Daucus carota Full Sun USDA Zones 4 -10
Carrots grow well in containers, they do best in cooler temperatures as opposed to the balmy hot summer weather. They are a hardy crop that should be planted in early spring.
Prolonged temperatures below 50 degrees F tend to make the roots longer, more slender and paler in color than expected. The best temperature for the highest quality roots is between 60 and 70 degrees F.
Good drainage holes should be in every pot you plant in are essential. Pot Size: Size Matters - The more growing room the root system has, the better the carrot roots will develop. Your pot should be big enough to accommodate the anticipated length of the carrot with at least a half foot of room to spare. A container can never be too big, but it can certainly be too small leading to distorted poorly formed, fibrous and woody carrots.
If at all possible try not to use soil from your yard, especially if you are going to bring your plants inside. Potting soil with some vermiculite and or perlite is best. If you are going to use ground soil - it will work - but potting soil is best.
Fertilizer in containers will wash out, where as in the ground - it is retained in the soil much longer. With container plants, smaller, but consistent doses of soluble fertilizer with their watering is advisable.
Fertilize with a water soluble fertilizer every 7 - 10 days, a lower dose than you would give plants in the garden because you will be fertilizing more frequently. Do not use a fertilizer that is high in nitrogen as this will lead to a lush foliage and poor root development. Carrots need lots of potassium, incorporating some wood ash into the soil will help. They also need phosphorus, Some nitrogen is necessary, but too much is not good.
Compost added to the containers is a good idea for outdoor plants. Some people use worm castings, if you have access to these - go for it. See Worm Composting.
Carrots require larger amounts of water than many other popular edible garden vegetables, they are not tolerant of drought or prolonged hot weather - especially in their later stages.
In hot summer weather pots heat up significantly quicker than ground soil, so keeping them well watered and mulched to retain moisture is a must.
Mulch on the soils surface, such as wood chips or decorative bark is not only aesthetically appealing inside or outside it is beneficial to the health of your plants.
Trays under the pots are used for house plants to catch excessive water, they aren't necessary with tomato or other outdoor plants. The trays will hold too much moisture at the base of the roots, for too long and could easily lead to root rot.
Make Sure Your Plants are located where they can get adequate light. Carrots will tolerate partial shade but thrive in full sun, 6 - 8 hours daily. During hot weather it is advisable to move them to a shadier location to avoid the excessive heat they do not fare well in.