Asparagus is a unique, long-lived perennial crop that can produce spears for 15 years or more once established. Because of this extensive lifespan, the planting location is permanent, making the initial choice of neighboring plants crucial. Companion planting involves growing different crops together for mutual benefit. Selecting the correct companions can improve soil health, deter pests, and maximize the overall productivity of the asparagus patch.
Plants That Help Asparagus Thrive
Many beneficial plants can be interplanted with asparagus to offer support, primarily through pest repulsion and minimizing root competition. The most effective companion is the tomato plant, which provides an important natural defense. Tomato plants contain the compound solanine, known to repel the asparagus beetle, a common pest that damages spears and foliage. In a mutually beneficial exchange, asparagus roots are thought to exude compounds that help deter root-knot nematodes, which attack the tomato’s root system.
Aromatic herbs and flowers also serve as excellent companions by deterring pests and attracting beneficial insects. Basil and parsley are particularly effective, as their strong scents can help repel the asparagus beetle while attracting pollinators and beneficial predators like ladybugs and lacewings. Dill and cilantro, with their shallow root systems, also repel spider mites and aphids, making them non-competitive allies.
Marigolds, especially French marigolds, are highly valued for their ability to suppress soil nematodes through a chemical released from their roots. Nasturtiums can be used as a “trap crop,” drawing aphids away from the asparagus ferns. These flowers and herbs thrive because their shallow root systems do not compete with the deep-growing asparagus crowns for water and nutrients. Low-growing, short-season vegetables like lettuce, spinach, and beets are also suitable because they are harvested early.
Crops That Compete or Cause Harm
Gardeners should avoid planting crops that actively compete with asparagus for deep-soil resources or share common diseases and pests. The entire Allium family, which includes onions, garlic, leeks, and chives, should be kept at a distance. These plants are thought to stunt asparagus growth by heavily competing for nutrients and may also introduce Fusarium species, which can cause crown and root rot in asparagus.
Deep-rooted vegetables like potatoes and carrots are also poor companions because their extensive root systems directly compete with the deep asparagus crowns. Potatoes, in particular, can compete for moisture and nutrients, while the physical act of harvesting deep-growing carrots can easily damage the sensitive, permanent asparagus rhizomes. Vigorous, large-growing brassicas should also be avoided, as they can quickly deplete soil nutrients and cast excessive shade over the developing asparagus ferns.
Other plants to avoid include those that share common fungal pathogens, such as strawberries, which can transmit diseases like verticillium wilt to asparagus. Aggressive, self-seeding plants can also quickly overwhelm a newly established asparagus bed, turning into difficult-to-remove weeds that disturb the soil and compete for resources.
Essential Spacing and Layout Considerations
Because asparagus is a permanent crop, the physical layout of companion plants requires thoughtful, long-term planning. Asparagus crowns should typically be spaced 12 to 18 inches apart within the row, with rows spaced at least four to five feet apart. Companion planting should only be introduced after the asparagus crowns are established, usually after the first year, to avoid stressing young plants.
The asparagus fern, the tall, feathery growth that appears after the spring harvest, must receive full sunlight to photosynthesize and store energy for the following year’s crop. Therefore, tall companions like staked tomatoes should be positioned at the ends of rows or on the perimeter to prevent their foliage from shading the ferns. A minimum distance of 18 to 24 inches should be maintained between asparagus crowns and any large companion plant to minimize root competition.
Low-growing, shallow-rooted herbs like basil and parsley are best positioned directly between the asparagus rows where they can offer pest-repelling benefits without interfering with crown development. Using the perimeters for more aggressive or larger companions, such as nasturtiums or comfrey, allows them to provide their benefits while ensuring the main asparagus bed remains undisturbed.