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Soil Symbiosis (The Givers and Takers of the Plant World)

In gardening and agriculture, the relationships between plants and soil are of utmost importance. Some plants improve soil health, while others are particularly demanding and can deplete the soil of certain nutrients if not managed properly.

Plants Beneficial to the Soil:

  1. Legumes (e.g., peas, beans, clover, alfalfa):

    • Nitrogen Fixation: These plants have a symbiotic relationship with specific bacteria (Rhizobium) that live in their root nodules. These bacteria convert atmospheric nitrogen into a form plants can use. When the plants die or when the roots slough off nodules, this nitrogen becomes available to subsequent plants, enriching the soil.

      'Seychelles' green pole beans growing on a red fence

  2. Deep-Rooted Plants (e.g., comfrey, daikon radish, sunflower):

    • Soil Structure and Nutrient Mining: These plants break up compacted soil layers with their long roots, improving aeration and water infiltration. They also bring up nutrients from deeper soil layers, making them available to other plants when their leaves or roots decompose.

  3. Grasses and Grains (e.g., rye, barley, wheat):

    • Erosion Prevention and Organic Matter: Their dense root systems hold soil particles together, preventing erosion. When turned into the soil, they decompose and increase organic matter.

      Dried barley grass grown in a garden
  4. Green Manures (e.g., buckwheat, clover, vetch):

    • Organic Matter and Soil Cover: These are plants grown specifically to be turned into the soil. They provide a protective cover, prevent erosion, suppress weeds, and, when dug into the soil, decompose to increase organic matter and nutrient content.

  5. Target Plants for Pests:

    • Nasturtiums: These act as a trap crop for aphids, diverting them away from other plants. They also attract caterpillars, which may then spare your cabbages and broccoli.

    • Marigolds: While they are known for repelling certain pests, marigolds can also attract spider mites and slugs.

      Beautiful orange and red marigolds

    • Sunflowers: They can act as a trap for stink bugs and aphids, pulling them away from nearby veggies. They are always a favorite of bumblebees, which are an important native pollinator! Some sunflowers are edible, and others are ornamental like these giant red and orange ones:

      Man standing next to tall red sunflowers

    • Dill and Fennel: Both are excellent at attracting tomato hornworms, diverting them away from your tomato plants.

    • Calendula (Pot Marigold): Calendula can be used as a trap crop for aphids, drawing them away from other plants. Additionally, it attracts a variety of beneficial insects such as ladybugs, hoverflies, and predatory beetles.

      Yellow calendula flower with 3 layers of petals

  6. Plants that Attract Beneficial Bugs:

    • Alyssum: Its tiny flowers are ideal for beneficial insects like hoverflies, which are voracious aphid predators.

    • Yarrow: Attracts ladybugs, hoverflies, and parasitic wasps. Ladybugs and hoverflies consume aphids, while parasitic wasps lay eggs in various pests, controlling their populations.

    • Borage: Known to attract predatory insects like parasitic wasps and predatory beetles, it also lures bees to the garden.

    • Carrots, Dill, Parsley, Cilantro (when allowed to flower): These plants are great at bringing in parasitic wasps and flies that control caterpillars and other pests. Look, there's a beneficial hover fly right there!

      Bolted cilantro and parsley flowers attracting a beneficial hover fly

    • Comfrey: This plant not only is a nutrient miner, bringing up nutrients from deep in the soil, but it also supports beneficial bacteria in the soil, enhancing decomposition processes.

    • Mustard and Clover: When tilled into the soil, they can release biofumigants that suppress harmful soil-borne pests and diseases, fostering a healthier soil biome.

    • Lupins: These legumes are known to foster specific beneficial bacteria in their roots, which help in nitrogen fixation.

    • Lavender: Its pleasant aroma attracts beneficial insects like bees and butterflies, but it also repels moths and fleas.

      White lavender next to a leaf with a honey bee

    • Cornflowers (Bachelor's Buttons): These flowers attract a variety of pollinators, including bees and butterflies. Hoverflies, which are predators to aphids, are also drawn to cornflowers.

      Blue and Purple Coneflowers growing in a pot

Nutrient Hogs:

  1. Tomatoes:

    • Tomatoes are heavy feeders that require a lot of nutrients, especially calcium. Insufficient calcium can lead to issues like blossom end rot.
    • Look for organic slow-release tomato nutrients, and make sure it has a lot of calcium. You can also incorporate egg shells into the soil around the base of the tomato plant to slowly release calcium.

      'Stupice' tomato plant producing ripe, red tomatoes
  2. Corn:

  3. Cucurbits (e.g., pumpkins, squash, cucumbers):

    • These plants have extensive growth and large fruits, making them heavy feeders. They require a balanced nutrient intake, especially phosphorus and potassium. These are the last two numbers of the NPK ratio listed on fertilizers.

      Cinderella pumpkin growing on a vine with big leaves

  4. Brassicas (e.g., broccoli, cabbage, cauliflower):

    • These plants require a significant amount of nutrients, particularly nitrogen, for best growth and production.

  5. Berries (e.g., strawberries, blueberries):

    • While they might not be the heaviest feeders in terms of nitrogen, berries have specific pH and nutrient requirements. Blueberries, for example, need acidic soil and can deplete it of certain nutrients over time.

Managing Nutrient Balance:

To maintain a healthy garden, especially when cultivating nutrient-demanding plants, gardeners should:

  • Practice Crop Rotation: This reduces the risk of soil-borne diseases and pest issues, and it helps manage soil nutrient levels by not growing the same nutrient-hungry crops in the same spot year after year.

  • Incorporate Organic Matter: Regularly adding compost, well-rotted manure, or other organic matter can replenish nutrients taken up by plants.

  • Plant Cover Crops: As discussed, certain plants can rejuvenate soil in various ways. After a heavy-feeding plant, consider planting a cover crop that will benefit the soil.

  • Test Soil Regularly: By testing soil every couple of years, gardeners can get an idea of its pH and nutrient levels, allowing for more precise amendments.

By understanding the relationship between plants and soil, gardeners can make informed decisions that promote long-term soil health and garden productivity.

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