What is Companion Planting?

Companion planting is one of the more mysterious parts of gardening, even for the most advanced grower. When you initially research companion planting, you’ll find a wide range of information all with different focuses. Some information is extremely detailed and based on scientific research, while other information is much more esoteric and based on anecdotal evidence only.

While we don’t discourage either method in finding information on companion planting, it can be quite overwhelming for those beginning in gardening. In this blog, we’ll focus on the basic question of what is companion planting and how to make it easier to implement in your garden.

When planting our crops each year, we’re always sure to include a wide range of flowers, vegetables, and herbs as companion plants to one another. This simple act of planting a wide range and variety helps to support a diverse insect population, balances the threat of diseases, and makes your garden more likely to thrive through the whole season.

When considering what is companion planting, remember that this term is very broad and encompasses more specific growing like polyculture and intercropping. No matter what you call it, companion planting has a host of benefits including:

• Reduced pest pressure
• Weed management
• Reduced disease pressure
• Improved soil structure or fertility
• Improved pollination
• Improved insect populations, which helps with biological controls

When selecting companion plants for your garden, start by considering whether they might hinder each other’s growth or productivity. This can occur due to various factors, such as differing irrigation requirements. For instance, if one plant needs to be deprived of water for a period (like garlic during curing), while another requires consistent watering, they may not complement each other well. Also, factors like height and growth habits should be considered. Avoid pairing plants that may overshadow or impede each other’s access to sunlight.

For example, planting aggressive pumpkin vines alongside delicate marigolds could result in the marigolds being overwhelmed by the vigorous growth of the pumpkins. Therefore, always evaluate whether planting certain crops together might cause harm to one another.

The second deciding factor when considering companion planting is whether the companion plantings will benefit the garden with diversity. The answer to this is almost always yes. The more diverse crops you have in your garden, the happier it is!

This situation can be particularly problematic when one crop is highly susceptible to a specific pathogen. For example, growing zucchini that is susceptible to powdery mildew, which would not be a good fit under your roses. Your zucchini will invariably get powdery mildew and that will be a host plant to pass to your roses. (Also, imagine how unenjoyable it would be to harvest near those thorny roses!)

In this example, a better companion crop for zucchinis would be zinnias – these tall and beautiful flowers would look beautiful in between your zucchini plants. Similarly, both crops like to be watered at the soil level and will grow beautifully together.

While the list of companion plantings can be extensive, and we’re constantly uncovering new ones (thanks to technological advances), here are some tried-and-true plant partners that have mutually beneficial relationships.

Cover Crops or Green Manures

Cover crops or green manures are considered companion plantings because they improve the fertility and the tilth or texture of your soil. Here at San Diego Seed Company, we plant cover crops each year on the farm and notice a big difference within just one season! Crops like oats, buckwheat, clover, cowpeas, and favas (like our organic favas, or our crimson red flowered favas) are great choices for cover cropping. Cover crops help in drawing up nutrients that are lower in the soil, adding organic matter and improving soil structure and drainage.

Trellising with Plant Partners

For as long as we have been gardening, growers have seen the benefits of using an existing plant as a trellis. Here are some interesting companion plants that work well together to physically support one another.

• Sunflowers and climbing beans
• Corn and pole beans
• Okra and cherry tomatoes
• Tree kale and vining spinach

Of course, these are just to name a few. Let your imagination give you more ideas in the garden!

Using Companion Planting to Deter Pests

One of the top reasons people opt for companion planting is the idea that it can help keep pests at bay. Research has backed this theory with many plant pairings, but here are a few of our favorites.

• Radishes and pac choi can be planted with various vegetables to help lure flea beetles.
• Mustard greens will lure harlequin bugs from various crops. Plant them as a trap crop.
• Nasturtiums will lure squash bugs from zucchini plants.
• Basil can help deter thrips from your tomatoes.
• Interplant calendula with collard greens and other greens to reduce the prevalence of aphids.
• Plant hyssop, sage, dill or chamomile to reduce the number of eggs laid on your cole crops from cabbage worm butterflies.
• Allow your dill, cilantro, and parsley to flower to attract beneficial insects.
• Plant sweet alyssum to attract parasitic wasps that help with pest control.

These are just a few of the many proven companion planting partnerships that exist. If you are ever in doubt, remember that the best thing for your garden is always diversity. A diverse garden will provide the wide range of plant matter needed to support the pollinators and insects needed for a thriving garden!