Kohlrabi makes a great companion crop for beets. These plants can be grown together because beet roots take nutrients from the soil at a depth greater than that reached by kohlrabi. The beet root is deeper because the edible part of the beet is underground and takes up some space. These two crops are also fertilized, weeded, planted and watered the same way. Crops that require similar management make better companions.
Other Companion Crops
Other crops have similar management requirements to and make good companion crops for beets. Onions work well with beets for the same reason that kohlrabi is a good companion. Onions have one of the shallowest root systems of all garden crops. At maturity, the onion root only mines the soil for nutrients to a depth of 1 or 1 1/2 feet. Other crops that make great companions with beets include bush beans, lettuces and cabbages.
Many crops aggressively compete for light. These should not be grown with beets. When aggressive crops are grown near beets, the beets suffer. In most cases the beet plants will not die, but the edible root at harvest time will be smaller, dryer and less nutritious. Crops that are too aggressive in their reach for sunlight to be good companions include corn, squash, watermelon, potato, tomato and sunflower.
Some plants produce chemicals that inhibit the growth of other plants. You may have noticed that not much grows below a pine tree. The pine needles give off a chemical that negatively affects the growth of most plants. Many plants have this type of chemical defense. Mustard and some flowers should not be grown with beets because they inhibit the growth of the beets.