The earliest crops are best, with Amsterdam-type cultivars that have narrow, cylindrical roots with smooth skins. These are delicious eased from the soil, swished under a tap and munched while holding on to the feathery foliage. They are also the most suitable to consider sowing between now and early spring - but only under glass, or at least cloches. Nantes types are generally bigger and can be grown both as early- and maincrop. Chantenay, berlicum and Autumn King types are all best for maincrops that you would expect to harvest in autumn, and can have the biggest roots. You can have carrots with round-ish roots, yellow carrots and every shade of orange. But all of them should have that sweetness and slightly musty aroma that you instantly absorb when you spull a baby carrot from the ground, but which seems to be almost totally lacking on the supermarket shelf.
Carrots do best in light, slightly alkaline soils that have not been freshly manured. They taste better in rather dry conditions, although a very dry spring will harm germination. I used to sow my carrots in rows and then thin them by hand to allow an inch or so between each seedling. But for the past few years I have broadcast them, simply scattering the seed over an entire square bed or in loose rectangles approximating to rows. These are never thinned except by random harvesting and seem to do just as well, without the same risk of attracting the dreaded carrot fly.
Carrot flies can apparently smell a carrot from half a mile away and are irresistibly drawn to it to lay their eggs. This does no harm. But when the maggots hatch they tunnel into the carrots. Early in the year this can make little difference to the crop, but by autumn it will encourage rot and can reduce each root by half. The answer is to prevent the fly from laying its eggs, by masking the scent with strong-smelling companion planting, such as chives, in and around the carrots - or simply by screening the fly off. The latter works well, either by pegging fleece over the growing carrots, lifting and replacing it when you harvest, or by putting up a 3ft (the flies keep low) screen around the bed. The fleece option is rather more practical.
- Amsterdam Forcing, small cylindrical roots but very early;
- Nantes 2, blunt ended, early and sweet.
- Chantenay, wedge-shaped, fast growing if sown into warm soil;
- Flyaway (F1), good all round carrot, especially raw and extra carrot fly resistance; Parisier Market 4, round-rooted carrot with good flavour.
Late, main-season varieties:
- Berlicum 2, long cylindrical root for harvesting September to Christmas;
- Rothild, stores very well and good for juicing;
- an Autumn King type with conical roots that keep well in the ground over winter.
Monty Don: Home truths | Life and style | The Observer