Top Of The Crops - Parsnip

Growing Parsnips in a Polytunnel

Parsnips require a big investment in terms of time and space but if you have a large enough polytunnel then you may like to grow some parsnips in it. Parsnips are a versatile vegetable that were once a staple like potatoes are now. 

Parsnips can be eaten mashed, roasted or boiled in a wide range of different recipes and though they have a strong flavour, can be delicious when cooked well and combined with the correct flavours.

Key Information

Parsnips are a root crop, or root vegetable, the roots of the plant Pastinaca sativa. Like carrots and parsley, their close relatives, they are members of the Apiaceae plant family. Modern varieties are all derived from the wild parsnip, native to Eurasia. 

Parsnips grow only relatively slowly. But get your gardening right and the delicious and healthy yields you can obtain can make the wait worthwhile. 

 
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The Preferred Conditions for Parsnips

To grow well, parsnips need:

  • A position in full sun. 

  • Fertile, light soil that drains freely and which is not stony or compacted. 

Provide the right growing conditions and you should find that parsnips are quite easy to grow, and will not need much of your time or attention. 

You can grow parsnips in the ground, in raised beds, or even in containers as long as you provide the right care. Raised beds can often be ideal for parsnips, especially if you have a heavier or stonier soil where you live. 

What you will need to grow Parsnips

To grow parsnips you will need:

  • Parsnip seeds.

  • A suitable growing location where you can provide the above preferred conditions. 

  • Facility to provide water for your crop when needed. 

  • Organic matter for mulching.

  • Fork or spade for harvesting the root crop. 

How to Grow Parsnips

Parsnips are not at all challenging to grow, though the seeds are often said to be tricky to germinate successfully. Follow the seed sowing instructions below and you are more likely to meet with success. 

Sowing Parsnip Seeds

Growing parsnips from seed worries some new gardeners because it is said that they can be difficult to get to germinate successfully. But if you choose the right location to sow your seeds, and get the timings right, you should have good results. 

Parsnip seeds need to be sown directly where they are to grow. They form tap roots and do not transplant very successfully. Germination rates can indeed be patchy if the seeds are sown too early – as it can be too cold for the seeds to sprout well. 

The right timings depend on precisely where you live. In the very mildest of regions, seeds might be sown as early as February but usually it is best to wait until at least mid-March, April or even May – especially in colder regions and further north. You should wait until the temperatures are around 12 degrees C. for best results. 

When sowing parsnip seeds you should sow into shallow drills around 1cm deep, sowing the seeds thinly along these drills. If you are making more than one row, these should be around 30cm apart. 

It is a good idea to mix in some radish seeds with your parsnip seeds to mark the rows and to make the most of the space. 

The radishes will germinate and appear far quicker than the parsnips, which will take around three weeks or even longer to appear. The radishes will mark your rows and will then be harvested before the slow growing parsnips need the space. 

Harvesting Parsnips

Parsnips will be ready to harvest when the foliage begins to die down in late summer or autumn. Do not try to pull the parsnips out by hand – ease them out of the ground gently using a fork. 

Before attempting to lift your parsnips you can get a quick look at the tops of the roots and feel for them in the soil or just above the soil surface. Mature parsnips will usually be around 5 - 7cm across at the top, at their widest part. 

Parsnips can also, however, be left in the soil until they are needed and the flavour will be best once the roots have experienced a light frost. Just mark your rows before the leaves die back entirely or you may struggle to find the roots when you later want to harvest them. 

Storing Parsnips

Parsnips will often be best left in the ground as mentioned above until they are needed. But where the ground freezes completely, you may wish to lift and store the roots after they have experienced a few light frosts. 

You can store undamaged roots of parsnips that are in good condition in a root cellar or other cool, dark location for several months. Like carrots and some other root crops, they are best stored in damp sand or potting mix or sawdust. 

If you do not have a suitable storage location where you live, you can also lift parsnips, slice, par-boil and freeze them, or use a pressure canner if you have one to preserve them in a range of recipes. 

Of course, there are also plenty of parsnip recipes you can use to use your harvest up right away. 

Care Tips for Parsnips

Parsnips are not challenging to care for,  but you do need to make sure, over time, that the crop's basic needs are met. Making sure that you eliminate additional competition due to overcrowding or weeds is very important, and of course you need to make sure that parsnips receive enough water especially through the summer months. 

Thinning Out Seedlings

Thin parsnip seedlings to a spacing of around 15cm when they are 2-3cm high. Take the weakest seedlings and leave the strongest in place to continue to grow. 

Weeding

Since parsnips are quite slow growing, it is important to keep on top of weeding, so that young parsnip plants don't have to compete for water, light and nutrients. Weed by hand, carefully, so that you do not accidentally damage the tops of the parsnip roots. 

Watering

Young parsnip plants need to be watered regularly until they become established, even outdoors. Of course, in a polytunnel you will be responsible for meeting all the water needs of your crop. If you are growing in containers remember that you will need to water more frequently than when growing in the ground. 

Mulching

Mulching around parsnip plants with organic matter, such as homemade compost or well-rotted manure will help to suppress weed growth to a degree, enrich and protect the soil, and conserve soil moisture. 

Pest Protection

Like carrots, parsnips can encounter issues with carrot fly. Where carrot fly is present, it is usually best to cover the crop from the start with insect-proof netting, which will prevent the carrot flies from laying their eggs around your parsnip crop. 

Varieties of Parsnips

When trying to decide which parsnips to grow, a good place to begin is with varieties that have received an award of garden merit (AGM) from the RHS. Currently, AGM Parsnips are:

  • ‘Albion’ 

  • ‘Gladiator’ 

  • ‘Pearl’ 

  • ‘Picador’

  • ‘Titan’ 

  • ‘Viper’ 

Another option is the well known traditional parsnip variety, 'Tender and True' which I have had success with in my own garden. 

Common Problems for Parsnips

When growing parsnips you will not typically encounter too many serious problems. However, things can of course go wrong if you get your timings wrong, especially if you sow the seeds outdoors too early. 

Issues can also arise if you have not chosen the right growing location and if the primary growing needs of the plants are not met. Roots can fork, for example, if the soil is too compacted or stony. Roots may split if you do not water enough during dry spells. 

Pests may occasionally also arise – most commonly carrot fly. This is why, as mentioned above, it can be a good idea to cover your crop from the very beginning with fine mesh netting, and to think about companion planting as an additional deterrent to these pests. 

Occasionally, you may encounter diseases too. Parsnip canker, for example, is an orange or brown rot that can affect the roots in dry conditions or overly fertile and rich soils or growing media. Some varieties are more resistant than others to this problem, such as 'Avonresister' and 'Archer' for instance, and the AGM option 'Albion' listed above. 

Top Tips for Growing Parsnips in a Polytunnel

Parsnips do not really need the protection of a polytunnel. But if you plan to leave the roots in the ground to harvest as needed over the winter months then a polytunnel will make the job of harvesting them easier and often a lot more pleasant too. 

Just make sure your parsnips have enough space and that you ventilate well through the summer. Of course, you also need to keep an eye on your plants and, most especially, make sure you are watering enough, and watering correctly when you need to provide all of the water your plants need. 

One other thing to think about when growing parsnips in your polytunnel is companion planting. For crop rotation purposes, it can be useful to grow parsnips alongside carrots and perhaps other root crops. 

But remember that carrots and parsnips share certain pests and other problems. So do celery, celeriac and parsley. So create polycultures with other beneficial plants between these family members to reduce the chances of any serious issues taking hold. 

Onions and other members of the onion family can be useful in this regard – in particular because they can help to confuse or distract carrot flies and may also help to repel other pest species.

Cooking Notes

Remember, parsnips certainly do not have to be boring. You can cook them in many different ways. Roasting, however, is a tried and tested favourite and is, in my opinion, the best way to enjoy the parsnips you have grown in your garden. Drizzled in olive oil and honey their sweetness will come to the fore.  

FAQs

What month do you plant parsnips?

Parsnips are direct sown sometime between March and May, varying based on local climate conditions.

What is the secret to growing parsnips?

The key to growing parsnips lies in proper timing, suitable soil depth, aeration, moisture, and weed management.

How do you know when parsnips are ready to harvest?

Mature parsnips are usually ready from early to mid-autumn when sown in spring, but they taste best after exposure to frosts.

How much space do parsnips need to grow?

Parsnips should be thinned to about 15cm between plants and 30cm between rows, although this is a general guideline.

Sources

O’Toole, P., (2023) Air fryer parsnips and carrots with chilli honey. BBC Food. [online] Available at: https://www.bbc.co.uk/food/recipes/air_fryer_parsnips_94114  

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