Trap crops lure pests away from other plants and can have a positive effect on our garden even as their roots decompose. Here’s how companion planting and no-dig cleanup can make your garden healthier and easier to maintain.
How Trap Crops Work
Plants are so much smarter than we give them credit for. They’re communicating amongst themselves via electrical, cellular and chemical means all the time.
Thanks to the release of a wide array of Volatile Organic Compounds (VOCs) certain plants can lure pest insects in (called trap cropping) while others release chemicals that happen to mask our favorite crops. Most companion planting practices attempt to confuse the pest before it either eats the host plant or lays eggs on it. Masking a host plant’s own VOC’s from a pest buzzing around looking for food is a pretty powerful organic gardening tool.
There are long-lasting chemical reactions going on below ground as well.
Soil is ‘ground zero’ for the overall health of your garden. Soil is a living breathing thing, full of microorganisms like fungi, invertebrates, worms, bacteria, algae, nematodes and protozoa… up to 1 billion per teaspoon of soil. When we deeply till our gardens we destroy the existing relationships in the soil. These relationships do best when left undisturbed, which is why ‘no dig’ gardening works so well.
We can nurture these relationships and use naturally existing chemical reactions to our garden’s benefit.
Marigolds
Let’s take a well-known companion planting flower, the marigold. They naturally exude a chemical called alpha-terthienyl. This VOC has been shown to mask host plants above ground while repelling root-knot nematodes below ground. Specifically African and French marigolds have been studied and proven effective (Hethelyi et al. 1986; Soule 1993).
First, we should remember there are many kinds of nematodes, some are free-living and feed on many different things in the soil. But, plant-parasitic nematodes cause serious damage, namely the root-knot nematode. They attach themselves to the roots and become part of the plants making them impossible to remove without removing the crop they’ve infested.
By leaving the marigold roots in the soil, the alpha-terthienyl chemical continues to be released as the roots decompose. So, practicing no dig garden clean-up is a win-win. By cutting the plants off at soil level and leaving the roots remaining, you’ll prolong the repelling of the nematodes.
Oats
Oats make a smart choice when cover cropping. As oat plants decompose, they release chemicals that inhibit the germination of seeds by exuding the chemical, Avena fatua. This chemical is one of many that inhibit seed germination in other plants, called allelopathy. You may have heard of alleopathy with Black Walnut trees, as they release juglone, another chemical that inhibits the growth of many other plants. There are many types of allelochemicals, all with their own ways to defend plants against microbial attacks, herbivore predation, and/or competition with other plants. But again, for the oats to keep others out, it’s best if they’re left in the ground.
Building Soil with Companion Planting
Keeping our garden soil covered helps feed the microorganisms, avoids compaction, and decreases evaporation, all ways to build healthy soil. One great way to keep your soil covered is by planting cover crops. My favorite general-purpose cover crop seed mix consists of oats, peas and radishes. This blend gives an all-around nitrogen boost to the soil and creates biomass both above and below the soil surface. And now that we know the oats pack a one-two punch, it makes choosing to cover crop that much smarter.
This article about trap crops was written for Hobby Farms magazine. Click here to subscribe.
