Companion planting is a horticultural technique involving strategically planting different species together to create a mutually beneficial environment. Within an apple orchard, this practice acts as a form of biological management to enhance the productivity and resilience of the fruit trees. By selecting plants that perform specific functions, growers cultivate a localized ecosystem. This approach reduces the need for external inputs like synthetic fertilizers or pesticides, maximizing the natural health and yield of the apple trees.
Companion Plants for Pest Control and Pollination
Certain companion plants are selected primarily for their ability to influence the insect population within the orchard. They either repel harmful pests or attract beneficial species. These interactions are often chemically driven, relying on volatile compounds released by the foliage or roots of the companion plant.
Pest Deterrents
Many aromatic herbs function as natural pest deterrents because their strong scents confuse or repel insects that target apple trees. The pungent compounds in chives, a member of the Allium family, help prevent apple scab, a common fungal disease. Chives can also be made into a foliar tea and sprayed onto the trees as a preventative measure. Mint releases volatile compounds effective in confusing pests like aphids and ants, protecting the apple foliage. Hyssop has a bitter aroma that discourages various insects, including those that spread disease or feed directly on the fruit.
Pollinator Attractants
Successful apple production is dependent on cross-pollination, requiring insects to move pollen between compatible cultivars. Companion plants that produce abundant nectar and pollen are grown to provide forage for pollinators, such as honey bees and native wild bees, especially during the bloom period. Flowering plants like clover, dill, and chamomile serve as beneficial insect accumulators, providing a continuous food source that keeps helpful populations nearby. This presence supports both pollinators and natural predators, such as lady beetles and parasitoid wasps, which feed on apple pests like the woolly apple aphid.
Companion Plants for Soil Improvement
The physical and chemical properties of the soil directly influence the long-term health and growth rate of apple trees. Some companion plants are chosen to work primarily beneath the surface, improving soil fertility and structure. This makes water and nutrients more accessible to the apple tree’s root system.
Nutrient Cycling and Dynamic Accumulation
Plants with long, deep taproots, known as dynamic accumulators, draw minerals from subsoil layers that are typically inaccessible to the apple tree’s shallower feeder roots. Comfrey is a classic example, concentrating nutrients like nitrogen, potassium, and calcium in its leaves. When the foliage is cut and dropped onto the soil surface, the decomposing material releases these accumulated minerals back into the topsoil, acting as a slow-release mulch. Dandelions also have a significant taproot that performs this function, pulling up minerals from depth to enrich the soil when their leaves decay.
Nitrogen Fixation and Groundcover
Leguminous plants, such as clover and peas, host specialized bacteria in root nodules. These bacteria capture atmospheric nitrogen and convert it into a form plants can utilize, a process called nitrogen fixation. This naturally enriches the soil, providing a steady supply of nitrogen to the apple tree. Low-growing plants, particularly those used as living mulches, play a dual role in moisture retention and weed suppression. They cover the ground, reducing water evaporation and moderating soil temperature, while competing against opportunistic weeds.
Plants That Inhibit Apple Tree Growth
Not all plants are beneficial companions; some common species can actively harm an apple tree through chemical warfare or intense resource competition. Recognizing and avoiding these plants is an important part of orchard management, especially for young trees.
Allelopathic Inhibitors
Certain plants employ a strategy called allelopathy, releasing chemical compounds into the soil or air that inhibit the growth of nearby competitors. The black walnut tree is the most well-known allelopathic species, producing juglone, a chemical highly concentrated in its roots. Juglone can severely stunt or kill many fruit trees, including apples. Although apples are not as sensitive as nightshade plants, proximity to black walnut can still negatively affect their vigor. Other plants like goldenrod and sunflowers also exhibit allelopathic effects that suppress neighboring species.
Resource Competitors and Disease Hosts
Plants with dense root systems should be avoided because they directly compete with the apple tree for water and nutrients. Tall grasses, aggressive vines, and nutrient-hungry vegetables like corn can deplete the soil, especially around the shallow roots of newly planted apple trees, leading to stunted growth. Furthermore, some plants act as alternative hosts for diseases that can jump to the apple tree, such as plants in the juniper family, which can carry cedar-apple rust. Eliminating these disease vectors helps to break the life cycle of the pathogen and protects the apple crop.