Why Companion Planting?
These days, there are so many fertilizers, soil amendments, and other ways to make our gardens thrive using products and chemicals. Historically however, gardeners worked with a much simpler toolkit and one thing they noticed was that plants grown in the presence of certain other plants did better. Specifically, "mono-crops" of the same variety of vegetable, for instance, tended to create a thriving culture of pests, while planting intermittently with other crops actually helped both plants to survive and thrive.
Companion planting simply means arranging your planting locations based on which plants help each other grow, repel pets, or taste better at harvest. It's worth trying because it often makes your garden less work-intensive and helps your plants succeed more without the addition of purchasing garden additions or potentially toxic chemicals.
Qualifications for Companionship
There are a variety of ways that plants can be considered good companions. Here are some traits to consider when deciding what grows together in your yard.
Differences in Height/Root Depth
Plants that grow very high, like corn, are often good companion plants for creeping lower plants that need shade, such as peas. Height differences generally provide support and shade without taking anything away from their companions. This can also be true for plants that draw nutrients from the top inches of soil, versus those that tend to immediately put roots down deep.
Naturally Repelling or Attracting Damaging Pests
When you plant to work on pest control, you can either plant items with, say, a strong scent like mint, which tend to repel insects, or you can plant a popular floral munchie, like nasturtiums, which will attract all the harmful aphids for a feast away from your prize veggies.
Bringing in Beneficial Insects
Other companion plants can encourage the presence of beneficial insects, like ladybugs, because they are known as places those insects like to hang out. When ladybugs are on your companion plants, its not much of a journey for them to eat up all the aphids on the plant you want to protect right next door.
Consider the Impact on Flavor
Blooms and flowers that you may plant together may be done for display or landscaping, but companion planting can also be a way to cultivate flavor. While tomato and basil are known for being helpful for preventing tomato hornworms, many gardeners also report that the tomatoes are more flavorful when they've been planted with basil. Also, your garden bed basically becomes a caprese salad waiting to happen, and that's a true match made in heaven.
Nitrogen or Acidity Additions
Some plants want to be in a nitrogen rich or acidic environment, while other plants are always adding acidity or fixing nitrogen in their roots - why not put those guys together and let them form a beautiful friendship?
Better Than Weeds
Sprawling cover crops tend to work well for standalone plants like sunflowers, since they cover ground that would otherwise be ceded to the weed population. Sunflowers and cucumbers are good friends for this reason; sunflowers aren't stopped by the broad cucumber leaves, but the cucumbers are aggressive enough to take over areas that otherwise might be a weed foothold.
Examples of Great Companion Plants
We've mentioned some of the tried and true companions already, but here are a few more for you to experiment with in your own garden:
Plant flowers like zinnias, marigolds, and cosmos in areas where you want to see an abundance of beneficial insects. For those who want veggies carrots and onions can share a bed, despite both being roots, because of onions cutting down on the amount of rust flies and nematodes.
The "three sisters" gardening method is a three-way companionship of corn, which is grown on by winter squash vines, as well as climbing bean plants. By planting them together, you create the trellis and they all benefit from each other's general biochemical make-up.
Sage, rosemary, and thyme tend to protect from brassica pests so these herbs can act as shield for cabbages, broccoli, brussel sprouts, kale, and kohlrabi
Lavender repels pests that often bother apple trees. Bush beans and spinach both grow fine in the shade of a fairly open corn patch. Note that a corn patch is what it sounds like so don't anticipate industrial-level, super pressed-together corn fields just because of some beans.
Asparagus is a good addition to the above tomato and basil plot since they both naturally aid the asparagus in warding off asparagus beetles, and blueberries do well planted near oaks and pines, which create the acidic soil that helps blueberries thrive.
Bad Companions: Separate These Plants!
There are also plants that combat each other in the garden, trying to get the same resources and resulting in depleted resources for both plants. Garlic and onions, for instance, just don't work in the area where beans and peas are trying to grow. Cabbages and cauliflower need their own corners of the garden, as do beans and potatoes. If you notice that a particular plant does much more poorly this year than it did in the past, record the names of its neighbors and make a note to find a new spot for that plant in the following year.
In general though, the information above will help you get your garden off to a good start just by creatively locating your plants!