If you have seed you'd really like to use but are afraid they won't germinate at any sufficient ratio, there is a tactic you can try which works not only with parsnip but other veggies as well.
Place the seeds onto wet cotton balls, in a saucer or flat shallow container. Keep the seeds moist and warm and small white roots will appear on the viable seed. You now have pre-germinated seeds that you can sow. discard any that have failed.
Soil should be loosened to a depth of 2 feet, remove any rocks or other obstacles that would impede growth. In early spring, when soil temperature has reached at least 45 F, sow seeds 1/2 inch deep and 1 inch apart in rows that are 5-7 inches apart, this may vary ever so slightly from cultivar to cultivar so always consult the seed packet first.
I usually start mine indoors. Keep the seedbed uniformly moist. Parsnips generally take 2-3 weeks to germinate. Soil pH should be 5.5 to 7.0 for best results.
I like to sow some quick maturing "baby" carrots between my parsnip plants the carrot seed is sparsely planted between the parsnip seeds. The carrots will mature long before the parsnip has reached any significant size and will mark the row positions making cultivation / maintenance that much easier. Some gardeners do the same with radishes instead of carrots.
Avoid planting them near or in succession with Celery.
When your parsnip plants have reached 5-6 inches tall, thin them to roughly 3 inches apart. A layer of mulch around the plants is a good idea. For an optimal germination rate you should be using a fresh packet of seeds as the parsnip seed germination rate declines drastically after a year. Soak them in warm water overnight prior to planting.
Pests and Diseases
Parsnips don't have very many enemies within the insect realm, they do however experience some disease problems, the primary one being scabies and soft rot. Soft rot causes water-soaked spots on the leaves as well as roots. Carrot rust flies lay eggs near the crown of plants, and their larvae burrow into parsnip and carrot roots, causing rotting and reducing yields. If this is an issue cover your seedbed with a row cover to keep these pests away from your parsnip crop.
Proper cultural practices and good garden sanitation can generally avoid any of these issues
1.] Crop Rotation in your garden planting area
2.] Remove and destroy all plant refuse in the fall and use deep cultivation to bury any remaining refuse.
3.] Do not place diseased plants in the compost heap, as this will only serve to carry bacterial or fungal infestation into the next growing season.
4.] Avoid over watering . Use surface watering methods. Do not handle plants when the vines are wet.
5.] Weeds compete with vegetables for soil moisture and nutrients and also serve as hosts for insects and disease carrying bacteria and fungus. Control weeds in and around the garden .
6.] Control insect pests such as aphids, which are known to transmit diseases from plant to plant.
7.] Use or to reduce disease and blossom-end rot problems.
8.] Choose a sunny location for your tomatoes. Leaf disease problems are much less likely to occur in a sunny location than in a shady one.
9.] Apply recommended fungicides according to label directions at the first sign of leaf spot diseases
10.] Remove abnormal or unhealthy appearing plants as soon as they are observed. To reduce the spread of suspected diseases wash hands and tools with a mild detergent after handling suspect plants.
Aphids, Leaf Miners, Carrot RustFlies do on occasion make their presence known in parsnips plantings. See individual guides to these insects.
Parsnips are generally ready to harvest in about 120 days, however the roots taste sweeter if they're left in the ground until after the first frost. Parsnips can be kept in the ground over the winter season by covering them with layer of mulch roughly 2-inches thick. Harvesting the parsnip roots throughout the winter and subsequent spring as needed. You should however, harvest all previous seasons parsnips before your new crop begins.