Daucus carota Full Sun Soil pH: 5.5 - 7.5
Companion Planting is the placement of various crops in close physical proximity to one another so as to symbiotically compliment each other. Naturally, it also involves separating plants whose development is antagonistic to each other.
Dill - It is believed , but not proven, that young dill actually enhances plant vigor of its neighbors and mature Dill stunts the growth of some plants including carrots. Dill and carrot are actually related plants. If dill bolts or is allowed to flower, it can cross pollinate with carrots and vice versa.
Coriander aka Cilantro, like dill produces root excretions that are harmful to carrots.
Onions, garlic and other onion-family plants are great companion plants for carrots because they repel or deter insect pests that favor Carrots. Leeks planted with carrots emits a scent that acts as a repellent of carrot pests, in particular the carrot rust-fly. Onions also mask the odor of carrots, confusing pests and keeping them uninterested. onions impede the growth of beans, peas and legumes. Beans and related crops are compatible with carrots - but should not be mixed with carrots and onions.
Chives, another onion related plant is believed to improve the tastes of carrots. There is no scientific evidence that I am aware of to prove this other than my own personal experience. I've inter-planted chives and carrots many seasons and I do believe they improve the quality of the carrot.
Peas grow well with Carrots due to the nitrogen fixing properties of the peas which theoretically help to satiate the nutrient requirements of carrots. Carrots however are not heavy feeders , they don't require excessive nitrogen so although the beans and legumes planted with carrots is not a bad thing, it doesn't do a whole heck of a lot for the carrots.
The Carrots do act as a deterrent for some pests that hinder Peas and some related crops. Bush Beans - ditto ... Snap Beans - ditto ... Green Beans - ditto ...
Carrots and Lettuce fare well together. Carrot roots grow relatively deep in the soil while lettuce roots grow relatively shallow. The carrots will be drawing moisture and nutrients from a different level than the shallow rooted lettuce. The lettuce serves a semi- living mulch and helps retain soil moisture. Planting them together benefits both. Alternating rows of lettuce and carrots works best.
"Lettuce and carrots are examples of examples of vegetables that can be combined due to biological, nutritional, economic and social reasons, representing an alternative for food production and income." Effect of intercropping on the population density of pests in some vegetables
Inter-planting carrots and Tomatoes requires good timing. Carrots mature more rapidly than tomatoes so your first harvest of Carrots should be when the Tomatoes are still seedlings.
Mature carrots and mature tomatoes should not share the same soil as they compete for the same nutrients at the same time. A second planting of carrots is also possible in some zones, calculating their maturity to be after the bulk of the Tomatoes have been harvested. Parsley, a close relative of Carrots also works fine in the same fashion.
Tomatoes secrete a natural insect deterrent called solanine which eliminates many insects that are harmful to carrots. The solanine and trace phytotoxins emitted by tomatoes can stunt the growth of carrots if planted too close.
Carrots love Tomatoes, but from a safe distance, planting the two together is a good idea - keeping them at least 1 1/2 feet apart when doing so is even a better idea.
Whether or not Tomatoes enhance the flavor of carrots is debatable, there is no proof either way other than personal observations.
Flax is grown for the oils it produces. Flax-seed oil is non toxic to humans and there is some evidence that the plants natural oils may protect carrots and other root crops.
Rosemary, which is touted as a good companion plant for carrots - really isn't - It's not a bad one either. It does little for the carrot plant and vice verse. Cuttings from rosemary might, possibly , maybe , woulda coulda shoulda act as a repellent of carrot rustfly - but that is unproven.
Sage has some repellent qualities against carrot pests.
Radish can be planted with carrots , the radish will mature very quickly and loosen the soil for the carrot seeds as they germinate. The radishes will already be harvested when the carrots are still in pampers.
Amaranth aka Pig-weed also loosens the soil, making it easier for carrot roots to grow.
Parsnips a close cousin of carrots is susceptible to the same diseases and pests as carrots. It's advisable to keep the two separated.