Gathered here for easy future reference:
Anise
Plant anise and coriander seeds together. They will both germinate more quickly. Keep soil moist and separate when seedlings have grown a little.
Apple
If planted with chives there is less chance of apple scab disease.
Asparagus
Becomes more vigorous if planted with parsley.
Basil
Basil repels white fly and makes a good companion to tomatoes, in the garden & the kitchen. Use 3 basil plants to each tomato plant. Basil also repels flies and mosquitoes, so useful in kitchen, outdoor barbecues. Don’t plant near rue. Deters tomato hornworm, aphids, flies and mosquitoes. Slows growth of milkweed bugs and acts as a fungicide.
Beans
Less likely to suffer from beetles if petunias also planted alongside. Grow more strongly if planted with summer savoury.
Bad Companions: Basil, Beets, Cabbage, Fennel, Kohlrabi, Onion, Radish, Sunflower
Beans (Bush)
Plant with sunflowers, they like partial shade and the sunflowers attract birds and bees. All bean types are beneficial if planted with cucumbers, potatoes, corn, celery, savoury because these plants are heavy feeders. Beans create their own nitrogen and are light feeders.
Bad Companions: Basil, Fennel, Kohlrabi, Onion
Bee/Lemon Balm
Plant with tomatoes, it improves growth and flavour.
Beetroot
Grow better if planted with onions, kohl rabi, basil, beans, lettuce, cabbage and tomatoes. Planting with onions helps deter some insects and deters weeds.
Bad Companions: Mustard, Pole Bean
Bergamot
Attracts beneficial honey bees.
Borage
Plant with strawberries to increase crop. Also good with tomatoes and squash. Attracts bees to the garden. Deters tomato worms, attracts bees, helps growth and flavour.
Broccoli
Planted with dill or mint grows better.
Cabbage family
Cabbage butterfly is repelled by planting rosemary or sage with cabbages. Any member of the cabbage family should also be planted with potatoes, tomatoes, celery, dill, chamomile, sage, thyme, mint, rosemary, lavender, beetroot or onions. All the above are aromatic plants, and therefore deter cabbage worms. Thyme and tomatoes also help control flea beetles.
Bad Companions: Pole Bean, Strawberry, Tomato
Calendula (Pot Marigold)
If planted with tomatoes, this repels asparagus beetles, tomato worms and other pests.
Caraway
Long roots help break down and condition heavy soils, can plant near shallow rooted plants. Dislikes fennel. Attracts parasitic beneficial wasps. Caraway dislikes being planted near fennel. Sown with peas, caraway seeds germinate more easily.
Carrots
Carrot fly is repelled if carrots are planted with sage or onions. Also plant with peas, lettuce, chives, leeks, rosemary or tomatoes.
Bad Companions: Celery, Dill, Parsnip
Catnip
Planted on the vegetable garden border, catnip will deter cats from venturing further. Protects against flea beetles, and attracts bees.
Celery
Planted with bush beans, they help each other to grow better. Also good companion with leeks, tomatoes, cabbage and cauliflower.
Bad Companions: Carrot, Parsley, Parsnip
Chamomile
Compatible with onions and cabbages but don’t plant too much. Chamomile tea, made by soaking blossoms in cold water for 1 to 2 days, is excellent spray for damping off. Improves both growth and flavour of onions and cabbages.
Chervil
Chervil improves flavour of carrots if grown with them. Radishes planted near chervil has hotter taste, and improved growth.
Chives
Carrots grow larger planted near chives. Helps prevent apple scab if grown underneath apple trees. Also helps control aphids and black spot on roses. Cooled chive tea made from chopped chives in boiling water helps combat downy and powdery mildew.
Comfrey
Comfrey keeps surrounding soil rich and moist. Rotted leaves and roots mixed with water makes good fertiliser. Improves size and flavour of strawberries if planted nearby.
Coriander
Sown with anise seeds aids germination in both. Coriander repels aphids. Don’t grow near fennel as it hinders its seed formation.
Corn
Sowing with beans or peas provides an increased nitrogen supply to the corn (if corn and peas/beans are planted in alternate rows). If sunflowers are planted with corn, the incidence of armyworm decreases. Also plant with potatoes, cucumbers, pumpkin, squash. Vining things like this shade the ground, keeping weeds down, and use the corn stalks to trail up on.
Bad Companions: Tomato
Cucumbers
Plant with beans, corn, peas, radishes, and sunflowers.
Bad Companions: Potato
Dandelion
Plant along garden border to produce pollen for lady beetles, lacewings, and other predators and parasites. Repels Colorado Potato Beetles.
Dill
Cabbage grows well planted near dill. So does lettuce, corn & cucumber. If dill is allowed to flower it suppresses the carrot crop, if not allowed to flower it is fine. Don’t plant near fennel as they may cross fertilise.
Eggplant
If planted with aramanthus, there is less likelihood of insects on the eggplant. Also, beans planted with eggplants repel beetles which would otherwise attack the eggplant.
Bad Companions: Fennel
Elderberry
Plant near your compost heap as it assists in breakdown. Humus from base of elderberries make excellent topsoil.
Fennel
Don’t grow fennel in the vegetable garden. It is hated by tomatoes, kohlrabi, caraway and wormwood. If planted near dill may cross fertilise. Repels fleas, so grow it around dog kennel.
Garlic
Planted near roses keeps aphids away. If grown around fruit trees effective against borers. Protects peach tree from leaf curl and apple trees from apple scab. Grown near tomatoes deters red spider mites. However peas, beans, cabbages and strawberries hate it. Garlic spray may be made by crushing 4 cloves and steeping in a litre of water for several days as an insecticide for vegetables and flowers.
Geranium
Plant near roses, grapes and corn. Repels cabbage worm. Oil of geranium prevents red spider mite.
Grapes
Planting clover increases the soil fertility for grapes. Hyssop likewise increases the vine crop.
Horseradish
Helps deter potato bug if planted near potatoes. Can take over so keep restricted.
Hyssop
Good for cabbages and grapes. Helps deter white butterflies. Good insect repellent if planted in vegetable or flower garden. Keep away from radishes.
Lavender
Attracts butterflies. Lavender bags repel mice, ticks and moths.
Leeks
Leeks grow better if planted with carrots, celery or onions.
Lemon Balm
Attracts bees. Improves growth and flavour of tomatoes.
Lettuce
Plant with carrots, radishes, strawberries or peas.
Lovage
All round garden helper. Improves health and flavour of most plants near it.
Marigolds
Plant everywhere! Deter many insects and slugs.
Marjoram
Beneficial on most vegetables planted near it.
Melons
Plant with corn, nasturtiums, and radishes.
Bad Companions: Potato
Mint
Repels cabbage butterfly, grow near cabbage family or tomatoes. Repels fleas, ants and mice. Keep mint and parsley away from each other.
Nasturtium
Useful insect repellent. Plant around broccoli, cauliflower, cabbage family, radishes, tomatoes, cucumbers and fruit trees. Deters white flies, squash bugs, and are a trap crop for aphids. Limits wooly aphid damage to apple trees if planted in a circle around them. Get more tips from Tree service experts.
Onion
Planting chamomile with onions improves the flavour of the onions.
Bad Companions: Asparagus, Beans, Peas, Sage
Oregano
Plant near broccoli, cabbage and cauliflower to repel cabbage butterfly and near cucumbers to repel cucumber beetle. Also benefits grapes.
Parsley
Grow near chives, but away from mint. Aids growth of roses, tomatoes, asparagus and carrots.
Peaches
Growing garlic around peach trees reduces the chance of peach leaf curl disease.
Peas
Grow them almost everywhere, peas add nitrogen to soil. Growing interplanted with corn enhances growth of the corn.
Bad Companions: Onion, Late Potato
Peanuts
If grown with squash or corn will increase the yield.
Potatoes
Plant horseradishes with potatoes to make them more disease resistant.
Bad Companions: Cucumber, Kohlrabi, Parsnip, Pumpkin, Rutabaga, Squash family, Sunflower, Turnip, Fennel
Pumpkins
Plant with datura to increase the vigour and health of the pumpkins. Also plant with corn.
Radish
Plant with climbing beans, and both grow better. Plant with lettuces, and the radishes become more succulent in summer time. Also plant with peas, nasturtiums and cucumbers. Deters cucumber beetle and other insects.
Bad Companions: Hyssop
Rose
Planting chives or garlic with roses protects them from black spot and some pests, including aphids. Parsley protects roses from beetles. Though the effects of the above-mentioned plants are not that powerful in the house or flat, give preference to EZ Bed Bug Exterminator NYC.
Rosemary
Grows well with sage, improves growth of carrots, cabbage and beans. Don’t grow near potatoes.
Rue
Hates basil. Plant near roses, strawberries and fig trees. Effective fly repellent and it repels dogs and cats which hate it.
Sage
Plant near rosemary. Good grown with cabbage and carrots, peas and beans. Keep away from cucumbers. Sage tea can be sprayed on mature plants not seedlings.
Salad Burnet
Good with thyme and mint.
Savoury(Summer)
Grow near onions and beans. Deters bean beetles.
Savoury(Winter)
Useful insect repellent.
Spinach
Plant with strawberries, and base of trellised peas. Spinach benefits from shading of peas and wind protection.
Squash
Plant with corn or nasturtiums.
Strawberries
Planted with borage improves the soil nutrition for the strawberries. Also plant with bush beans, spinach and lettuce. Do NOT plant with tomatoes.
Bad Companions: Cabbage, Potato
Tansy
Repels ants, flies and moths. Rub leaves onto fur of dogs and cats to repel fleas. Plant near fruit trees and roses. It concentrates potassium in the soil so good for compost heap.
Tarragon
All purpose garden helper.
Thyme
Attracts bees and deters cabbage worm so plant near members of cabbage family. Beneficial effect on plants near it.
Tomatoes
Tomatoes grow and produce better when planted with marigolds; the same rule applies to basil planted with tomatoes.
Bad Companions: Pole beans, Corn Dill, Fennel, Potato
Valerian
Excellent addition to compost heap as stimulates phosphorous activity in soil. Earthworms love it.
Wormwood
Grow by itself edge of garden as inhibits growth of other plants. Spray discourages slugs and snails.
Yarrow
Increases essential oil content enhancing aromatic quality and making more resistant to insect attack.
And, VERY IMPORTANT: Interplant herbs and flowers. By planting flowers and herbs among your vegetables, you can attract beneficial insects and birds, which are natural predators to those pests that eat your brassica leaves. Flowers and herbs can also confuse pests and deter them from finding your prize crop. If you have problems with pest infestation, then you may consider hiring professional pest control services.
But wait, it gets better. Here’s a list of herbs and the pests they repel:
Basil
Flies, Mosquitoes
Borage
Tomato Worm
Catnip
Flea Beetle, Ants
Coriander
Aphids
Dead Nettle
Potato Bug
Feverfew
attracts aphids away from other plants
Flax
Potato Bug
Garlic
Japanese Beetle, Aphids
Horseradish
Potato Bug
Henbit
Insect Repellent
Hyssop
Cabbage Moth
Lavender
Moths
Marigolds
Mexican Bean Beetles, Nematodes, others
Mint
Cabbage Moth, aphids, flea beetles
Nasturtium
Aphids, Squash Bugs, Striped Pumpkin Beetle
Pennyroyal
Flies, Mosquitoes, Fleas, others
Pot Marigold
Tomato Worm, Asparagus Beetles, others
Pyrethrums
Dried flower, repels insects
Rosemary
Cabbage Moth, Bean Beetle, Carrot Fly
Rue
Japanese Beetles
Sage
Cabbage Moth, Carrot Fly, Flea Beetle, Slugs
Southernwood
Cabbage Moth
Summer Savory
Bean Beetles
Tansy
Flying Insects, Japanese Beetles, Striped Cucumber Beetles, Squash Bugs, Ants, Flies
Thyme
Cabbage Worm
Wormwood
Plant as a border to repel animals