Signs of Overfertilizing Carrots

Foliage

• While healthy, leafy tops are signs of growth, too much green foliage is often the first sign of soil nutrient imbalance. Too much nitrogen leads to excess foliage development, often to the detriment of root growth. Roots are perhaps the most eaten part of carrot plants. Avoid overfertilizing your carrot plants so they don't get too much nitrogen. Separate your fertilizer applications. One application can be done before planting and the second application can be done halfway through the growing season.

Insects and Diseases

• Too much foliage in carrots that were overfertilized can lead to heavier infestations of insects as well as make the carrots more susceptible to diseases. Aphids, leafhoppers and whiteflies are common pests for overfertilized carrots because the abundant plant tops are prime plant-sucking locations. Instances of root rot, blight and powdery mildew also can be signs of high nitrogen levels in the soil because leafy tops often lead to excess moisture, creating damp, humid conditions where those diseases thrive.

Root Formation

• Excess nitrogen in the soil can cause carrot roots to develop poorly or, in some cases, not at all, which means no carrot harvest. Because so much of the plants' energy goes toward developing leafy tops, little energy is given toward healthy root, and thus carrot, development. In addition to separating your fertilizer applications into two stages, use a fertilizer that is rich in potassium and low in nitrogen to avoid overfertilizing. An example is a 5-10-10 blend fertilizer, with the numbers representing nitrogen, phosphorus and potassium, respectively.

Root Problems

• Overfertilized carrot plants can lead to forked or "hairy” roots. Forked roots are common if carrots are overfertilized immediately after planting. In order to avoid forked roots, do not add manure to the soil immediately before planting, according to a University of Rhode Island Landscape Horticulture Program website article. Hairy roots are small, hairlike rootlets that result from too much nitrogen in the fertilizer. Avoid that situation by adding composted manure the season before planting to ensure a nutrient-rich soil that is not too heavy in nitrogen.