We have sown our carrots and leeks this weekend, and decided to attempt companion planting to avert carrot-fly. Three rows of leeks ‘flank’ the two rows of carrots, which we hope will throw at least some of them off the scent.
We prepared the bed by working the soil well, down about a bit over a spades’ depth, followed by a layer of basic compost on top to provide the fine-tilth required. Using the short side of a paving stone, we created long shallow drills.
Carrot-flies are particularly attracted to the smell of the carrot leaves being crushed during thinning, so best to avoid this by sowing thinly. After sowing we lightly covered the seeds, watered with a fine rose and gently firmed down the earth. As carrot-flies like to find a nice protected hole in which to lay their destructive brood, it is apparently best to flatten the earth as much as possible without over-compacting the earth.
Carrot-flies are vertically challenged in that they only move horizontally, so we will be adding some sort of foot-high barrier around the bed as well. Here’s to hoping the carrots don’t come up bifurcated.