There is a helpful chart here to learn more about specific crops that grow well together! And, some other great information here
Think about Height/ Sun:
Tall, sun loving plants like tomatoes can share space with shorter plants that prefer shade, such as lettuce and basil. When it gets too hot for greens, taller plants start growing & provide shade for the greens.
Really tall crops like sunflowers can also shade out other crops, so think about where you place them in relation to the sun, and plan accordingly.
Protection - Tall, dense plants can shade or provide a windbreak for more sensitive plants.
Vertical growing - Trellising plants can create more space for other plants to grow. Getting plants off the ground will also pest damage & diseas
Grow plants that grow above ground and those that grow below ground next to one another
Maximize space by giving crops space to grow! Examples include planting your carrots near tomatoes, or plant beans next to potatoes.
photo credit: coffee for roses
Natural Pest Control
Repellents - Some plants, like marigolds, release scents or natural pesticides that can help repel many common garden pests.
The natural properties of some plants help keep pests away fromothers (e.g. corn & squash are often planted together as the prickly vines of the squash can help deter animals & bugs, and climbing
squashes are less susceptible to insect damage.)
Trap Cropping - Some people use ‘sacrifice plants’ to attract pests away from vulnerable plants (e.g. collard greens attract black moth away from cabbage).
Attract beneficial insects - Some plants provide a desirable habitat for insects that will help balance populations of damaging insects. Bring the good bugs into your gardens with a diversity of crops
Improve Soil Quality
Symbiotic Nitrogen Fixing - Peas, beans & clover have the ability to fix nitrogen in the soil for their own uses & to the benefit of neighbouring plants (e.g. Beans are nitrogen fixers, while potatoes are heavy nitrogen feeders, so they grow great next to one another!)
What Tastes Good Together Often Grows Well Together!
Some crops such as basil and tomatoes are great companion planting matches. Basil doesn't take up much space and can grow around the tomatoes, and some people say basil growing nearby makes tomatoes taste sweeter!
Another great example is cucumber and dill, the cucumber will spawl out on the ground or grow up on a trellis, while the dill is tall and skinny and can grow amongst the vines. And, they make a great team when making pickles or summer salads!
Check out our whole Garden Planning Series here!