Tiny arachnids that are known for causing significant damage to hundreds of types of plants, spider mites are some of the worst pests to have in an ornamental garden. They create colonies close to the veins and along the undersides of fleshy foliage. To feed, these mites often puncture holes or damage the soft tissues of plants in order to access their nutritious sap. For protection from potential predators, they create unsightly webs.
A considerably-sized colony of spider mites can wreak enough damage to cause leaf discoloration, leaf scorching, and leaf loss. Over time, these issues may prevent victimized plants from efficiently producing their own food, leading to their eventual death. Spider mite colonies may also attract more pests, compounding the ill effects of multiple infestations. Fortunately, there are several methods of eliminating them and minimizing their spread.
In the wild, spider mites are naturally controlled and eliminated by many types of predatory and beneficial insects (e.g. ladybugs, lacewings). Some specialized plants, particularly those that produce acaricidal compounds, are also able to help keep mite colonies at bay, preventing them from infesting more vulnerable species. While these companion plants cannot fully take the place of systemic pesticides, they are perfect as environment-friendly forms of pest control.
1) European dill (Anethum graveolens)
An aromatic herb with a rich history, dill was cultivated as far back as ancient times. It is lauded for the strong flavors and potent oils of its threadlike leaves. Simply rubbing the leaves or breaking off a few leaflets releases the plant’s distinct scent. With its complex cocktail of essential oils, dill is packed with antimicrobial phytochemicals. Some of these are naturally acaricidal, which means they are toxic to spider mites.
To maximize the effectiveness of dill as a pest-repellent plant, it should be cultivated alongside companion vegetables and herbs like tomatoes, cabbage, cucumbers, broccoli, and lettuce. Dill clusters placed around plots of these plants, or in containers around their stands, should effectively keep spider mites away. In the case of established colonies of these arachnids, however, a targeted organic pesticide should be used.
Dill grows best in regions with warm summers and lengthy daylight hours. Dill seeds that are germinated in a rich, well-draining substrate quickly grow into productive shoots. If you’d like to attract beneficial insects that are likely to feed on spider mites, the shoots should be permitted to come into bloom before being pruned back. Note, however, that the production of dill flowers may compromise the growth of nearby plants.
2) Chinese parsley (Coriandrum sativum)
Chinese parsley is also commonly known as cilantro, coriander, and dhania. It is an annual herb with a wealth of culinary uses. Its leaves and roots emit an intense smell and produce an even more notable and distinct flavor. Like many other plants with citrus-like scents and flavors, its botanical uses far exceed those in the kitchen. It is a fantastic species to grow in an herb and vegetable garden as a natural pest deterrent.
The essential oils of various parts of Chinese parsley are rich in active insecticidal compounds. In their extracted forms, they have been shown as an effective acaricide against several troublesome garden pests. The oil from the fruit, which is predominantly composed of linalool, is especially potent. Many insects and foragers are thus likely to avoid dense stands of this species. Occasional pruning should enhance its repellent fragrance.
Hardy to USDA zones 2 – 11, Chinese parsley is a versatile plant that can be grown either indoors or outdoors. Its highest productivity rates are usually associated with full sun exposure and a well-draining substrate. If you find that it grows well in your garden but does not seem to repel any pests, you might want to try incorporating its leaves into a homemade pest-repellent spray.
3) Onion (Allium cepa)
Members of the Allium genus are generally some of the best pest-repellent plants because of their intense scents. Both the specialized root systems and the exposed foliage emit their pungent fragrance when they are mechanically damaged. Intact plants may likewise repel pests, but their effects may not be strong enough to prevent serious infestations from occurring. Nonetheless, small stands of these plants should collectively work to control pest populations.
The humble onion, arguably one of the most popular root crops due to its culinary importance, contains many pesticidal phytochemicals. Its extracted oils were proven to be an effective acaricide on some ticks, so they are likely to be toxic to spider mites as well. Onion extract is also effective as a pesticidal agent when applied directly to affected plants.
Some plants that can benefit from being planted next to onions include carrots, spinach, parsnip, beets, strawberries, lettuce, and cucumbers. Many of these have their own insecticidal phytochemicals, so they can work in a synergized manner to repel a diversity of pests. Avoid growing onions next to other Allium species as their concentrated growth can draw maggots that specifically target the genus.
4) Chrysanthemums (Chrysanthemum spp.)
Known for their undeniably eye-catching blooms, chrysanthemums are some of the most attractive ornamental plants to grow in a home garden. With their impressively-sized flower heads, they are able to attract many beneficial insects, some of which naturally prey on spider mites and other small plant pests. With countless varieties to choose from, you can fill a single garden with these useful perennials.
The principal insecticidal component of chrysanthemums (pyrethrin) is found in their flowerheads, so a truly pest-repellent garden should have other plants that produce repellent compounds outside of the bloom period. The flowerheads can, however, be harvested and used to keep all manner of pests away even during cool months. Drying and pulverizing the flower heads preserves their pyrethrin content. The powdered material can then be dusted onto infested plants.
While powdered pyrethrin does repel spider mites, it has been associated with resurgences of this pest. Its application causes colonies to disperse, distributing fecund individuals onto nearby plants where they may eventually cause infestations. It may be best to use it accompanied by other methods of secondary treatment as its sole application may backfire.
5) Garden rhubarb (Rheum rhabarbarum)
Garden rhubarb is a lovely species for adding color and texture to an herb garden. A vegetable that is chiefly cultivated for its edible petioles, its leaves, in comparison, are inedible because they contain irritants and toxic phytochemicals. Oxalic acid, a major component of the leaves, functions as an effective insecticide and grazer deterrent.
The effects of garden rhubarb extend to spider mites as these arachnids are unlikely to ever produce colonies on the leaves. They cannot utilize the poisonous sap as a source of necessary nutrients for their growth and expansion. You can thus cultivate rhubarb around plants with highly susceptible and edible foliage.
As an added measure of protection, plants that are frequently infested with spider mites can be sprayed with a rhubarb-based insecticide. To create this at home, collect a few crisp rhubarb leaves and place them in a small pot of boiling water. Allow the solution to cool and then transfer the liquid into a spray bottle. Once a dash of dishwashing soap is added, the spray should be ready to use on affected leaves.
6) Chives (Allium schoenoprasum)
Chives is one of the best companion plants for tomatoes, which are particularly sensitive to red spider mites (Tetranychus urticae). This perennial herb is chiefly grown for its flavorful leaves. Often used as a garnish in Eurasian dishes, the leaves contain a wealth of compounds with the potential as natural acaricides. Moreover, their anti-inflammatory and antifungal properties have made them pharmacologically valuable.
Widely cultivated as far back as the Middle Ages, chives are one of the most straightforward herbs to germinate and harvest. It can be grown indoors – right in the kitchen where its sprigs can be cut and dropped into the pan, or next to tropical houseplants that are more susceptible to spider mites. As the leaves demand to be cut back for the plant to produce new batches of fresh foliage, the repellent sap can frequently be released.
Horticulturists and farmers throughout this herb’s native range have historically used it as a natural pest repellent. Due to its manageable size and limited spread, it can be planted in between the rocks bordering a flower or vegetable garden. Its extracted oils can likewise be used as a natural insecticide.
7) Shasta daisy (Leucanthemum x superbum)
Developed by Luther Burbank, a horticulturist who specialized in various daisies in the 1890s, the Shasta daisy is a valuable ornamental herb. It is a complex hybrid between three Leucanthemum and Nipponanthemum species coming from three different continents! Named after the snowy Mount Shasta of California, it is characterized by the best features of its parent plants.
The Shasta daisy’s delicate white petals surround a large yellow disc of tiny florets. With a bloom configuration similar to that of other daisies, this hybrid attracts a wealth of beneficial insects (e.g. ladybugs, pirate bugs, predatory mites). Its appeal to these natural pest predators is predominantly what makes it an effective pest repellent. Its stands should be strategically placed so that their benefits may be distributed throughout the garden.
The use of the Shasta daisy as a natural pest repellent highlights the importance of maintaining a biodiverse collection of plants to minimize the occurrence of pest infestations. In the absence of insecticidal compounds, ornamental plants can be just as useful at keeping pests at bay by enhancing the balanced presence of their pollinators. Note, however, that while this hybrid does attract insects, it seldom attracts pollinating bees because of its absence in the wild.
8) Rosemary (Salvia rosmarinus)
A member of the sage family (Lamiaceae) of strongly-scented herbs, rosemary is another culinary staple with many benefits in the ornamental garden. Frequently cultivated as a shrub in loamy to sandy substrates, its increasingly woody shoots can grow as tall as 5 feet (1.5 meters). In areas with warm climates, its blooms can appear throughout the year, attracting many pollinators and beneficial insects.
This hardy herb is unappealing to many pests and grazers due to the toughness of its leathery foliage and due to its bitter taste. This taste signifies the potent nature of its rich essential oil, which has scientifically been tested against a common pest – the two-spotted spider mite (Tetranychus urticae). The pure extract, along with other products that make use of rosemary oil as a base ingredient, has shown potential as an effective acaricide.
As this herb is fairly drought-tolerant, it is a better option for areas of the garden that receive little to no moisture throughout most of the year. It would also be an ideal choice as a companion plant for desert herbs and succulents. That being said, however, it will require a regular watering regimen to achieve desired growth rates.
9) Garlic (Allium sativum)
Touted as one of the most important crops in the culinary world, garlic is a fantastic source of flavor. It is a fundamental ingredient in many cuisines, able to considerably alter the taste of practically any dish. Its wondrous properties are largely due to the high concentration of sulfur-containing compounds in its edible cloves. The strong scent and flavor of these compounds are released when the bulb is mechanically damaged or cooked.
While the pungent smell and flavor of garlic may appeal to us humans, they are absolutely detested by many insects and grazers. For this reason, garlic is included in many homemade or organically-produced pest-repellent sprays for use in the garden. Its extract is the perfect, eco-friendly weapon against spider mites and the like!
Garlic is just one of many plants with compounds that are effective against red spider mites and two-spotted spider mites, both of which frequently attack vegetables and herbs that are mass-cultivated in plantations. Unfortunately, an intact and buried garlic bulb isn’t the best insecticide as its compounds need to be extracted and released to be effective. Nonetheless, it is still generally avoided by troublesome insects.
10) Peppermint (Mentha x piperita)
A natural hybrid between spearmint (M. spicata) and watermint (M. aquatica), peppermint is one of the most popular types of mint plants because of its attractive garden cultivars. Many of these are commercially grown and used to produce food-grade extracts. The extracts contain compounds with the potential for use as natural pesticides.
Pulegone and menthone, dominant phytochemicals in the essential oils of many mint species, are particularly effective at repelling pest insects. Menthol, a terpenoid in peppermint, has been shown to be promising as an acaricidal agent against the two-spotted spider mite. The intact leaves of peppermint may aid in repelling spider mites on sensitive species that are situated directly adjacent to its stands. However, the scent released by exposed sap (from wounded tissues) should be even more effective.
Apart from producing chemicals that repel many destructive pests, peppermint is also great at attracting beneficial insects. Its light-purple blooms, which appear in summer, attract honeybees and the like. Unfortunately, as it is a hybrid, it produces just a few sterile seeds. Its stands chiefly spread by vegetative means, and they do not self-seed. To maximize their use as a natural repellent, harvest the leaves and make a peppermint-based pest spray.
