Master Gardeners - Companion planting: Where you put those plants matters, too - Yakima Herald-Republic

Companion planting can help you grow healthier and more productive plants without harsh pesticides and synthetic fertilizers.

This gardening technique has been used for generations to naturally boost plant health and reduce pest activity in garden spaces, herb beds and container gardens. Try some of the top companion plant pairings listed below in your garden this year to get your best harvest yet.

It doesn't just matter what plants you grow, it matters where you plant them. Companion planting works by pairing the right plants in garden beds to enhance the growth of one or both plants.

Companion plants are plants that benefit each other in at least one way. Those benefits can include natural pest control, increased pollinator activity, improved plant and soil health, added shade and support, weed suppression and better disease resistance.

One of the classic examples of companion planting is the Three Sisters, which was developed by Native American cultures centuries ago. In this companion plant pairing, corn, squash and climbing beans are interplanted to enhance the growth of each other. The corn provides support to the beans, the beans boost soil nutrients due to their nitrogen-fixing abilities, and squash's large leaves shade the soil to conserve moisture and block weeds.

The Three Sisters is just one example of companion planting, although there are many more. This gardening technique has gained popularity in recent years, as there have been more scientific studies conducted to find the best tried-and-true companion plant pairs. You'll find the results of these studies in the tips below.

Use herbs to repel pests

Many pest insects avoid strongly scented herbs and other plants. Interplanting scented plants among your vegetables can naturally repel many insects and can even keep deer and other plant-eating creatures out of your garden beds. Try these aromatic plants to naturally repel pests:

• Garlic and other alliums: Repels deer, slugs, caterpillars and Japanese beetles.

• Mint: Repels flea beetles, moths and aphids.

• Sage: Repels cabbage moths and carrot flies.

• Tansy: Repels ants, beetles and several other flying insects.

• Rosemary: Repels cabbage loopers, carrot flies and bean beetles.

Additionally, in order to prevent disease and pest spread, avoid planting similar plant species together. For example, peppers, tomatoes and other nightshades can be vulnerable to the same pests, and they should be spaced apart in your garden, and crop rotation should occur.

Interplant with flowers

In the past, companion planting mostly focused on the benefits that different vegetable plants can provide to each other when planted together. However, more recent studies have found that ornamental flowers and flowering herbs can be some of the best species for companion planting.

Flowering herbs, such as dill, sage and chives, are extremely attractive to bees and other pollinators. Choosing to grow these herbs among your vegetables can increase pollinator activity and boost harvest yields of fruiting plants like squash and cucumbers.

Attract beneficial insects

Just as flowering plants attract pollinators, they can also boost the activity of other beneficial insects in your garden. These beneficial insects will feed on pests and reduce the need to use harsh pesticides.

Plants like cosmos, calendula and marigolds can attract parasitic wasps and hoverflies that feed on cabbage loopers and other pests. These plants can be helpful when growing broccoli, cauliflower and other brassicas, which are often targeted by caterpillars.

If you're struggling with aphids, dill, alyssum and coriander can attract ladybugs to keep aphid populations in check.

Improve garden soil

Legumes such as beans and peas are well known for their nitrogen-fixing abilities, which naturally improve garden soil and reduce the need for fertilizers. Interplanting legumes with other vegetables can help your plants grow healthier and faster. As nitrogen is particularly useful for leaf development, planting legumes with leafy greens can help you grow lusher leaves. Some other top companion plants for legumes include carrots, corn, turnips, strawberries and beets.

Shelter from too much sun

While most vegetables and herbs prefer to grow in full sun, if you live in a hot area, some plants may suffer from sunburn during the heat of summer. Companion planting can help you avoid this. To protect tender plants, try growing larger, leafy plants above them to provide shelter and shade during the heat of the day. For example, companion planting tomatoes with basil will help shield basil leaves from the bright sun and prevent leaf scorching. In return, basil appears to reduce some pest and disease problems for tomatoes.

Control weeds

Large leaves can shelter plants from the sun, but they do more than that. Interplanting garden beds with leafy greens and other plants with large leaves can help keep your garden soil covered. This in turn will naturally suppress weed growth and reduce the need for weed killers. Additionally, cover the soil not only with mulch but with leafy plants that can also slow down evaporation rates and help regulate moisture levels for nearby plants — which is the same principle as using mulch.

Sow fast growers

Plants like tomatoes, squash and cucumbers can be slow-growing, and you may need to wait several months to harvest. To maximize your garden space, try companion planting fast-growing vegetables among your long-season crops. Plants such as carrots, radishes and lettuce will often grow fast enough that you can get a harvest or two in before your tomatoes mature.

For any gardening questions, you are always welcome to contact our Master Gardener Clinic at 509-574-1604 or email gardener@co.yakima.wa.us.