Carrots are not difficult to grow and come in all sorts of shapes, colours and sizes. The key to success when growing carrots in the polytunnel is to know what the soil conditions are in your space and to amend them as necessary, and to be aware of which varieties are the best ones to grow in certain areas and at certain times of year. Get in right and carrots could be a part of your home-grown diet for most of the year and can be pulled fresh from your polytunnel between around May and October, perhaps even longer if they are given a little extra protection.
Carrots are not particularly fussy about the fertility of the soil in which they are grown, but will not thrive in heavy clay, waterlogged soil or soil with too many stones. They are largely drought resistant and, once sown, will rarely need to be watered. If the foliage starts to wilt then you can water thoroughly every 10-14 days but this is not normally necessary in the UK. Carrots generally do best planted direct in the soil or in a raised bed, though it is also possible to grow them in small spaces and some varieties are short-rooted and ideal for small-scale container growing.
Carrots should be sown in shallow drills. They can be sown from early March (early varieties) to July or August for a crop to be protected with extra cloches or fleece from October. Since the seeds can take a while to germinate, it is a good idea to mark the rows with swifter to germinate and grow radish seeds. Just sow a few radish seeds at intervals along with the carrots. That way you will know where you can weed. Weeding is important as carrots abhor competition and can be crowded out if there are too many weeds around them. When the carrots are growing nicely you should thin them to around 7cm apart. The tiny carrots you thin can be washed and eaten in a salad.
Carrot flies are one of the biggest pest problems faced by carrots. These can be deterred by inter-planting carrots with onions and fragrant herbs, which mask the smell of the carrots. You can also take care not to crush the foliage when weeding and thinning. Growing in a raised bed could also help. If you live in an area where carrot fly is a big problem, however, you will probably want to consider a barrier or some form of protective cover, especially on earlier sowings.
If you give them the right growing conditions then you can harvest carrots right through the year, especially with a polytunnel and cloches to give an early or late crop extra protection. Mature carrots will be ready to harvest in 12-16 weeks from sowing, though earlier pullings can be used small for salads. Sow successionally every six weeks or so for a continual crop.
Very early crop – sow under cover in early March
Early crop – April
Maincrop – mid April to June
Lifting time – very early crop – June
Rest – July to October
For a November and December crop sow short rooted variety in August and cover with cloches from October.