Rhubarb is grown for its fleshy stalk. The leaves are poisonous and should be removed when the stalk is harvested. This cool season crop has both pest and disease problems. Consider companion planting to prevent problems and make the rhubarb grow better. Here are the best plants to use and the few you should not use as companion plants.
Why Do Rhubarb Need Companion Plants?
Here are the ways companion plants help Rhubarb.
Some plants, such as catnip, deter pests by their odor. They can also deter mice and other rodents, as well as rabbits. Planting these companion plants in the same row, in a circle around the plant, or in the next row from rhubarb can protect it from these pests.
Flowering plants that are planted near rhubarb for other reasons also bring pollinators to the rhubarb plant. Flowers like chives, catnip, and others attract bees and butterflies to the area. They also visit the rhubarb plant while they are there.
Bring Pest Predators
Other plants, such as dill, attract pest predators which will spread to nearby plants. Rhubarb benefits from having these plants in the same row or nearby so they eat any pests on the rhubarb plant.
Plants such as beans increase the nutrients available to the rhubarb plant. They fix nitrogen from the air that goes into the soil where rhubarb can absorb it. Other plants, such as beets, have deep taproots that bring nutrients and water up into the root zone where rhubarb roots can absorb them.
Some plants, such as strawberries, act as a living mulch that suppresses weeds. They also keep the soil cooler and moist, benefiting rhubarb. Plant these plants in a circle as close as six inches from rhubarb to use as mulch.
Breaking Up Soil
Plants with long tap roots such as beets break up heavy soil. They make cracks in the soil for water and air to enter. In addition, rhubarb roots can grow into these spaces, allowing them to grow bigger and deeper than they could otherwise.
Benefit from Rhubarb
Rhubarb benefits some plants by repelling pests so they can grow unmolested. Its odor repels aphids and other insects.
You can read more about companion plants in general in my article, “Companion Planting – Everything You Need to Know.”
Top 10 Best Companion Plants for Rhubarb
Here are the top ten companion plants for Rhubarb and what they do to help grow good crops of rhubarb for you to enjoy.
Beets help rhubarb in several ways. Beets have long roots, down to 36-48 inches deep. They draw up nutrients and water. Beets excrete the excess nutrients and water into the soil, where rhubarb can reach it. Beets also break up the soil for rhubarb so rhubarb’s roots can grow better. In addition, beets keep rhubarb from getting too woody or losing too much flavor prematurely. Rhubarb helps beets by shading them later in the season when it gets hot, keeping them from bolting prematurely. Plant beets in the spaces between the rows containing rhubarb for the best results.
Catnip is an aromatic plant whose smell repels mice and other rodents. It also repels aphids, beetles, cabbage worms, and other pests. In addition, catnip attracts pollinators for rhubarb. Catnip can go in a circle around the rhubarb or in the adjacent row. Catnip may attract cats that roll in it and damage nearby plants. You can place chicken wire over the catnip to stop the cats from rolling in it. Make a dome over the catnip with the chicken wire and anchor the ends in the dirt or under heavy bricks.
Dili is another aromatic plant whose smell deters aphids. It also serves to attract pest predators, which spread to the rhubarb to eat. Dill’s long taproot draws nutrients and water to the surface. It draws up more than it can use so it excretes the excess into the soil, where rhubarb can use it. Dill also breaks up heavy soil, allowing rhubarb’s roots to spread. Finally, dill attracts pollinators. Plant dill within two to three feet of the rhubarb to give the rhubarb the most benefit.
Alliums include garlic, onions, chives, and leeks. All of the alliums have a strong odor. This odor repels insect pests from rhubarb. Alliums specifically repel ants, which are often a problem for rhubarb, leaf beetles, aphids, and whiteflies. They even deter rabbits and possibly slugs from eating rhubarb. Chives attract pollinators with their flowers. Alliums benefit from the light shade provided by the rhubarb. Plant the alliums in the next row or in a circle around the rhubarb for the best results.
Marigolds have a strong odor that repels insect pests. They also help deter root-knot nematodes when tilled into the soil and allowed to rot. Marigolds attract predatory insects that spread to the rhubarb and eat pests. They also attract pollinating insects such as bees and butterflies. Marigolds help rhubarb grow better because of the chemicals marigolds excrete into the soil. Plant the marigolds around the rhubarb for the best results.
Sage attracts predatory insects that spread to the rhubarb plants and eat pests on them. The purple flowers attract pollinators. Sage breaks up heavy soil so the rhubarb roots can spread down further. Sage does get quite large, so make sure you plant it far enough that it will not overshadow rhubarb and keep the rhubarb from getting enough sun. Space the sage so the mature plant will be within two to three feet of the rhubarb but will not cast a shadow on it.
Strawberries make an excellent living mulch for rhubarb, keeping the soil cool, moist, and free of weeds. Their deep taproots break up the soil so rhubarb roots can grow deeper. In return, strawberries benefit from the shade rhubarb provides. Plant strawberries within about six inches of the rhubarb plant to take advantage of their mulch function.
Beans fix nitrogen out of the air and deposit some of it into the soil for rhubarb to use to grow. In return, rhubarb protects beans from aphids. Use bush beans instead of pole beans to make sure the beans do not shade out the rhubarb plants. Plant the beans in the next row or in a circle around the rhubarb but about a foot away from it.
Peppermint’s strong odor repels aphids and other insect pests that attack rhubarb. It also attracts pollinators. Peppermint, like all mints, can be invasive so you may want to plant it in a container and set the container next to the rhubarb. Otherwise, it spreads and chokes out less vigorous plants, and may choke out the rhubarb by vigorously extracting nutrients from the soil.
Broccoli, Cabbage, and Related Plants
The Brassica family includes cabbage, broccoli, cauliflower, kale, and other similar plants. Rhubarb deters whiteflies from attacking plants in the Brassica family by excreting an odor the whiteflies do not like. Plant the Brassicas in the next row for the best results.
Top 5 Worst Companion Plants for Rhubarb
These plants do not go well with rhubarb and should be separated.
Rhubarb is related to sunflowers and thistles. They all suffer from curculios, a weevil that bores into cylindrical stalks to lay its eggs. Don’t plant rhubarb near sunflowers and thistles because any curculios those plants draw will spread to the rhubarb. Separate them by at least six feet and plant something between them that is aromatic, so the curculios won’t want to cross that crop to reach the rhubarb.
Cucumbers, Melons, and Pumpkins
Cucumbers, melons, and pumpkins are vigorous vining plants. They can overrun rhubarb and rob it of sunlight and nutrients. It is best to plant these plants at least ten to twelve feet from rhubarb to avoid problems.
Dock attracts insects that eat rhubarb. Curculios and other insects live on the dock and will spread to rhubarb. Again, plant the dock at least six feet from the rhubarb and plant something aromatic in between the two.
Black walnut produces a toxin that kills other plants. It will keep rhubarb from growing and will kill transplants and seeds. This toxin can persist for many years after the black walnut is removed. Do not try to plant rhubarb anywhere black walnut has been planted in the best decade. Make sure any rhubarb plantings are outside the dripline of the tree when it was alive.
Fennel, like black walnut, produces a toxin it excretes into the soil that kills all other plants. Fennel should be isolated in a corner of the garden away from other plants, including rhubarb.
In conclusion, rhubarbs grow well with beets, dill, catnip, alliums, marigolds, sage, beans, strawberries, broccoli and related plants, and peppermint. Rhubarb should not be planted near sunflowers, thistles, cucumbers, melons, pumpkins, dock, black walnuts, and fennel.