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Photo: Patti Moore

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This month . . .


Growing Garden Companions
Promoting Plant Partnerships

Tomatoes and marigolds . . . corn, beans, and squash. Through the ages, gardeners have believed that certain plants prefer particular partners. Don't jump to conclusions; it's not that plants actually like to pal around (a serious misconception)! Rather, some plants appear to do better when grown near others. Arranging crops so they complement each other in some way is known as companion planting. The Three Sisters growing system, long used by many Native American cultures, is one of the most familiar examples.

Scientific research supports some of the claims about which plants make good bedfellows, but many are based on historical observation and tradition. So digging into the science and lore of companion planting can enable your explorers to conduct investigations that break new ground!

If you have limited gardening space, planting companions with different growth rates or requirements can lead to a more fruitful harvest. Some plants provide support or shade that help others thrive. Plants that need lots of nutrients are often paired with those that "feed" lightly. Perhaps the most common reason for companion planting is to prevent pest problems. Specific crops (typically flowers and herbs) are believed to repel certain pests, lure them elsewhere, or confuse them. Others entice beneficial insects, birds, and spiders that have a penchant for dining on problem visitors.

Plants aren't the only ones that benefit from this gardening strategy. A schoolyard landscape featuring a diverse blend of vegetables, flowers, and herbs of varied colors, textures, and aromas can be a work of beauty that engages all who visit. Integrating food plants with ornamental ones is often termed edible landscaping.

Whichever routes you take, the more you mix and mingle plants, the more diverse and resilient a garden system you create. Because such a system better mirrors natural ones, a diverse garden can be an exciting living laboratory for studies across the curriculum. Read on.



Growing Garden Companions

Practicing companion planting can be as simple as tucking a few dill plants into your broccoli bed to entice beneficial insects or transplanting colorful lettuce into a flower border. Here we share some advice and traditions related to three general approaches to companion planting. We encourage you and your students to test some of these ideas and develop your own strategies based on your observations, hunches, and understanding of plant needs. We hope the Curriculum Connections activities offer some inspiration.

Finding Compatible Needs

Plants that have different requirements — for nutrients, sunlight, and space, for instance — often make good garden buddies. Because they are unlikely to compete for resources, you can plant them close together to save space. What's more, some combinations can actually help one or more of the companions flourish. Consider the following factors:

Sunlight — Some plants are sun worshippers and others "relish" respite from the heat (or at least tolerate shade). A clever gardener takes advantage of these differences. Tall crops, such as peas and corn, for instance, can shade lettuce and spinach from the midday sun, extending the harvest season of these cool-weather crops. Consider challenging your students to figure out how to provide shade during a specific time of day (mid-afternoon, for instance.) They'll have to observe where the sun hits the garden at different times so they can decide where to put shade-loving crops in relation to taller ones. Here are some other plants that can tolerate partial shade: alyssum, arugula, beets, broccoli, chard, carrots, cabbage, cukes, lemon balm, lettuce, mint, peas, parsley, parsnips, radish, and spinach.

Nutrients and water — Gardeners often try growing plants with different rooting depths or nutrient needs as companions. All plants need water and nutrients from the soil to survive, but they don't all have the same needs nor do they meet them in the same way. Corn, for instance, is a nitrogen hog, but carrots require much less of that nutrient. Some plants, such as squash, have deep roots that can pull nutrients and water from greater depths than can onions, lettuce, and other shallow-rooted crops. (Your students may want to sacrifice some plants to investigate root types.) A family of crops called legumes, which includes beans, peas, peanuts, lupine, and clover, can actually return more nitrogen to the soil than they consume. This is because they have a symbiotic association with a type of root bacteria that "fixes" nitrogen from the air into a form that plants can use.

Nutrient Needs of Vegetable Plants
Heavy Feeders corn, cukes, eggplants, melons, peppers, sunflowers, tomatoes
Moderate Feeders basil, broccoli (and other cabbage family), lettuce, spinach, Swiss chard
Light Feeders beets, carrots, cilantro, dill, garlic, onions, turnips
Soil improvers beans, lupines, peanuts, peas

Here are some ways you can take advantage of these differences: Plant nutrient-loving cabbage with lighter-feeding onions or garlic, or grow dill (a light-feeder that attracts beneficial insects) in your broccoli bed. Consider growing clover, a legume, between corn rows (once corn is at least six inches high) and turning in the clover that fall or the following spring. You might set up a rotation in which you grow corn in a bed one year and follow it with beans or peas the following year to help restore nutrients used by the corn.

Since plants in the same family tend to have similar needs and can be affected by common diseases and insect pests, it's wise to rotate crops so plant families are not grown in the same bed year after year (see Plant Family Detectives).

Other FactorsSome plants make good partners because their life cycles, growth rates, or temperature preferences differ. For instance, you can plant fast-growing, cool-weather crops like lettuce, radishes, or cilantro early in the season alongside slower-growing, heat-loving tomatoes. You'll be able to harvest your early crops quickly, making room for the tomatoes to take over.


Perplexing Pests


ladybug larvae dine on pesky aphids

It has long been suspected that some plants repel pests, other plants either lure them away from precious crops or merely confuse them, and many plants (particularly herbs and flowers) attract and shelter "beneficial" insects and birds that prey on pests. Pests tend to flourish in a simple environment (with few plant types). The more diversity and variety of plants in your garden the greater will be the number of beneficial organisms that keep a check on the populations of pests. If you want to keep the good guys coming, you'll need to grow a variety of plants with different bloom times.

Some of the following advice on pest-protection partners is based on tradition and other tips are based on scientific research. Students may want to try some companions and observe what happens, or set up "fair tests." Don't be overwhelmed by the possibilities. Consider simplifying your plant decisions by surrounding your garden with an entire border of brilliant and aromatic plants that invite pest predators and parasites and tell would-be plant marauders to scram!

1. Attracting Beneficial Insects (and others)

Many insects, such as small parasitic wasps, green lacewings, and lady beetles, depend on certain pests for nourishment. When pests are in short supply, these do-gooders feed on pollen and nectar. Plants with tiny flowers, such as members of the carrot (umbel family) and daisy (composite or aster) families, are among their favorites. (Most composite flowers, such as the zinnia pictured below, are actually comprised of many tiny flowers, called disk flowers, which grow in the center and surrounding longer, flat ray flowers, which resemble petals.) You can encourage the pest-control squad by mixing the following members of those two plant families with your vegetables: anise, dill, caraway, fennel, yarrow, sweet cicely, zinnia, cosmos, and marigold, or by leaving related weeds (e.g., queen Anne's lace and wild daisies) nearby. Other small-flowered herbs such as thyme and catnip also appeal to these garden helpers. If you devote a section of your vegetable garden to perennial flowers, try coneflower, aster, liatris, coreopsis, and black-eyed Susan. Fruit-bearing trees and shrubs also offer food and shelter to birds, many of which feed on garden pests.

2. Luring Away Pests

Some plants are simply so attractive to pests that you can use them to lure garden intruders away from your precious vegetable crops. (These attractants are referred to as "trap crops.") Once the trap crops are infested with pests, you can pull them out and discard them, pests and all. Try these: nasturtiums for aphids, radishes or nasturtiums for flea beetles, dill and lovage for tomato hornworms, eggplant for potato bugs. Do they really work? Challenge students to conduct tests to find out. They can try the plants listed above or experiment with other plants that seem to be pest magnets.

3. Growing Plants That Offend!

Gardeners have long held that some plants are repugnant to certain pests. (Some of these claims are even supported by scientific studies!) Lots of pests find their way to favorite crops through their sense of smell. It follows that we can also use smelly plants to defend plants! Herbs often exude strong fragrances (from their essential oils) that are believed to repel insects or confound them by disguising the smell of neighboring plants. These aromatic plants include tansy, mint, basil, thyme, and santolina. Gardeners often tuck garlic and onions between other vegetables for the same purpose. Here are some plants thought to repel specific pests:

  • onions for carrot rust flies
  • tansy for colorado potato beetles
  • marigolds and basil for flea beetles on eggplant
  • marigolds for Mexican bean beetles
  • nasturtiums for squash bugs
  • marigolds, mint, or thyme for cabbage moths

Marigolds are one of the flowers most commonly considered to control pests, particularly root-feeding nematodes in soil. Consider sharing with your students that scientists have found that marigolds can, in fact, help control these pests. However, there is a gap between common practice — planting a marigold between tomato plants, for instance — and scientific evidence. Research has shown that the flowers need to be planted very thickly each year and turned into the soil at the end of each growing season in order to affect the nematodes. (This presents another great opportunity for student investigations.) But don't be deterred from growing them; even small numbers of marigolds add vibrance to a garden and may attract helpful insects.

Creating Artistic Edible Landscapes

Some gardens sport vegetables growing in neat rows and flowers blooming in separate beds, with no consorting allowed. In yet other landscapes, flowers, vegetables, and herbs are inextricably mingled because, well, they look so good together! The term edible landscape typically means integrating food plants in ornamental settings. This can be as simple as tucking a few lettuce plants or red chard into that flower bed, or as complex as landscaping an entire schoolyard with an eye toward food production, site diversity, and beauty. In either case, cultivating visually compelling companions can become a design exercise in which your keen observers consider color, textures, height, and form as they decide what to plant where. What's more, it's plain fun! Here are some suggestions to prompt your thinking:

  • Create a border of lettuces, other greens, or parsely interspersed with alyssum.

  • Grow a colorful salad in a small plot or container using pansies, violas, lettuce, calendula, and nasturtiums.

  • Put hot peppers, which often have colorful fruits, in containers or borders. (Some are actually sold as ornamentals and are not edible.)

  • Incorporate herbs that are visually appealing: geraniums, lavender, rosemary, chives, parsley, and lemon thyme.

  • If you use tomatoes ornamentally use determinate or bush types, which are less likely than others to get rangy. (Cherry tomatoes add a nice visual spark.)

  • Ornamental corn and some popcorn varieties are beautifully colored. Plants tend to be shorter than sweet corn and some even have miniature ears.

  • Swiss chard has lovely leaves and the varieties ‘Rhubarb' and ‘Bright Lights' are brilliantly colored. You can cut back leaves that get too large and tattered.

  • Fennel and asparagus both have feathery leaves that mingle well with cosmos flowers and make a nice backdrop for a flower bed.

  • Try growing purple-podded beans on trellises or poles along with morning glories or other flowering vines.

  • Consider the lovely eggplant. It has interesting leaves and its fruits come in lots of shapes and colors: long skinny Japanese types, miniature white "eggs," and lavender Italian varieties, for instance.

The Three Sisters: Age-old Companions

One of the oldest and best-known examples of companion planting is the Three Sisters garden, planted by many Native American cultures. The sisters – corn, beans, and squash – are planted together in such a way that they aid each others' success in different ways. Tall corn stalks provide support for pole beans to climb. Beans, through their symbiotic association with a type of root bacteria, fix nitrogen from the air into a form that plants (especially nitrogen-hungry corn) can use. And large, ground-hugging, prickly squash leaves shade out weeds and may deter critters.



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Copyright© 2003 National Gardening Association

 

Contents

Pg. 1: Growing
Garden Companions

Background

Growing Garden Companions

Finding Compatible Needs

Perplexing Pests

Creating Artistic Edible
Landscapes



Pg. 2: Curriculum Connections

Garden Investigations


Plant Family Detectives

Design an Edible Landscape


Pg. 3: Resources

Web Sites We Like

Books


Related Articles

Cross-grade Buddies Plant Companions

Organic Matters

Pest Patrol

Peas, Beans, and Bacteria

The Three Sisters: Native American Gardening


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