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
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