Home grown carrots are a delight but they are difficult to keep clean of the menace that is carrot fly and I must be honest and say that it is hard to grow good carrots organically without keeping the whole crop covered all the time with a white shroud of fleece or enviromesh. If you don’t mind the crop being covered for the 12 weeks that it takes carrots to grow then this is by far your best bet for a clean crop.
I have found that it is the carrots sown from mid summer onwards that are the worst affected and these are the crops that I cover. Despite what the books say about all the various treatments and techniques to avoid the pesky fly, the best way is to cover them. You may read about barriers and expensive nematodes as biological controls, about growing them with allium crops and not having other plants in the same family like celery and parsnips around. They are all true and good to know about, but covering remains favourite for late season crops, always.
So I only grow the short season early carrots like Amsterdam Forcing, or Nantes and sometimes the little round Paris Market or Parmex. These taste so good that I don’t bother growing main crop carrots because they are cheap to buy and not nearly as tasty as the smaller types.
You can grow them well in containers but you will need to pay much more attention to thinning them out because there is less room. I never thin out in the beds because the smell of the crushed foliage is what attracts the fly. And I prefer thin, delicate baby carrots in any case.
Carrots don’t do great in very rich soil. In an old fashioned rotation such as the one we used to run in the kitchen gardens at The Lost Gardens of Heligan, carrots came in year 2. Year one saw the soil being trench dug, lots of manure thrown in the trench and then potatoes grown on that patch followed by winter brassicas that were planted after the potatoes had been harvested.
By the time year 2 had arrived all the bulky organic matter had been gobbled up by the spuds and the brassicas, leaving the soil rich but not overly so, most of the nutrients gone and just the right amount left to grow a carrot.
The key to success here is to sow when the soil has warmed up. Plants in this family (apiaceae) that include celery, parsley and parsnips, do not like cold soil and they can be tricky about germinating. Wait for a nice warm day in April when you can put your hand on to the soil and feel the warmth coming off it. That is the moment to sow carrots outside.
The seed drill must be no deeper than 2cm. Don’t bury carrot seed, they’ll never find their ay up poor things. The seed is small! Cover over and firm in with your hand. Don’t water. Let the rain do the work unless you are growing in pots in which case you must water.
Covering the crop.
The best time to do this is immediately after sowing the seed. When the seeds germinate and the foliage starts to grow it will push the fleece up but if you are using enviromesh you may need to support it off the crop as it is that bit heavier than fleece. This you can do by driving a cane into the soil and putting a bottle or jam jar over the top to stop the stick puncturing the fleece.
You will know when your carrots are ready because when you push the soil away from the green leaves it will reveal a carrot. Nothing more complicated than that.
Nothing more to say. Even about varieties. You can use carrot fly resistant varieties. Breeding has improved resistance these days but the carrots are not as tasty and even less reliable growers.