Carrots: why do they need to be thinned after sowing?

Thinning carrots, as with spinach or turnips, is one of those thankless garden chores that, while necessary, isn't much fun. But why is it necessary to thin carrot seedlings?

Preparation before sowing

Carrots grow best in a sunny spot with deep, well-drained soil and no clods. Of course, we don't all have perfect soil, and in this respect, raised bed planting can then be a good solution. If your soil is shallow or heavy, you can opt for compact carrot varieties such as Chantenay with red flesh and short, thick roots. Or smaller varieties like Little Finger, which have thin roots 10 cm long.

As soon as you've chosen a good location for your crop, it's time to amend the soil. If using manure, make sure it is at least two years old. This is because too high a concentration of nitrogen in partially composted manure can cause the roots of carrots to branch out or become covered in hairs.

Sowing and thinning

Sow carrot seeds directly into the garden in mid-spring, about a week or two before the last expected spring frost. You can access the sowing calendar for carrots here. If you have a cold frame or tunnel greenhouse, you can sow up to two months earlier. To sow the seeds, make a furrow in the ground about a centimetre deep. Generally, you dig the furrow with your finger or apply the tip of the garden fork to the surface of the soil, exerting gentle pressure.

This operation gives you an initial opportunity to minimise the need to thin the carrots later on. How? By sowing just two to three seeds per centimetre and spacing them as far apart as possible. Cover the seeds with a thin layer of soil or horticultural vermiculite and water the soil carefully with a light spray. It is necessary to keep the soil constantly moist during seed germination, which can take from 14 to 21 days, sometimes longer.

To ensure an optimum, quality carrot production season, it is advisable to sow successively every four to six weeks, from mid-spring to mid-summer. The last carrot sowings take place at the end of July and the carrots are harvested throughout the autumn and winter.

Why thin out carrot seedlings

Now we come to the fateful question: why thin out your carrot seedlings? Well, for the simple reason that they are very small and it's easy for them to be inadvertently sown too densely. When they are too close together, there is not enough room for healthy roots to develop, and the roots risk looking stunted or misshapen. They should therefore be removed to give them enough room to develop. In general, one plant is left every 5 to 10 centimetres. I talk more about the thinning technique in this article.

Sowing coated carrot seeds

One of the easiest ways to space carrot seeds properly and limit thinning is to use coated seeds. Pelleted seeds are coated with an inert clay thanks to which all the seeds are the same size and shape. This is a natural substance that has the advantage of not being harmful to the environment. This method is suitable for market gardeners and farmers who use sowing equipment. But it's also ideal for gardeners who find large seeds easier to handle and plant. Space the coated seeds two centimetres apart. Ensure sufficient humidity until the seeds germinate and grow properly.