Carrot + Leek

Leeks release volatile sulfur compounds that interfere with carrot rust fly (Psila rosae) host-finding, making this pairing functionally similar to the better-known carrot-onion combination. Both crops are slow to mature, typically 70 to 120 days depending on variety and conditions, which simplifies bed planning since neither needs to be cleared quickly to make room for a follow-on planting.

Spacing works reasonably well in shared rows. Leeks need 6 inches between transplants; carrots are sown thickly and thinned to 2 to 3 inches. Alternating rows, with leeks toward the bed edges, reduces shading on the shorter carrot tops.

Soil compatibility is close but not identical. Carrots want deep, loose, well-drained soil low in fresh organic matter; leeks tolerate richer, slightly moister conditions. A moderately fertile, well-worked bed is a workable compromise. In compacted or clay soil, both crops struggle regardless of companion arrangement, and the pairing offers no meaningful benefit.