php?pub=72

Companion Planting: Ecogardening Fact Sheet #10, Cornell U., 1994: http://www.gardening.cornell.edu/factsheets/ecogardening/complant.html

Companion Planting: http://en.wikipedia.org/wiki/Companion_planting

Insects Can See Clearly Now the Weeds Have Gone - by Stan Finch and Rosemary Collier, Horticulture Research International, Wellesbourne, UK http://www2.warwick.ac.uk/fac/sci/lifesci/wcc/research/pests/companionplanting/biologist_jun03.pdf

Marigold (Targetes erecta L.) as interplant with Cowpea for the control of nematode pests, by T.I. Olabiyi and E.E.A. Oyedunmade, African Crop Science Conference Proc. V. 8, p. 1075-78, 2003: http://www.acss.ws/Upload/XML/Research/389.pdf

The Myth of Companion Planting http://www.puyallup.wsu.edu/~linda%20chalker-scott/horticultural%20myths_files/Myths/Companion%20plants.pdf

Three Sisters (agriculture): http://en.wikipedia.org/wiki/Three_Sisters_%28agriculture%29

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Companion Planting – Popular Books

Cunningham, Sally Jean. Great Gardening Companions. Rodale Press, Inc., 1998.

Mayer, Dale. The Complete Guide to Companion Planting. Atlantic Publishing GroupInc., 2011.

Riotte, Louise. Carrots Love Tomatoes. Storey Publishing, LLC., 1998.

Riotte, Louise. Roses Love Garlic. Storey Publishing, LLC., 1998.

Roberts, Margaret. Companion Planting. Briza Publications, 2011.

Note: There is very little scientific evidence for certain types of companion planting discussed in these very popular books. Listing here is for informational purposes, and in no way ensures success with any of the methods presented!

WHOA! M

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University of Maryland Extension