Celery, celeriac

One of the trying things about gardening is that it often takes months to find out whether you did things well — whether you actually learned what you needed to from your preceding failures, and whether that learning will finally translate into produce for your kitchen.

This is especially true for celery and its bulbar cousin celeriac, which are best sown for seedlings around mid to late January or the beginning of February. Over the years I’ve noticed that celery is one of the biggest stumbling blocks for many Eastern European gardeners, so here are my hard-earned lessons.

Raising the seedlings is tricky. Celery seed is extremely small, takes weeks to germinate, and only does so reliably in real warmth (25 °C and above). Throughout this time, the growing medium has to stay consistently moist. Celery has marshland ancestors and still demands marsh-like conditions if you don’t want it to become stressed. I sow into mini soil blocks, place them on a heat mat, and water daily. Old seed is not a problem in itself — I still use celery seed that’s six years old — but it does take longer to germinate, sometimes up to two weeks. At lower temperatures, germination rates drop sharply and become uneven.

I keep the plants in the mini blocks for one to two weeks, then pot them on into 5 cm soil blocks. From that point, I baby them on my planting bench for at least ten weeks, and they don’t mind even longer. Growth is slow at first, then somewhere around weeks eight to ten it suddenly accelerates — that’s the ideal planting-out stage. Because I plant them into beds with a very thick compost mulch (about 15 cm in my case), seedlings that are too small are impractical: mulch falls into the planting hole, or the plant can’t be set properly through the mulch, which leads to drying out. I always plant exactly at a drip emitter, because if celery dries out even once, it will bolt — and then you won’t get a proper bulb or thick stems.

Timing of planting out has to be just as exact. I only plant celery out together with the tomatoes — never earlier. Even a light frost can trigger bolting. Spacing is 30 × 30 cm. I know it looks generous, but it’s necessary.

About a month after planting out, I weed the bed once. After that, unless there’s something aggressive like nettles (which thrive on the amount of water celery receives), the mushroom-compost mulch and the celery’s rapidly expanding foliage suppress weeds well enough that there’s little else to do.

With a timer, I would run the drip irrigation for my garden for at least 15 minutes a day throughout the summer. In hot weather or during periods of atmospheric drought, maybe even 2 × 30 minutes per day. Always increase water quantity gradually, because celery thrives on stability. Sudden jumps in water supply lead to hollow hearts and cracking, which then invite rot.

From mid-summer onward, celeriac bulbs can already be lifted for soup. It’s worth harvesting every second plant early, so the remaining ones can size up properly. Around September, various fungi and bacteria that cause bulb rot become more active, so good airflow becomes critical. At that point it’s worth removing old, collapsed outer leaves — but celery still needs plenty of foliage. Stripping leaves does not make the bulb larger. What does is water and organic matter.

Stem celery differs mainly in culinary use and harvesting. It comes from varieties bred specifically for crisp stalks, with very little bulb formation. Because these plants don’t store energy in a bulb, everything goes into the foliage — which is why the stalks thicken and stay crunchy. (You can use celeriac stalks as celery too, but mostly for soups, as they’re far more fibrous.)

Stem celery can be harvested continuously: three to four outer stalks at a time can be removed without stressing the plant or triggering bolting. The tender inner heart is of course the best part, but if you remove it, the plant regenerates very slowly and usually bolts from the stress.

Stem celery tolerates cold fairly well, so I usually plant four or five plants into the polytunnel among the cucumbers. That way I can synchronize irrigation. Stem celery gets slightly less water than ideal there, but it copes well enough. Four to five plants already yield several kilos, so there’s little point in planting more. Still, in autumn and winter — when the tomato–pepper–cucumber trinity becomes deeply boring — I really appreciate having it.

Polytunnel-grown celery typically drops its leaves during harder frosts, but resprouts in spring and can be harvested until around March, before it bolts. That second wave often comes in handy, because by then the 30–40 celeriac bulbs I usually grow are already gone.