Rhubarb is a hardy perennial, botanically a vegetable often treated as a fruit, that can remain productive in the garden for decades. Because it occupies the same spot year after year, the surrounding soil ecosystem is important for its long-term health. Strategic companion planting involves choosing neighbors that either enhance the rhubarb’s environment or, at minimum, do not interfere with its substantial nutritional needs and deep root system.
Plants That Must Be Avoided
A primary group of plants to avoid includes heavy feeders, which compete directly with rhubarb for the high levels of nitrogen and phosphorus it requires to produce thick, red stalks. Vegetables such as corn, tomatoes, and potatoes all demand significant soil nutrients and should be planted a considerable distance away from the rhubarb patch. This competition for resources can stunt the growth of the perennial crop, leading to thin and less vigorous harvests.
Another category of plants to exclude are the sprawling vining crops like pumpkins, melons, and cucumbers. These gourds not only have high nutritional demands but also spread aggressively across the ground. Their large leaves can quickly overtake the rhubarb crown, blocking the sunlight necessary for robust photosynthesis and proper growth.
Weeds and other plants that harbor specific pests must be swiftly removed. The common weed known as dock, for example, is a host for the rhubarb curculio beetle, an insect that bores into the plant’s stalks and ruins the harvest. Sunflowers can also attract this same pest, making them poor planting partners despite their height.
Finally, any plant that secretes toxic compounds into the soil must be kept away. Black walnut trees produce a chemical called juglone, a natural herbicide that severely inhibits the growth of many sensitive garden plants, including rhubarb. Planting rhubarb within the black walnut’s root zone will likely result in plant failure.
Understanding Negative Effects
Certain pairings increase the risk of pest and disease transmission between plants. Dockweed, a relative of rhubarb, is infamous for attracting the rhubarb curculio, a snout beetle whose larvae damage the stems, causing a characteristic gummy sap to appear on the stalks. Removing dock helps break the pest’s life cycle and protects the perennial rhubarb crown.
Physical competition is another detrimental effect, especially from tall or sprawling crops. Taller plants, such as corn, cast significant shade over the large leaves, which need ample sunlight to produce energy. Vining plants like pumpkins and squash create a dense canopy that smothers the rhubarb, limiting air circulation and raising the risk of fungal diseases in the humid, shaded environment.
Beneficial Companion Plants
The best companions are those that actively improve the soil or deter pests without competing for resources, or they are shallow-rooted plants that utilize the shade provided by rhubarb’s large leaves. Members of the allium family, such as garlic, onions, and chives, are excellent choices because their strong aromas confuse and repel common rhubarb pests like leaf beetles and weevils. These aromatic plants also have shallow root systems that do not interfere with the rhubarb’s deep, extensive roots.
Flowering herbs and annuals provide additional ecological benefits:
- Nasturtiums and marigolds act as trap crops, drawing aphids away from the rhubarb, and their vibrant blooms attract beneficial insects.
- Herbs like sage and dill have deep taproots that help break up and aerate the soil, which is beneficial for compacted ground.
- Low-growing, non-competitive plants such as strawberries and creeping thyme act as a living mulch, suppressing weeds and conserving soil moisture.
- Many brassicas, including kale and broccoli, thrive in the partial shade provided by the rhubarb’s large leaves and do not compete with the deeper root zone.