Autumn is a good time to give your celeriac plants a little bit of TLC – they’ll benefit from a feed and a bit of a trim to help them reach a good size for you to harvest in winter time.
As celeriac plants begin to mature and the bulbs start to swell (which usually starts to happen in early autumn, so hopefully you will see some sign of swelling by now) you can remove some of the outer leaves. Pinch off any leaves that are shooting out of the side of the crown, or beginning to fall horizontal. You only need to leave 5 or 6 leaves growing from the crown. This will concentrate the plant’s energy into swelling the root rather than producing foliage. Over the next few weeks, just cut off any side shoots that appear.
A liquid feed now will boost the nutrients in the soil and help the celeriac grow. It’s also worth weeding well now as you don’t want your celeriac to be competing for the nutrients – too much competition equals small celeriac bulbs.
In terms of harvesting, we find that, like parsnips, celeriac roots are much tastier after a couple of frosts. And they usually need a little extra time to grow anyway. Once they reach a sensible size, let a couple of frosts sweeten them up and then harvest them whenever you want to use them.