Companion
Planting
• By
Pam Larson Frink
• Is
there any truth to this words of wisdom?
• Plant
dill next to tomatoes to prevent hornworms
• Carrots
love basil
• Basil
likes tomatoes
Or are these claims just folklore?
“I used to wonder about that myself. Thought it was just a
bunch of mumbo-jumbo.”
- Hans
Solo from Star Wars: The Force Awakens
• Around
for thousands of years.
1st documented instance: ‘three sisters’ planting.
corn provides support
beans add nitrogen to the
soil
squash leaves provide mulch
Most literature is just ‘mumbo-jumbo’
Little scientific proof until recently
Only sharing scientifically proven methods
• Caution
There are over 18 million web pages that have the words
‘companion planting’ in them. Over 3,000 books on Amazon.
Search by ‘intercropping’ or ‘polyculture’ to get better
results
If they don’t explain WHY a particular plant pairing
works then do some research:
Maybe
their recommendations work and it hasn’t been
scientifically
proven yet or
Maybe
they don’t work and it’s a waste of your time
Start
your own research – keep good notes
• Gardens
as Ecosystems
• Our
ornamental gardens have evolved to include plants for:
• Vegetable
Gardens Are Ecosystems Too
Vegetable gardens are more than just a square of land
producing food for humans.
Diversity is the key to a thriving vegetable garden that
provides:
• What
is Companion Planting?
• Improve
the Soil
• Provide
Support and Shelter
• Weed Management
• Reduce
pests
• Increase
Pollination
• About
the Facts
Note: all examples have been from studies on nonprofit agricultural research institutes,
universities, working farms and various corporate and private research
programs.
Obviously, these are not exactly like your home garden,
though many research facilities also set up small scale test gardens similar to
home gardens.
There are many variables in growing plants and gardens, so
your own research in what works and what doesn’t is the best proof.
• Soil
Improvement
Mycorrhizal fungi – reside in the soil and form
symbiotic (mutually beneficial) relationships with plants. The fungi bring
hard-to-reach nutrients and water directly to plant roots, and the plants
provide the fungi with carbohydrates.
Practice NO-TILL gardening
Plant Cover Crops
usually planted before or after regular crops to improve
soil structure
Choose carefully
Top Choice: oats – killed with freeze, provide organic
matter
Add Nitrogen
Bean and Peas fixate nitrogen from the air into their roots
Improve compacted soils
Some root vegetables break up heavy soil
• Improve
Nitrogen in Soil
Legumes such as peas and beans add nitrogen to the soil by
forming a mutual relationship with rhizobia, a root-inhabiting bacteria, that
take nitrogen from the air and convert it into a plant-available form. The
plant forms nodules on the roots which house the bacteria.
When the plant dies, the nitrogen then becomes available to
other plants in future plantings.
• Examples
of Companion Planting for Soil
Potatoes and Beans – alternate rows or intermix, adds
nitrogen
Fava beans and Corn – farmers needed 50% less nitrogen when
growing sweet corn
Peas and Lettuce – Shade from peas keeps lettuce cooler and
adds nitrogen
Cowpeas and Peppers – provides both nitrogen and reduces
weeds
Forage radish, Turnips – long tap root breaks up soil,
brings up nutrients
Comfrey has deep roots. When leaves are chopped and spread
on the garden, it can provide nutrients from deep under ground and make them
available in the topsoil.
• Support
and Shelter
Tall, sturdy plants provide support for vining crops
Taller plants shade shorter plants
Examples of Companion Planting for Support:
Corn and beans
Sunflowers and mini pumpkins – strong enough for small
squash crops
Sunchokes (Jerusalem Artichokes) and Cucamelons
Tithonia and Malabar Spinach
• Weed
Management
Companion planting either prevents weeds from growing by
covering the ground or by allelopathy.
Allelopathic (ə-ˌlē-lə-ˈpa-thik) - the suppression of growth of one plant
species by another due to the release of toxic substances.
e.g. Walnut trees which exude juglone that inhibits growth
of other plants
• Weed
Management Examples
Living Mulches – alternate between rows of crops
- grow underneath tall crops
- can be walking paths
Caution – don’t select a plant that competes with resources
or produces lots of seed
Crimson clover and cole crops – many studies found less
weeds and clover will die over the winter
White clover and blueberries/strawberries or fruit trees –
plant between rows, mow before harvest of berries, increase pollinators too
Oats and tall crops – do not direct seed as oats are
somewhat allelopathic
• Reduce
Pests
Several ways this works:
-
Luring pests away using trap crops
-
Disrupt feeding behavior
-
Reduce egg laying
-
Physical barrier
-
Improve diversity
-
Increase predatory insects
Only <1% insects are threat to agriculture crops
• How
Do Insects Find Their Food
Plant’s appearance
Volatile chemicals released by plant
Key is to disrupt one or both methods to confuse the pest
-
appearance is masked so pest can’t recognize the host plant
-
volatile chemicals released by plant companion to mask host plant
Masking VS Repelling
Originally it was thought some plants such as marigolds,
sage and mints repelled pests by their strong fragrance
But after many studies it was found their odor masked the
volatile chemicals from the host plant.
• Trap
Cropping
Planting something that becomes sacrificial to protect host
plant
Position of trap crop depends on insect trapping, must
experiment
Plant trap crop several weeks before main crop (this may be
difficult in Minnesota’s short growing season)
• Examples
of Trap Cropping
Cabbage and Collards – collards lure diamondback/cabbage
moths
Squash and Blue Hubbard Squash – Blue hubbard squash lures
squash bugs. Plant hubbard squash 3-4 weeks before regular crop of squash.
Locate on edge of garden.
Most squash need 100 days from direct seeding.
• Examples
of Disrupting Feeding
Many pests identify their food sources through scent or the
physical outline or shape of the plant. By planting companion plants as ground
covers or inter-planting amongst the host plant it is harder for the pest to
find the host plant.
Pests can be confused by planting companion plants which
release volatile chemicals which mask the host plant.
• Examples
of Masking
• Peppers
and alliums –alliums (onion crops) as a mask to confuse aphids
• Zucchini
and Nasturtiums – nasturtiums confuse squash bugs
• Tomatoes
and Basil - basil confuses thrips,
armyworm egg laying, hornworm egg laying
• Potatoes
and Tansy or catmint – catmint confuses Colorado potato beetles
• Examples
of Interfering with Egg Laying
Cole crops and Sage, Dill, Chamomile, Hyssop – though these
herbs and flowers are fragrant it has not been proven they repel insects. But
will deter cabbage worms from egg laying.
Also a nectar source to encourage predatory insects
Note: Sage and hyssops are perennials. Cole crops should be
rotated.
Onion and Cole crops with Marigolds – Very little science to
show marigolds effective at repelling pests, but they do reduce egg laying of
onion root fly and cabbage root fly.
• Examples
of Impeding Pest Movement
Physically block pests using:
Hedgerows of closely planted mixed trees, shrubs, perennials
impedes
insect movement
provide
a wind break and shade
also
can provide food for pollinators
Plant low growing cover crops to impede soil pests
also
can improve soil
• Improve
Diversity
Encourages a balanced garden with overall reduction in pests
and disease.
Increases beneficial insects and increases pollinators.
Permaculture/Forest Gardens - Instead of neat rows of monoculture, forest
gardens mix a diverse range of food and non-food producing plants that nourish
each other. They use different nutrients from the soil and make the best use of
space available.
• Increase
Predatory Insects
Intentionally release insects
not
useful unless inside a greenhouse
needs
much study and planning
most
beneficial insects are collected from the wild which
disrupts
the ecosystem of their natural location
Best to encourage native beneficial insects by planting
nectar rich food.
• Examples
of Increasing Beneficial Insects
Dill, Cilantro, Golden Alexander and Fennel (Carrot family)
for aphid eaters, parasitic wasps, ladybugs, lacewings, spiders, soldier
beetles, syrphid flies, damsel bugs and others
Black-eyed Susans and Cosmos for aphid eaters
Aster family plants support many beneficial insects
Carrot (dill, fennel, anise and cilantro) and Mint (sage, marjoram, oregano, lemon
balm, rosemary and thyme) family plants for parasitic wasps who lay eggs on
caterpillars
Crimson Clover – attracts lacewings, mites, minute pirate
bugs to eat thrips. Attracts predatory spiders with its habitat.
• Increase
Pollinators
More pollinators leads to increased harvest
Bumblebees ‘buzz pollinate’ tomatoes
Most pollination is done by native bees versus honey bees
E.g. 250 orchard mason bees can pollinate 1 acre of apple
trees
Versus 15,000-20,000 honey bees
Minnesota has over 400 species of native wild bees
• Examples
to Increase Pollinators
Grow hollow stemmed plants such as Bee Balm and Joe Pye Weed
for pollinators to overwinter
Provide winter shelter by NOT cutting down stalks until
spring when temperatures are in the 50’s. Leave 8-10” of stalk.
Leave open soil and practice no-till gardening to support
ground nesting bees and prevent disturbing brood nests
Plant large, hooded flowers for bumblebees
Plant more squash to attract squash bees which pollinate 80%
of squash. These bees build solitary nests in ground under squash plants, so
tilling disrupts brood nests.
Cosmos, Sunflowers, flowering herbs for sweat bees and other
small native bees
• One
Best Thing To Do
DIVERSITY
• So
What About the ‘Folklore’ in the Beginning?
• Plant
dill next to tomatoes to prevent hornworms
Sort of true. Members of the carrot family (dill, fennel,
anise and cilantro) and the mint family (sage, marjoram, oregano, lemon balm,
rosemary and thyme) provide nectar for special kinds of predatory wasps which
lay their eggs under the skin of certain caterpillars. The larvae then feed on
the host insect. It does not prevent the hornworms, but could possibly kill
them.
• Carrots
love basil
Not proven, but members of the carrot family (dill, fennel,
cilantro) provide nectar for predatory insects that feed on aphids. Note,
carrots don’t flower until the 2nd year.
• Basil
likes tomatoes
This one is true, but not because basil and tomatoes are
BFF! Interplanting basil with tomatoes has been found to help mask tomatoes
from thrips.
• Resources
• Plant
Partners - Jessica Walliser, pub. Dec
2020
• Bringing
Nature Home – Douglas Tallamy
• Pollinators
of Native Plants – Heather Holm
• Attracting
Native Pollinators – Xerces Society
• Joe
Gardener Podcasts - https://joegardener.com/
• Soil
health - https://extension.umn.edu/how-manage-soil-and-nutrients-home-gardens/living-soil-healthy-garden
• Permaculture:
https://midwestpermaculture.com/
Feb 2021
• White
Bear Lake Seed Library
Pam Larson Frink
Blogsite: wblseedlibrary.blogspot.com
Email: wblseedlibrary@gmail.com
