It should be no surprise that parsnips are closely related to carrots and also celery (including several familiar herbs such as fennel and parsley, as well as the toxic hogweed and hemlock) This group of plants were originally known as being in the Umbelliferous family (I imagine the flower head looking like an upside down umbrella) which has been renamed the Apiaceae family. All of these plants produce aromatic organic compounds (that is, they have distinctive aromas and flavours) Some like the parsnip and more especially the giant hogweed produce phototoxic substances which can sensitise the skin and in sunlight cause skin inflammation (contact with giant hogweed can cause severe burns)
And at this time of year (mid-March to early April) seeds from many of the cultivated plants in this family (that is, carrots, celery, fennel, parsley, angelica, anise, asafoetida, caraway, chervil, coriander, cumin, dill and lovage) can be sown. They have very similar growing conditions and pests including the Carrot fly (though as its name implies, carrots are more susceptible to this pest and others less so). Parsnip seeds do look slightly different from the others by having a paper wing round the seed. And they do tend to take a lot longer to germinate (at least 3 weeks in optimum conditions) but the seed also age quicker (that is, a large percentage of unused seed are unlikely to germinate the following year - many seasoned gardeners tend not to bother and buy fresh seed every year)
Sowing: ideally the seed should be sown where they are going to grow (to avoid disturbing the root - just like the carrot, if the seedling root is disturbed, it will not grow in the familiar shape but become twisted and possibly throw out multiple roots making food preparation difficult in the kitchen) However, at this time of year when the weather can oscillate from cold to mild to cold quite frequently, the change in temperature especially to cooler conditions, can impact how long it will take to germinate outdoors, and seeds end up being at risk of rotting in cold damp soil conditions. Just when you think they are never going to germinate or presume the slugs and snails have had a tasty meal, you sow a fresh row and that's when some of the earlier sowing then start to appear. It really is a waiting game with parsnips and then when the no-show is looking inevitable, wondering if you have left it too late to sow fresh. Early sowings are not necessary despite the seed sowing guide on seed packets - you can sow anytime during April and well into early May and the seed germination rate is much better in the warmer spring weather. Personally, my early indoor sowings usually ended up being oversized (the equivalent to 3-4 "normal sized" parsnips in one) by the time I'd dug some up in winter)
There are 2 things you can do which might give you an edge over outdoor sowing but be warned that both methods may disturb the root ... First, chitting! (Every time I type chitting, it sounds like "cheating", as in, having one over nature) You will need a lunch box or similar container with a lid and some paper towel. Fold the paper towel so that it is thick enough to absorb water and remain damp, and place it in the lunch box container. Add enough water to wet the paper, then tip the container to drain off excess water (we need it more damp than waterlogged) Now place your parsnip seeds on the surface of the paper - spread them apart so that if germination is earlier than expected, you may be able to rescue them before the roots have had time to entangle themselves with neighbouring seedlings. Place the lid on the container and put somewhere warm (preferably 10-12oC) Fresh seed is more likely to germinate earlier than older seed so do check for the first signs - as soon as the root appears, they need to be removed and planted.
Which takes you to tip no. 2. Obviously if you plant the seed and root directly into cold soil outside, the shock from the temperature difference is likely to kill the seedling off before it has had chance to complete the germination process. Parsnip seedlings produce a deep root long which can catch a lot of people out when sowing the seed in pots to plant out later - the roots are already dangling out the bottom of the pot before the first leaves appear. The cardboard inserts of toilet rolls (or even better, the much longer cardboard inserts of paper towel) make good temporary "plant pots" (though you will need to put paper or something to contain the compost inside the cardboard insert from falling out. It should be something which will later quickly rot and not prevent the root from growing beyond the length of the tube) Fill the tubes with compost, then gently tap the upright tube down so that the compost will compact down naturally (don't push it down with your fingers) Ideally you should have about a 1/4 inch depth from the top. Next water the compost in the tube so that it is damp (this will also compact the compost down - hopefully about a 1/2 inch from the top) Using a pair of tweezers, gently lift the germinating seed from the chitting container and place the seed with the emerging root on top of the compost and then fill the rest of the tube to the top with more compost. Trying to get the maximum amount of compost at this stage is key because it has a habit of compacting down later and this leaves even less growing room for the root. You might be better standing the tubes upright inside a deep tray (I often used empty ice cream tubs for this) and pack it so that the tubes don't fall over. Ideally the compost and water have been left at room temperature before sowing the seeds so that the germination is not interrupted by a sudden change in temperature.
In an ideal world, after germination is complete and the first true leaves appear, you should be hardening off the seedlings and planting out. In the real world, the root may already have gone beyond the length of the cardboard loo roll so keep an eye out and then plant the entire cardboard tube and contents into the bed. The cardboard will naturally rot down in the soil (don't worry about the mouldy patches appearing on the cardboard - they will have no effect on the seedling) and the plant will grow on. Try to bury the top of the cardboard under soil if possible (but avoid the seedling ending up below the soil level in the bed) - during hot sunny dry weather, the cardboard sticking out of the soil surface can start to act like a wick and draw moisture up from the soil. You can always tear the cardboard at the top while at the same time as planting (the cardboard should be soft from absorbing water from the compost and can be easily torn without disturbing the seedling)
When planting out, the recommendation is about 6 inches apart but the foliage can grow quite big so I preferred 8-9 inches apart, rows about a foot apart) I never used any Carrot Fly deterrent for my parsnips and don't recall having any problems - unlike carrots when foliage are damaged when thinning out or harvesting (releasing volatile aromatics into the air which attract the flies), parsnips stay in the ground until about late autumn (depending on whichever variety you have grown) I never bothered with harvesting parsnips until after the first frosts as this triggers a response in parsnips to convert starches to sugars (it is a strategy to prevent the roots from being damaged by freezing) which are so much nicer in whatever cooking method (I used to love parsnip chips, that is, thinly sliced / shavings and in the deep fat fryer though I can see the air fryer being a healthier alternative method ...)
Tender and True
are popular open pollinated varieties. I always grew White Gem because it was a shorter parsnip and wedged shaped, that is broad shoulders and tapered end which was ideal for my heavy clay soil. Long thin varieties are perhaps better for sandy soil - there's nothing like trying to dig out your parsnip from heavy clay soil in the middle of winter and you hear that audible crack and you are holding up half a parsnip in your hand. My first parsnip harvest tended to be on Christmas day (and I wasn't the only one daft enough to be on the allotment early digging up parsnips for the Christmas dinner) BUT, do watch the weather forecast and if it is a hard frost, it might be an idea to dig the parsnips up earlier. It can be quite an ordeal trying to dig your Christmas dinner from frozen ground and everyone at home is relying on you! Other popular varieties include
A lot of the F1 varieties tend to have varying levels of canker resistance. I can't say I had this problem but I did notice that the "shoulders" of the parsnip root that were proud of the soil surface tended to have some mild rot which rarely damaged the entire plant - on lifting up, I would cut it off and the rest of the root was fine. This kind of rot could be due to damage (being a bit too vigorous when hoeing the weeds, or maybe some pest or slug / snail trying to test the skin for weakness which then causes a wound for bacteria or fungus to enter) Parsnips can be left in the ground over winter and harvested as and when.
When new foliage appears in late winter / early spring, then it is time to lift up all the parsnips right away and take home to prepare them for freezing to use later - when leaves start growing, all the sweet sugars are being used up by the roots to grow so they won't taste as nice. If the parsnips are left in the ground in spring, all the energy stored in the roots will go to flower and seed production.