If you wish to grow parsnips it is important to plant the seeds in moist soil that is free from stones and is slightly alkaline. Parsnips are usually sown early in the growing season, as soon as the ground has warmed up enough to work the soil. Parsnip seeds are planted in rows, with holes around 1 inch (about 2.5 cm) deep and about 15 inches (around 38 cm) apart. You should plant a few seeds in each hole and only keep the strongest seedling from each group. Parsnips are usually picked right at the end of the growing season but can be left in the ground over the winter months.
It is not advisable to grow parsnips in vegetable gardens where the earth is too thin or stony, as the roots will not develop properly. The soil needs to be deep enough to accommodate the fully grown parsnip. For smaller parsnips, a hole 1 inch (about 2.5 cm) deep for the seeds will be adequate, but, if you are planting parsnips that are of a larger, longer variety, it might be necessary to use a long tool such as a crowbar to make deeper holes. These holes should be around 1 foot (about 30 cm) deep and 3 feet (around 91 cm) apart, with a diameter of about 8 inches (approximately 20 cm). Each hole is filled with potting soil before sowing the parsnip seeds.
Some gardeners recommend that, when growing parsnips, you should plant lettuces between the parsnip seeds. As lettuces grow more quickly than parsnips, they can be a useful marker of the parsnip rows and may be picked and eaten before the parsnips require the space they occupy. Other markers, such as twigs, could be used instead.
If you grow parsnips, they should not need any attention after they have become established, apart from keeping the soil free from weeds. Occasionally, wet weather can lead to parsnips being affected by canker. The roots crack and are vulnerable to being invaded by fungi, which cause rotting. Sowing parsnips later may help reduce the risk of canker.
When harvesting parsnips, the longer varieties can be difficult to ease out of the ground with a fork. In this case, you could try digging a deep hole beside each parsnip through which you may remove the roots. Once they are detached from their roots, it should be easier to harvest the parsnips. Each hole you make can be filled with soil from the next one as you move along the row. People who grow parsnips should be aware that roasting them produces a much tastier result than boiling.