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Carrots (Daucus carota subsp. sativus) are delicious and nutritious, but there are many other reasons to love them if you’re a gardener. Unlike many edible plants, these crunchy root vegetables will grow in partial shade and tolerate drought in your garden. Plus, they’ll thrive in USDA hardiness zones 2 through 11, which cover most of the United States. One key to optimizing your carrot crop is choosing the right fertilizer. In general, you should avoid nitrogen-rich fertilizers for carrot plants. If your carrots receive too much of this nutrient, they’ll use most of their energy for growing bushy green tops rather than long, strong roots.

Start tending to the nutrient needs of your carrots when you plant them. Though many veggie patch all-stars love loamy soil that’s packed with vitamins and minerals, carrots follow the beat of their own drum. They prefer sandy soil with lower levels of nitrogen and other nutrients. A growing medium that’s half sand and half potting soil tends to meet their needs. Generally speaking, carrots should be fertilized a few weeks after you sow their seeds. If they are growing rapidly, you might fertilize them after two weeks. Alternatively, when the weather is cold and growth is slow, you could wait until the six-week mark. If growth doesn’t accelerate or you know your soil has nutrient deficiencies, consider fertilizing your carrots again halfway through the growing season. When growing carrots in a container garden, feed them a fertilizer with little to no nitrogen every three to four weeks. 

In addition to diverting carrot plants’ energy away from root growth, which may reduce the size of the vegetables come harvest time, nitrogen-rich soil additives encourage the roots to form strange shapes as they grow. A carrot that is grumpy about nitrogen content or an obstacle in the soil — say, a stone or stick — is likely to branch off in multiple directions. Other times, it will bend or twist. Though these misshapen roots are perfectly fine to eat, they won’t win any beauty prizes. An overabundance of a balanced nitrogen-phosphorus-potassium (NPK) fertilizer can also cause this kind of carrot behavior, as can under-watered soil. To prevent forking in response to rocks and other roadblocks, try growing your carrots in toilet paper tubes.

Fresh manure, a natural fertilizer, presents additional drawbacks for carrots. Ammonium, one type of nitrogen it contains, is readily available to plants and can easily turn into ammonia. It’s prone to burning developing plant roots, making fresh manure a no-no for carrots. Plus, fresh manure can introduce E. coli to your garden and end up on crops you plan to eat. Composted manure is a different story. Adding it to your carrots’ soil is helpful, especially if you need to improve water drainage. Just be aware that it will slowly release nitrogen. To prevent nitrogen overload, tread carefully when choosing a fertilizer for later in the growing season.

Though excess nitrogen can lower the quality of your carrots, a phosphorus boost can raise it. That’s because this nutrient helps carrot plants grow hearty roots. Natural fertilizers that release nutrients slowly can feed your carrots without overwhelming them. Amending your garden soil with phosphorus-rich bone meal before sowing carrot seeds is one way to go. Topdressing your garden soil with wood ash is another option. This fireplace byproduct increases the soil’s potassium content, but it also increases the pH level, so be sure to test your soil before using it as fertilizer. 

A product such as the MySoil test kit, which measures both pH and nutrient levels, can help you determine which nutrients need boosting and what kinds of fertilizer are the best fit for your garden. Carrots prefer a pH level between 6.0 and 7.0, so you’d want your starting point to be lower than this if you plan to use wood ash as a phosphorus supplement. If your carrots would benefit from more of several nutrients, try compost tea. Simply soak 1.5 cups of compost in a gallon of water for a week and then water your carrots with the liquid.

Synthetic fertilizer is another way to give carrots phosphorus and other sources of nutrition. A liquid formulation is ideal because you don’t have to work it into the soil, which could disturb the roots of your carrot plants. Farmer’s Secret super-concentrated 8-16-8 plant booster has lots of the phosphorus carrots need and a relatively small amount of nitrogen. For optimal results and maximum safety, follow the instructions on the fertilizer package.