It is a late winter/early spring plant to sow. Start them off indoors in February, so long as you can provide about 15°C of heat. You get funny germination – over the following fortnight you will have them coming through at different times.
From there, pop them into 8cm (3in) pots once they are easily handled. Be careful – and remember the mantra: “NEVER HANDLE THE STEMS, ONLY THE LEAVES”.
Use a pencil or a dibber to lever the plant from the ground, make a hole in the compost and use the same tool to lower the roots of the plant into their new home. Carefully firm in and then water lightly.
Keep the plants growing in their pots indoors until at least the end of May. In the last week, acclimatise your plants, so they get used to outdoor weather – but delay this for a week if the weather is cold. Simply stand the pots at the bottom of the greenhouse door during the day, and bring them in at night.
Plants that produce strong flavours or colours will need a lot of nutrients to manufacture these in the plant. Celeriac is no exception. Incorporate a lot of well-rotted manure into the soil. Their needs are simple: moisture and nutrients – but they must not be too wet. Add a little sand to heavy soils, and make it as crumbly as you can. Persistent hoeing before transplanting is important.
Plant out the seedlings – once the weather is right – at 30cm (12in) apart, and make the rows about 45cm (18in) apart. I find that two ten-foot rows are enough plants for me.
Maintain a regime of hoeing around the plants – they don’t like other plants touching their roots and you get a smaller crop.
Remove any side branches that appear, which just take nutrients away from the main growing roots.
During the summer, add more manure. Liberally sprinkle it around the area, keeping it off the plants, and lightly hoe it in.
Don’t let them become dry – especially in hot weather. But keep them from being waterlogged – this is a sure-fire way of encouraging rot. In really dry times, give them a mulch, so you can water less.
If a cold snap is forecast, cover them up. In the winter, once the crop is ready, and you want to keep them into spring, cover them with a cloche. It is a good idea to cover them with straw and a cloche together.
Large, firm roots with white flesh.
* ‘Prinz Celeriac’
Early production under cover.
A vigorous variety with good resistance to running to seed.
* ‘Giant Prague’
Stores well and has good flavour.
* ‘Ibis Celeriac’
Fast growing, with round roots that are easy to clean.
* ‘Snow White’
Really white – as you would expect.
Smaller roots, roundish, and easy to grow.
You can harvest from September. In August, remove the lower leaves and expose the roots somewhat. This allows the skins to harden and makes them better for storing.
Septoria isn’t good news when it comes to growing celeriac. Septoria apiicola is a leaf spot of celeriac and wild celery that destroys leaves, seeds and seedling roots. The knock-on effect is that crop yield is greatly reduced – sometimes down to nothing. It occurs all over the world, and the main way in which it is transmitted is on seed. Yes, the very seed you will be sowing in a few weeks time could already be infected with it. Think hygiene, and remove all traces of roots and leaves from the soil at harvest time. Think quality seed from reputable suppliers, and grow Septoria-tolerant varieties. ‘Prinz’ and ‘Ibis Celeriac’ are good varieties to grow.
They are fine in freezing weather once they have grown. You can keep them as described – covered in straw and a cloche. But they are better in a clamp. Dig a large hole and line it with at least 20cm (8in) of straw. Lay your clean roots on this and cover with another layer of straw, 20cm deep. Cover the lot with earth and remember to label it all so you know what is beneath that funny lump on the plot.