Rue (Ruta graveolens) is a perennial herb historically cultivated for its ornamental blue-green foliage, strong musky aroma, and use in traditional medicine. The plant, sometimes known as the “herb of grace,” possesses a polarizing nature within the garden ecosystem. Its potent biochemical composition makes it a powerful ally against certain garden pests, yet it can be a detrimental neighbor to other cultivated species. Understanding these complex chemical interactions is the foundation for successfully incorporating this herb into any garden design.
Plants That Thrive Near Rue
The strong, characteristic scent of Rue is responsible for its positive influence on nearby plants, acting as a natural deterrent to several common garden nuisances. This herb is effective at repelling damaging insects, making it a valuable companion for susceptible plants. Roses, for instance, benefit greatly from Rue’s presence, which helps to keep away destructive pests like Japanese beetles and aphids.
Raspberries are another crop that benefits from this protective effect, as Rue’s compounds help deter beetles and aphids from damaging the canes and fruit. Gardeners strategically plant Rue near onions to ward off the onion fly larvae. Other plants, such as figs and alpine strawberries, also experience reduced pest pressure, including fruit flies and slugs, when grown in the vicinity of Rue.
Plants That Are Harmed By Rue
Rue’s chemical strength can be antagonistic to several popular herbs and vegetables. The herb releases phytotoxins that inhibit the growth and development of specific neighboring species. This often results in stunted development or altered, unpalatable flavors in the affected produce.
Gardeners should never place Rue near culinary favorites like basil, which is highly sensitive to the herb’s inhibitory compounds. Common garden staples such as cabbage and cucumbers exhibit poor growth when planted too close to Rue. Other perennial herbs, including common sage and mint, are also negatively affected by the herb’s proximity and should be isolated.
The Chemical Basis of Rue’s Influence
The herb’s powerful interactions are rooted in allelopathy, a process where a plant releases biochemicals (allelochemicals) that affect the growth of other organisms. In Rue, this function is driven by several classes of secondary metabolites that serve as the plant’s defense system. The insect-repelling quality is attributed to methyl ketones, particularly 2-undecanone and 2-nonaone, which act as fumigants against pests like spider mites.
Rue also contains alkaloids and furocoumarins, potent compounds responsible for both deterring pests and inhibiting the growth of sensitive plants. These allelochemicals enter the environment through root exudates, leaf litter, or volatile emissions, directly impacting the germination, survival, and growth of nearby competitors. This process reduces competition for resources like water and nutrients, which explains the stunted growth observed in its sensitive neighbors.
Strategic Placement and Safety
Integrating Rue into the garden requires strategic isolation to harness its benefits while mitigating risks to both plants and people. Due to its allelopathic nature, the herb should be placed a significant distance away from sensitive crops like basil and cabbage to prevent growth suppression. Planting Rue in a dedicated herb border or container garden, away from the main vegetable beds, ensures its protective qualities can be utilized without harming vulnerable neighbors.
The herb contains phototoxic compounds called furocoumarins (psoralens) that pose a risk to human health upon contact. When these chemicals touch the skin and are exposed to ultraviolet light, they can cause phyto-photodermatitis, resulting in redness, burning, and blistering. Gardeners should always wear long sleeves and gloves when handling or pruning Rue, especially on sunny days, and wash accidental skin contact immediately with soap and water.