Companion Planting (Allelopathy) is based on the principle that certain plants can attract or repel insects or provide beneficial support to other plants. It can also work the other way around where one plant can be detrimental to anothers growth.
Scientists scoff at the the gardener that practises allelopathy and say that we are wasting our time. However they are quick to mention scientific marvels like the downwind tannin response in Acacia spp when grazed by herbivores.
Think of it a bit like plant body odour, either it's attractive or it's disgusting.... that in a nutshell is companion planting. Some plants have a good BO, others have a great BO and still others are downright disgusting!
This is not a bad thing, one must just learn to work with nature and use the plants to their best advantage.
Below is a comprehensive list of companion plants. Beneficial companions are Listed in Green and Detrimental are bracketed in Red
Apples Chives, nasturtiums, Garlic, Onions (grasses and potatoes)
Apricots Basil, Tansy and garlic (tomatoes)
Asparagus Parsley, basil, lettuce, peppers and tomato
Basil All vegetables and herbs esp, tomatoes, and most fruit trees.
Beans (Runner) Potato, corn, lettuce, eggplant, cucumber, strawberry, celery, carrots, cauliflower, radish and spinach.
(onions, garlic, leeks, chives, fennel)
Beans (Dwarf/Bush) Swiss Chard, beetroot, potatoes (onions, garlic, leeks, chives, fennel)
Beans (Broad) Potatoes, Sweetcorn (onions, garlic, leeks, chives, fennel)
Beetroot Dwarf beans, garlic, chives, onions, lettuce, spinach and swiss chard
Borage Strawberries, tomatoes and lettuce
Brinjals/Eggplants Beans (Runner and Bush), echinacea, peppers and lettuce
Broccoli Onions, echinacea, nasturtiums, leeks and celery (Rue, tomatoes, strawberries)
Brussells Sprouts Potatoes, echinacea, nasturtiums (Rue, tomatoes, strawberries)
Cabbage Beans, beetroot, celery, echinacea, most herbs, onions and potatoes.
(Rue, tomatoes, strawberries)
Carrot Peas, leeks, lettuce, radish, onions, and chives
Cauliflower Celery, beans, echinacea, cabbage, onions and leeks (Rue, tomatoes, strawberries)
Celery Tomato, cauliflower, cabbage, leeks, onions, garlic and beans.
Chamomile Everything, but does really well with Cabbage, Cauliflower, Brussels Sprouts,
broccoli, onions, leeks and chives.
Chervil Dill, coriander, carrots and radish.
Chillies/Peppers Cucumber, echinacea, pumpkins, marrows, lovage, bush beans and lettuce
Chives Parsley, Apples, Carrots, tomatoes, potatoes and brinjals
Coriander Dill, Chervil, Cabbage, Carrots, Broccoli, Brussels sprouts, Cauliflower. (Fennel)
Corn/mielies Lettuce, peppers, pumpkins, cucumber, runner beans and peas
Cucumber Radish, lettuce, beans, peas and artichokes
Dill Carrots, tomatoes, brinjals, peppers, cabbage, fennel and coriander.
Echinacea Peppers, brinjals, tomatoes, potatoes, cabbage, broccoli, brussels sprouts and cauliflower.
Fennel Lettuce, cabbage, broccoli, Brussels sprouts, cauliflower and cucumbers.
(tomatoes, beans, coriander, dill)
Garlic Apples, peaches, nectarines, apricots, almonds, tomatoes and swiss chard.
(Peas, beans, cabbage, strawberries)
Grapes Basil, hyssop, sage and tansy.
Hyssop Cabbage, broccoli, Brussels sprouts, cauliflower.
Kohlrabi Beetroot, swiss chard, leeks, chives and onions.
Leeks Cabbage, celery, onion and celeriac
Lettuce Beetroot, strawberry, radish and corn
Lovage Most plants, but particularly peppers and all beans.
Marrows (All) Parsley, tomato, swiss chard, spinach, squash, corn and capsicum
Melons Corn /mielies and nasturtiums
Mint Cabbage and tomato (parsley)
Nasturtiums Apples, Cabbage, broccoli, Brussels sprouts, cauliflower, kohlrabi, turnips, cucumber,
melons, marrows, pumpkins and radish.
Onion Lettuce, cabbage and carrots
Oregano Strawberries, peppers, beans, cabbage, broccoli, brussels sprouts, cauliflower, kohlrabi and turnips.
Parsley Tomato, asparagus, carrot, strawberries, beans and mint
Peaches Basil, tansy and garlic
Peas Cucumber, radish, turnips, corn, carrots and beans (onions, garlic, leeks, chives)
Peppers/Chillies Cucumber, echinacea, pumpkins, marrows, lovage, bush beans and lettuce
Potatoes Cucumber, sunflower, beans (all), peas and nasturtiums (tomatoes, brinjals, pumpkins)
Pumpkins Corn/mielies and runner beans (potatoes, other pumpkins)
Radish Peas, lettuce and nasturtium
Rue Tomatoes. (Basil)
Sage Carrots, strawberries, grapes, cabbage, broccoli, Brussels sprouts, cauliflower, kohlrabi and turnips
(basil, rue, wormwood)
Savory Tomatoes, beans (all) onions, garlic, leeks, chives.
Shallots Carrots, beetroot and mint
Spinach Strawberry and most plants
Strawberry Borage, lettuce, spinach, swiss chard and bush beans
Swiss Chard Onions, beetroot, cabbage, broccoli, Brussels sprouts, cauliflower, kohlrabi, strawberries and turnips
Tansy Peaches, apricots, almonds, nectarines, cabbage, broccoli, Brussels sprouts, cauliflower, kohlrabi and turnips
Thyme Cabbage, broccoli, Brussels sprouts, cauliflower, kohlrabi and turnips
Tomatoes Asparagus, celery, echinacea, parsley, basil, carrots, onions, garlic, chives and leeks.
(rosemary, potatoes, apricots, peaches, almonds and dill)
Turnips Peas, broad beans and nasturtiums.