The toughest part of growing carrots, I believe, is germinating the seed. The biggest thing to remember is that carrot seed doesn’t germinate well in soils that are too warm so they are best sown in the spring and early summer before the temps are too hot.
I sow mine in wide bands and blocks rather than single rows. For instance, in a 4×4 ft block, I would plant a row every 6 inches with seeds spaced about 1/4″ within that row. If I was only planting a single “row” of carrots, I would plant 3 rows, 6″ apart so that my total carrot row is one foot wide.
Sowing my seeds 1/4 inch apart gives me some flexibility. Once they’ve germinated, I thin those seedlings to 1″ apart. Then I leave them until baby carrots have reached a size that I feel is worth pulling. I’ll then harvest every other one, pulling the largest ones, and leaving the rest to grow on into larger carrots. I will repeat this process again once those carrots have sized up, pulling every other one and leaving the rest to form large storage carrots for winter. You now have the benefit of 3 harvests instead of just one!
Keep your carrots weed free. Weeding a few times in the beginning will pay off. Once the carrots have begun to fill the space, weed pressure should be gone.
Tips for germination. Be sure you keep your carrot row moist while you wait for them to germinate. If a crust forms on the top of your soil, the seedlings will have a hard time pushing through. If you plant during hot weather, shading the carrot seedlings by placing a board over the top, raised on bricks, will help the soil to stay cooler. Take extra care to keep the soil moist.
I plant carrots all the way through the end of July. Those later plantings are often the sweetest carrots as they are harvested in the cool of the fall.