Companion planting is a gardening technique where different species are grown close together to provide mutual benefits, such as enhanced growth, natural pest control, or improved flavor. Garlic (Allium sativum) is a powerful and low-maintenance plant in this practice due to its strong sulfurous compounds and compact, shallow root system. These natural defenses make it an effective living barrier for many garden pests. This guide explores the best and worst companions to maximize the health of your garlic harvest and garden productivity.
Plants That Enhance Garlic Growth and Health
Garlic benefits from companions that improve its growing environment by boosting soil quality or deterring root-level pests. Planting chamomile nearby is believed to increase the production of essential oils in the garlic, resulting in a more potent flavor profile at harvest time.
Flowers like marigolds offer defense against soil-borne threats. French marigold varieties release a chemical called alpha-terthienyl that is toxic to root-knot nematodes, microscopic worms that feed on garlic roots. Their strong scent also helps repel pests like onion thrips.
Low-growing leafy greens, such as spinach and loose-leaf lettuce, serve as a living mulch. These plants have shallow root systems that do not compete with the deeper garlic roots for nutrients or water. Their foliage shades the soil, which suppresses weeds and conserves soil moisture. Other beneficial herbs like yarrow and summer savory improve the overall vigor of the garlic plant, with savory specifically deterring the onion fly.
Crops That Benefit From Garlic’s Presence
Garlic’s primary value as a companion plant is its broad-spectrum pest-repelling action. The strong sulfur compounds, including allicin, are released through the leaves and roots, confusing pests that rely on scent to locate host plants. Planting garlic near roses effectively deters aphids and the sulfur absorbed by the rose can help prevent fungal issues like black spot.
Garlic acts as a shield for plants frequently targeted by insects. Interplanting garlic with brassicas, such as cabbage, broccoli, and kale, repels pests like cabbage loopers, cabbage worms, and diamondback moths. Planting garlic near tomatoes can reduce populations of spider mites and aphids, and its natural antifungal properties help suppress certain fungal diseases.
Root vegetables like carrots also benefit. The pungent aroma masks the distinct smell of the carrots, making it difficult for the carrot rust fly to locate the crop to lay its eggs. Placing garlic around the drip line of fruit trees offers protection against borers and aphids, and the sulfur compounds help prevent fungal issues such as apple scab.
Companions to Strictly Avoid
Some plants should never be placed near garlic due to direct competition or chemical incompatibility that can lead to stunted growth and reduced yields. The most important plants to separate from garlic are legumes, including beans and peas. Garlic is allelopathic to legumes, meaning its sulfur compounds interfere with the specialized bacteria on the legume roots responsible for fixing nitrogen in the soil. This interference stunts the growth of the legumes and can result in smaller garlic bulbs.
Asparagus is another crop to keep at a safe distance because it is a perennial that requires significant space and nutrients. Garlic and asparagus compete aggressively for the same resources, inhibiting the development of both the garlic bulb and the asparagus spears.
Many herbs like sage and parsley are heavy feeders and compete directly with garlic for phosphorus and other nutrients needed for bulb development. Finally, avoid planting garlic near other alliums, such as onions and leeks, because they are susceptible to the same pests, like the onion maggot, which increases the risk of a localized infestation.