Traditionally parsnips are sown during the shortest days of the year and can still be harvested more than a year later. While they are not everybody's favourite vegetable, they are extremely hardy and can be left in the ground until required for use.
The parsnip, Pastinaca sativa, belongs to the Umbelliferae family, the same as carrots, celery and parsley. It makes sense to grow parsnips in fresh ground every year or after potatoes or cabbage or any crop that has been given a good dressing of organic manure.
Parsnips are deep rooted and if long parsnips are required, for the local show, for instance, then the soil must be deep and well drained. Deep digging is essential and while they like a good deal of humus, it should not be applied at the time of seed-sowing because fresh manure can cause forking. Avoid very dry sandy soils and stony soils which tend to produce forked and badly shaped roots.
The seed has to be sown early in the year, in fact much earlier than other crops and long before a good seedbed can be made under normal conditions. Quite often a brief spell of good weather allows a sowing to be made. If weather and soil conditions are suitable in January, then sow parsnip seed. February sowing is better than March, and April sowing is considered too late for a good crop, the roots staying small, but then that might be fine.
The seed is round and flat and is big enough to be handled individually. The life of the seed is short so always ensure that the seed packet is dated for the current year, otherwise germination might not take place. The seed is usually sown in groups of three of four at a spacings of ten to fifteen centimetres. The wider the spacing, the larger the roots will become.
Large-growing varieties like ‘The Student' and ‘Hollow Crown' will need more space to develop and the rows should be at least fifty centimetres apart. The seed may be sown ‘on the flat' or on top of drills. The big advantage of using drills especially on heavy or poorly-drained soils is that it helps drainage and helps to raise soil temperatures, encouraging early germination. The foliage of parsnips grows quite high and though the spacing may appear wasteful it is well worthwhile to give as much space as possible.
Parsnips need to be thinned out, or singled, at an early stage. Seedling parsnips emerge unevenly and irregularly. When sown on flat ground, it is sometimes difficult to identify the leaves of each seedling but as soon as they are big enough to handle - before the development of the first true leaf - they should be spaced to the distances recommended.
The older larger varieties are still preferred by many people but their great disadvantages are that they are very subject to parsnip canker which appears as a rust-coloured rot on the shoulder of the roots and causes severe wastage and damage on the roots later in the year. This is often aggravated by tiny mushroom fly grubs that gain access through the cankered parts.
The more modern varieties which are much smaller but more resistant to rust include, ‘Avonresister', ‘White Gem' and ‘Offenham', but this size is quite handy for home use. Early sown parsnips are usually ready for harvesting from August onwards. Main crops can be harvested right through the autumn and winter and a touch of frost is beneficial, sweetening and improving flavour. Parsnips can be harvested right into spring, even after the tops have sprouted again, but there is a cut-off point because the roots become tough and dry.
Parsnips are susceptible to the ravages of slugs and snails especially in the early spring as they are emerging. If damage is noticed, some control measures will ne necessary. Weeds can be a problem as the crop is slow to emerge and it is a good idea to put down a few quick germinating seeds like radish to mark the location of the rows especially if they are being sown on the flat. The only solution to the canker problem is to grow varieties that are resistant to it such as ‘Avonresister'.