There is a lot of science as well as traditional practices involved in companion planting.
There are many reasons certain combinations of plants are traditionally grown together. Sometimes there is a physical environment benefit, sometimes a nutritional benefit or a natural pest deterrent. There are also plants that can have negative effects on each other. To get the most from your edible garden it is helpful to gain an understanding of companion planting. After choosing the edibles you will grow, determine which grow well together as well as non edible companions that are beneficial.
Mutual advantages are produced in a number of different ways. Some plants naturally produce chemicals that can negatively impact plants and organisms. The actually effect can sometimes be a benefit to the plants you grow. For example Marigolds are commonly grown to produce thiophenes that deter nematodes that attack plant roots. Normally we think of the negative impacts of Walnut trees producing toxins that prevent plants from growing. Plants that produce biochemicals influencing growth and reproduction of other plants and organisms are called allelopathic plants.
Plants are so amazing, they can also create changes in the soil nutrition! Sometimes by adding biochemicals that benefit neighboring plants’ growth, flavor or yield. Sometimes by taking up something from the soil that might create bitterness or negative flavors for certain edibles.
Physical and environmental benefits are easy to identify. A tall sturdy plant may provide support for vining plants. A leafy plan can provide relief from hot afternoon sun for more shade loving plants. Tall plants grow happily behind short ones while both enjoying plenty of sunshine. Vining edibles scramble all over the garden to suppress weeds.
Color and scent are often used by plants to either attract or repel insects. Specific plants can be used to attract pollinators and other beneficial insects. Others are used to repel damaging pests. Even just providing a natural habitat for beneficial insects is not only helpful but can add visual interest, color and beauty to your garden.
Companion planting is a great way to add biodiversity to your garden and sustainable practices by reducing the need for chemical additives and pesticides. There is a ton of information out there, so start simply by researching benefits to a couple of your favorite plants, or better yet, troublesome plants!
Just some of the common beneficial companion pairings:
Basil and Tomatoes - basil will improve tomato flavor and produce larger fruits. The basil will also deter aphids and fruit flies to aide the tomatoes.
Bee Balm and Tomatoes - bee balm improves growth and flavor
Asparagus and Tomatoes - the tomatoes produce solanine that deters the asparagus beetle. The asparagus produces asparagin that repels nematodes.
Beans and Corn - corn is a heavy nitrogen user, beans replace the nitrogen when they die back at end of season.
Carrots and Rosemary - rosemary will repel the carrot fly
Borage and Tomatoes - also borage and strawberries, squash, and anything else that cabbage worms and hornworms attack. Borage deters them as well as attracting bees.
Strawberries and Lavender - lavender will help deter the birds
Radishes and Cucumbers - radish deters the cucumber beetle
Radishes and Spinach - large radish leaves shade young spinach
Horseradish and Potatoes - horseradish will help make the potatoes disease resistant and deter the potato beetle
Horseradish and Apples - horseradish will help the apples with brown rot, powdery mildew and fungus
Garlic and Roses - the garlic will deter Japanese beetles
Dill and Cabbage - dill improve the growth and health of cabbage
Radish and Chervil - chervil makes the radishes hot if you like them hot
Radish and Nasturtium - nasturtium will improve the radish flavor
Hyssop Agastache and grapevines - hyssop will increase the grape yield
Marigolds and everything - scented marigolds deter all manner of garden pests and stimulate vegetable growth
Marjoram and everything - marjoram stimulates vegetable growth
Tarragon and everything - tarragon will improve flavor and growth of vegetables
Onions and Parsnips - onions keep the root maggots away
Plant pairings with negative effects:
Basil and Raspberries - basil may inhibit fruiting of the raspberries
Strawberries and Brussels Sprouts - these two retard each others’ growth.
Strawberries and Cauliflower - strawberries will inhibit cauliflower growth
Tomatoes and Cauliflower - tomatoes also inhibit cauliflower growth
Dill and Fennel - these may cross pollinate
Hyssop Agastache and Cabbage - the hyssop will attract cabbage butterfly
Hyssop Agastache and Radish - hyssop will stunt radish growth
You will find that certain plants, such as borage and beans, like and improve just about anything they grow with. Nothing really seems to like growing with fennel. In some cases scientific evidence may not exist for good pairings, but obvious physical benefits or hundreds of years of simple observation is enough proof for most gardeners.