Carrot Fertilizer [What to Use, Where to Get It, How to Use It]
One of the most frustrating things for me as a new gardener was finding a fertilizer that had the right NPK for my carrots. I knew from the University of California that it should have low nitrogen, moderate phosphorus, and high potassium levels, but trying to find something that fit that description wasn’t easy work.
Over the years I’ve done a lot of trial and error with different fertilizers and the timing and ratios. Here’s everything I’ve learned and what I think works best when it comes to fertilizing carrots.
Do Carrots Need Fertilizer
Do carrots take a lot of fertilizer? No, not really compared to other vegetables I’ve grown. Carrots require low levels of nitrogen, a moderate amount of phosphorus, and a high amount of potassium. But they only require fertilizing a couple of times during the growing season.
Reading Fertilizer Labels
If you read the label of any quality fertilizer, it should have three numbers on it. In the image here you can see it read 6-12-12.
Those numbers represent nitrogen, phosphorus, and potassium (always in that order). Or abbreviated, NPK (the letters for those elements on the periodic table).
Each number represents the percent of each element present. So in this example, there is 6 percent nitrogen, and 12 percent phosphorus and potassium in this fertilizer.
This is important because each nutrient will affect your carrots differently.
Dry Carrot Fertilizers
Fertilizers come in 3 types, liquid, foliar, and dry. I always use dry fertilizers for my carrots because the foliar and liquid ones have too much nitrogen in them which can result in lots of greenery and little carrot roots.
Dry fertilizers are made of powder or granular minerals that you side-dress your plants with on top of the soil or mix into the top few inches before sowing seeds. They dissolve slowly into the ground and roots of your carrot.
I also find that dry fertilizers are more affordable than liquid ones, they’re easier to use and store, and they’re hyperconcentrated so a little goes a long way.
Carrot Fertilizer Requirements
I think it’s worth deep-diving into the nutrients every carrot needs to reach maturity and become a sweet, fat carrot.
Nitrogen (N)
Carrots do need some nitrogen. Nitrogen is responsible for all that green foliage you see. It helps plants grow leaves and stems.
If you are planting in a raised bed with organic garden soil or you have a healthy amount of compost mixed into your soil, you can probably skip adding any nitrogen at all. There’s already enough in the soil.
I prefer the Happy Frog blend by Fox Farms here in California because it has everything your seedlings need to grow, but it’s not overfilled with a ton of nutrients.
I like this because depending on what I’m growing, it allows me to add my own soil amendments depending on the vegetable I’m growing and I’ve never had it burn my plants.
If you’re unsure about the nitrogen level of your soil, you can do a quick at-home soil test to find out.
I like to use dry, organic fertilizers. If your soil is nitrogen deficient, add blood meal to the soil.
I usually don’t add any additional nitrogen once I plant carrots. If you companion plant bush beans or practice crop rotation, you most likely won’t need any more nitrogen during the growing season.
Avoid nitrogen-heavy fertilizers during the growth stages of your carrots. Carrots are a root veggie and you want to stimulate root development, not foliage.
Phosphorus (P)
Carrots require a moderate amount of phosphorus. This helps with root development.
Again, it’s a best practice to test your soil prior to planting carrots. If you find that you are deficient in phosphorus, I prefer to mix an organic fertilizer like bone meal into the soil before sowing seeds.
I apply a phosphorus-heavy fertilizer to my carrots twice during their growth which has a P rating between 9 and 12.
Potassium (K)
Carrots require a high amount of potassium. This nutrient helps carrots develop roots but also improves the sugar content of your carrots, making them taste sweeter.
When carrots have the right amount of potassium, they will convert starch into soluble sugars, improving their flavor.
Potassium, as well as calcium, are also very important for the skin quality of your carrots.
I apply a potassium-heavy fertilizer to my carrots twice during the growing season. In the past, I’ve used a carrot fertilizer called Big A Carrots, but this year I’m experimenting with a homemade fertilizer using bone meal and langbeinite. Both of which are natural substances and not chemical-based.
Micronutrients and pH
Nitrogen, Phosphorus, and Potassium are the three primary nutrients your carrots will need to thrive, but there are other micronutrients they need as well. Those include:
Sulfur
Calcium
Zinc
Magnesium
Molybdenum
Rather than test for all these nutrients, I suggest simply testing your soil pH. I use the Luster Leaf Rapitest which includes a test for pH and all three primary nutrients N-P-K.
Soil pH should be between 5.5 and 7.5 for carrots.
If your pH is under 5.5, carrots are susceptible to phosphate, molybdenum, and calcium deficiencies.
If your pH is over 7.5, carrots are susceptible to boron, copper, iron, manganese, phosphate, and zinc deficiencies.
If you have a good pH, between 5.5 and 7.5, you don’t need to worry about adding any micronutrients to your soil before planting or during growth phases.
How to Fertilize Carrots
The key to fertilizing carrots is to always err on the side of caution. It’s always best to underfertilze. Too much fertilizer and you can end up with forked or hairy roots and even less flavorful carrots.
Pre-Planting Fertilizer
I wish I could tell you that I always test my soil before planting, but I don’t. I probably should. One thing you should do before planting is mix plenty of compost into the soil.
I have a Hot Frog Composter and in the winter it can take longer for the food to break down into compost. If you experience this, I dig trenches in my garden and add the food scraps directly under the ground at least 6 to 8 inches beneath the surface.
The worms and micro-organisms will do the rest and as your carrots grow, they’ll have the same nutrients as if you added compost to the soil.
Alternatively, you can also add a 6-6-6 fertilizer to your soil if you don’t have compost. For a 3x6 bed, add no more than 1/4 lb. For a 4x8 bed, add up to 1/2 lb.
Early Growth Fertilizer
When the carrot tops are 3 to 4 inches tall, it’s time to fertilize carrots. I use Big A Carrots which is an organic fertilizer with an NPK rating of 1-9-3.
This is also about the time when you will thin carrots for the first time. I like to thin my carrots, then mound up soil on any carrots that might be exposed to the surface, and then give the remaining carrots a side dressing of fertilizer all at the same time.
In the past, I’ve used 0-10-10 and 5-15-15 fertilizers, but I find that the Big A Carrots 1-9-3 works best.
Because it is a dry fertilizer, I always water right afterward so the nutrients start to dissolve into the soil.
Mid-Growth Fertilizer
I apply a second side-dress of Big A Carrots organic fertilizer when the carrot stems reach 6 to 8 inches in height. Whatever you use, don’t add anything with more nitrogen or you’ll end up with big foliage and split roots. Big A Carrots does have
1% nitrogen, but it hasn’t been a problem for me. I wouldn’t use anything with more than that in it.
And don’t forget to water right after side-dressing your carrots with fertilizer so the nutrients start to dissolve into the soil.
When to Fertilize Carrots
You should fertilize carrots a total of 3 times.
Fertilize by adding compost to your soil before planting carrot seeds.
Fertilize seedlings again when the carrot stems are about 4 inches tall.
And do a final fertilization when the carrot stems are 6 to 8 inches, about halfway to maturity.
Organic Carrot Fertilizers I Recommend
Here is a list of all the carrot fertilizers I’ve used and would recommend.
Bone Meal 4-12-0
I use bone meal for so many things in my garden. It’s high in phosphorus which will help with root development and has a little bit of nitrogen in it. It’s good early on before sowing seeds if you have a nitrogen and phosphorus deficiency.
Big A Carrots 1-9-3
This was a great discovery. Big A makes their fertilizer out of all-natural things like kelp, alfalfa, and langbeinite. It’s 100% organic and a great blend for your early-stage and mid-stage carrot development.
Langbeinite 0-0-22
Langbeinite is a sulfate mineral. It’s natural and a great source of potassium which makes carrots sweeter. I’m currently experimenting by blending this with bone meal for my carrot fertilizer to see if it outperforms Big A Carrots. I’ll update this section once I have tracked it long enough.
What is the NPK of Carrots
The best fertilizer for carrots is an NPK with low nitrogen, a moderate amount of phosphorus, and high potassium.
Best Fertilizer for Carrots and Radishes
Although I’m currently experimenting with a homemade blend, so far the best fertilizer I’ve found for carrots and radishes is Big A Carrots which has an NPK of 1-9-3 and is organic.
Is 6-12-12 Fertilizer Good For Carrots
A 6-12-12 NPK fertilizer may be ok in lieu of compost before seeding your carrots. Mix it into the top two inches of soil. I do not recommend it after planting carrots because the nitrogen level can cause your carrots to fork and become hairy. And who wants to eat a hairy carrot?!?
