Anti-Microbial Companion Plants
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When caring for plants and animals, I prefer to focus on supporting their overall vitality and health, as opposed to worrying about or focusing on disease.
There is an inherent healing ability across all species, and ensuring a healthy environment and supporting optimal hydration and nourishment go a long way toward helping ensure optimal vitality and resiliency, including the ability to recover from afflictions.
Fortunately, there are many options when it comes to naturally supporting the resilience of our crops. For example:
- diversity – Generally, the more ecologically diverse an area, the more the incumbent plants are able to withstand stresses, whether biotic (animals, bacteria, fungi) or abiotic (drought, heat, etc.).
- perennial plants – The presence of trees and perennial plants (and/or cover crops where the roots are left intact in the soil) allow mycorrhizal populations to build in the soil, assisting plants in accumulating nutrients and water, increasing resilience and the ability to better withstand stresses.
- natural nutrients/ compost – Plants have a symbiotic relationship animals (including us), and with each other . Various plants accumulate an assortment of nutrients, which can support surrounding plants in their health and growth. Mulching with these nutrient-accumulating plants or composting them and using the compost as natural fertilizer is a wonderful way to naturally nourish plants. And while varying results can occur, a very large greenhouse-based grower reported that his fertilizer, fungicide, and insecticide costs went from $1,700/ week to $17/week when he converted to organic methods using compost teas, and his results were better! Many case studies show similar, favorable results. This is not surprising, given the extensive beneficial compounds found in plants and the universal, mediumistic properties of water.
And research indicates that certain natural compounds from plants can be especially helpful in inhibiting microbial infections in crops. Here are just a few examples:
- Silica has been shown to aid plants in multiple ways (see more below*1). Silica is found in the highest amounts in nuts, parsley leaves (Petroselinum crispum), Brassica roots (Brassica spp.), wild thicket bean fruits (Phaseolus vulgaris, native*), cucumber fruit (Cucumis sativus), spinach leaves (Spinacea oleracea), lettuce leaves (Lactuca sativa, native), dill plant (Anethum graveolens), nettle leaves (Urtica dioica, native), horsetail aerial parts (Equisetum arvense, native, careful: please see “Horsetail notes”, below*2), and oat straw (Avena sativa). *Here, “native” refers to the east, north-central Midwest
- Salicin/ salicylic acid, a compound primarily found in the inner bark of willows (Salix spp., with over a dozen native species), has been shown to help reduce apple scab and other diseases. Mulching with trimmings could conceivably help reduce infections in surrounding plants over time as rains leach the compound into the surrounding soil. Creating “willow water” (soaking willow trimmings in water for a few days and using to irrigate plants) can be especially effective. Poplar trees also contain some similar compounds (including eastern cottonwood (Populus deltoides, native), as do meadowsweet flowers, leaves & roots (Filipendula ulmaria), and wintergreen leaves (Gaultheria procumbens, native).
- Thymol, a compound in various plants including thyme (Thymus spp.), oregano (Origanum spp.), bergamot/ bee balm (Monarda spp., 5 native species), and savory (Satureja spp.), has displayed significant anti-microbial properties, including anti-bacterial (A-B), anti-fungal (A-F), and anti-viral (A-V).
- Sulfurs, compounds in many Allium and Sinapsis and Brassica species, are star anti-microbial compounds (more below).
- Tannins, water-soluble compounds in many plants, have shown promise in blocking the growth of harmful fungi. Many nuts and unripe fruits have tannins, designed to protect them from herbivores, insects, birds, and pathogens. Soaking nuts in several changes of water to reduce tannins is a common practice prior to ingestion (especially with acorns). Consider using that diluted soaking water to hydrate vulnerable plants, possibly (up to you) exercising caution and testing just a small area initially and observing the results.
Further, some specific plants offer various anti-microbial properties that can potentially help control pathogenic organisms around crops. Some have been specifically tested against plant microbes, while others generally show anti-microbial properties and are believed to provide some benefit.
Some of these plants can be intercropped (depending on your situation), or added to compost, or “chopped and dropped” and used as mulch. For small planting areas, some of these plants can be grown in containers and moved around as needed: [note: “ ~ “ = approximately]
- alliums (Allium spp., including 5 natives: wild leek (Allium burdickii), meadow garlic ( canadense), nodding onion (A. cernuum), wild chives (A. schoenoprasum) and ramps (A. tricoccum)) display a variety of anti-microbial properties, with onions mostly being anti-bacterial (A-B), and chives and garlic being anti-fungal (A-F), A-B, and anti-viral (A-V); chives have also been shown to prevent scab (ideal when made into a “tea” and used as foliar spray)
- basil (Ocimum spp.): A-B, A-V
- burdock (Arctium lappa) has compounds shown to deter downy mildew (from oomycetes in cool, moist conditions)
- garlic (Allium sativum) has sulfur compounds that have been shown to reduce downy and powdery mildew (fungi, in warm, dry environments), as well as botrytis (gray mold/ fungal), moniliosis (fungal, primarily affecting stone fruits), rust (fungal), etc.
- chamomile (Matricaria chamomilla) has displayed some activity against certain fungi and scab (caused by bacteria or fungi that can lead to lesions, primarily on potatoes and apples); making an anti-fungal spray by soaking blossoms in cold water for a couple days can be used as a foliar treatment to control damping-off (caused by fungi and water molds) in greenhouses & cold frames
- wild cherry (Prunus serotina): A-B, A-V
- cilantro (Coriandrum sativum) has been shown to be specifically effective against the fungi Aspergillus niger and Fusarium oxysporum
- dill (Anethum graveolens): A-B, A-F, A-V
- elderberry (Sambucus spp.): A-B, A-V
- fennel (Foeniculum vulgare): A-B, A-F
- fenugreek (Trigonella foenum) was demonstrated to be effective against the fungus Aspergillus niger
- goldenseal (Hydrastis canadensis): A-B, A-F
- horseradish (Armoracia rusticana) contains sulfur compounds that help deter moniliosis
- horsetail (Equisetum arvense), with its high silica content*1, has been shown to help reduce bacteriosis, botrytis, damping off, downy and powdery mildew, moniliosis, rust, and scab; please see additional plants that are rich in silica near the top of this article; careful! please see “Horsetail notes”, below*2
- lemon balm (Melissa officinalis): A-B, A-V
- marshmallow root (Althaea officinalis): A-B
- mullein (Verbascum thapsus): A-B, A-V
- mustards (white: Sinapsis alba, brown: Brassica juncea, and yellow: Brassica napus), with their high glucosinolates, have been shown to help control soil born pathogens (fungi) and nematodes when mixed into the soil as a pre-planting treatment
- nasturtiums (Nasturtium officinale) have been shown to reduce cankers (caused by fungi or bacteria) and powdery mildew
- nettle (Urtica dioica), with its high silica content, has been shown to help reduce bacteriosis, botrytis, damping off, downy and powdery mildew, moniliosis, rust, and scab (please see additional plants rich in silica near the top of this article); handle with gloves!
- oregano (Origanum vulare): A-B, A-F, A-V
- peppermint (Mentha piperita) was shown to be effective against the fungus Aspergillus niger
- radishes (Raphanus sativus): A-B, A-F, A-V
- rosemary (Rosmarinus officinalis): A-B, A-V
- sage (Salvia officinalis) has compounds like camphor and thujone to fight blight (caused by bacteria or fungi) and downy mildew
- thyme (Thymus spp.) has compounds like carvacrol and thymol to help combat powdery mildew, moniliosis, rust, and scab
- wild strawberry (Fragaria vesca) has compounds that have displayed notable activity against fungal strains
- wormwood (Artemisia spp., such as absinthium), contain ethyl acetate and ethanol in flowers, leaves, stems & roots that display effectiveness against fungi like rusts, plus nematodes
- yarrow: A-B
*1 The mineral silica can lend strength and vigor to plants, given its ability to improve both the cell wall structure of plants as well as plant metabolism, helping increase plant resilience to both biotic (animals, bacteria, fungi) as well as abiotic (drought, heat, salt) stresses.
Regarding biotic stress, researchers report that silica can 1) change the composition of the plant in a way that it becomes less enticing to bacteria and fungi, and 2) the molecular structure of a plant, acting as a physical barrier to infiltration and reducing plant susceptibility to enzymatic degradation by fungal pathogens. As a result, damage by fungi is lessened.
Researchers also report that plants can better withstand extreme heat and drought under silica application.
One method of benefitting plants is by ensuring natural silica is present in the soil. While adding diatomaceous Earth to the soil is an option, care is warranted to not inhale the dust, and to not create excessive concentration in the soil.
My favorite method is by adding silica-accumulating plants to the soil and to compost, allowing area plants to uptake the silica they need. A second-favorite option is through a silica-infused, water-based solution, to be delivered throughout the life cycle of the plant.
*2 Horsetail notes: Horsetail (Equisetum arvense) is native to the temperate northern hemisphere and throughout the arctic, and produces an aggressive network of rhizomes that can penetrate soils to a depth of 6 feet, rendering it tenacious once established. If you choose to plant her, designating (and dedicating!) an area away from horses is likely needed.
Alternatively, dried, non-reproductive (sterile) aerial parts of horsetail can be added to compost, or used to make water-based teas for irrigation or as a natural fungicide for powdery mildew and blight.
If you have space, horsetail is an incredible plant, especially helpful in reviving areas, as it resonates strength and resilience, bringing in divine energy to bolster all who receive and accept it, helping to affirm one’s purpose (regardless of species).
Sources:
Journal of Medical Plant Studies, 2005-2025
USDA Plant Database