Carrots are sown directly where they are to grow in rows 15 cm apart and thinned as the roots develop to 2.5cm between the plants - the thinnings can be eaten. Plant in ground which was manured in a previous year as a high content of organic material can cause forked and twisted roots, as will stones and a shallow bed. To avoid root flies cover with horticultural fleece as soon as they begin to grow and keep it there until the crop is harvested - a very fine mesh material such as Enviromesh is more robust alternative. Arrange it over hoops and anchor it in the soil so there are no gaps. Try to sow as thinly as possible to reduce the amount of thinning, as the smell of crushed foliage attracts the root flies. Inter cropping with onions or garlic is said to mask the carrot odour from the flies. Sow at 4 to 6 week intervals for a succession of crops. Irregular watering can cause the developing roots to burst if a large amount is applied after a period of drought.
They are usually harvested when the top of the root is about 2.5cm in diameter.
Parsnips are grown in a similar way as for carrots, but the rows should be 30 cm apart and thin to 15 cm between plants. Fresh manure, acid conditions and irregular watering can lead to Canker, the main disease of parsnips for which there is no chemical treatment. Root flies are not as big a problem as they are for carrots, but they can also attack parsnips, so give them similar protection.
Harvest when the foliage dies down, usually in October. The flavour is made sweeter if they are frosted, and they are usually lifted from the ground when required. If there are soil pests around they can be lifted and stored in damp sand or in a clamp.