Days to germination: 14 to 20 days
Days to harvest: 100 to 120 days
Light requirements: Full sun
Water requirements: Frequent watering
Soil: Loose and fertile soil with extra fertilizer
Container: Possible in large pots
Definitely not a plant you see in many home gardens, but celeriac is a root vegetable worth trying if you are looking for something different. As the name may tell you, celeriac is related to celery but you are going to harvest the large round root rather than the leaves or stalks.
It’s sometimes called celery root or knob celery, and it does taste a bit like celery has the texture of a potato. The flesh of the root bulb is usually cooked for eating, but can be eaten raw. Like many other root vegetables, celeriac is high in fiber, as well as potassium, iron and vitamin C.
It takes a long time to grow, but also does poorly in hot weather. The best places to grow celeriac is in regions that don’t get excessive summer heat, which is typically in the north. The quickest to mature is the Diamant variety, which will be ready to eat in 100 days.
Starting from Seed
Because it can take so long to mature, it’s best if you start your seeds indoors at least 10 weeks before your expected frost date. Once your seeds have sprouted, keep your growing seedlings in a relatively cool area that still gets plenty of sun.
Your potting soil should be very loose, and you can just plant your seeds under a light layer of soil because the seeds need some light in order to germinate properly. You should sow more seed than you actually need as celeriac can be hard to sprout.
Start a few seeds in each seedling pot, and thin down to 1 plant per pot once they have started to grow.
Celeriac seedlings can be planted outside any time after your last frost date. Choose a spot that will get lots of sun, and add a heavy mix of fertilizer, manure or compost to the soil before you plant. Celeriac is considered to be a heavy-feeder and will require more nutrients in the soil than your average garden vegetable.
Your seedlings should be at least 8 inches from one another.
The roots of the celeriac are fragile and grow close to the surface of the soil, so you can’t do any heavy digging or cultivating around the plants. Weeds can be pulled by hand, or you can use mulch to smother them out more safely.
Not only is celeriac a heavy-feeder, it uses a lot of water as well. Water your plants regularly, every 2 or 3 days unless it’s been raining. In very hot weather, give them a drink every day.
As you see the bulb starting to form, snip away any extra side shoots and the lower leaves. When the cooler autumn weather arrives and the bulbs are getting larger, you can cover them up with soil or mulch to blanche them. Blocking out the sun will sweeten the flavor and lighten the roots. It’s not a necessity if you prefer not to take on the extra work. Most gardeners will keep their celeriac covered for 2 to 3 weeks before harvest time.
Celeriac can be grown in containers, but it’s large bulb and root system means you will need to have a large pot for each plant. You’ll need to be extra diligent with your plant care, with nearly daily watering and fertilizer treatments every 2 weeks to keep the potted plants healthy and productive.
Though they prefer lots of sun, celeriac doesn’t do well in the heat. So potted plants could be moved into the shade during the afternoon to help ease any heat stress.
Pests and Disease
Due to their close relation to the more common celery plants, celeriac is prone to the same insect pests and fungal diseases.
The biggest insect problem will be celery leaf miners, that chew small holes and tunnels in the plant’s leaves. They are quite small and will do minimal damage as long as you keep their numbers in check. Treat your plants with insecticide and pick off any leaves that have tunnels in them. The sprays aren’t very effective against the insects inside the leaves, so it’s best to take off the whole leaf if you can.
With all the water you’ll be giving to your celeriac plants, it’s no surprise that fungus blight can be a problem. Brown spots or blotches will start to form on the stalks and sometimes the leaves as well. If you treat with fungicide right away, you should be able to save your plants. Pick the effected leaves off if you can do so without killing the plant and then spray. If you also grow celery, don’t plant celeriac in the same area that had celery in previous years. The fungus overwinters in the soil and will be more of a threat if you don’t rotate your crops.
Harvest and Storage
The top part of the celeriac root will be visible above ground, so you can watch its size without having to dig it up. When the roots get to be around 3 inches across, you can harvest. Each plant will produce one root or bulb.
Depending on how your climate is, getting your harvest just after the first hard frost is ideal. The frost will really improve the taste of your celeriac, but after that it needs to be picked immediately. If you can’t get the timing just right, it’s not necessary to wait for the frost.
Celeriac is great for long-term storage if you have a cool dark place to keep it. Each root should last 2 or 3 months stored this way. It stores best if you leave it unwashed and unpeeled. Once you’ve peeled away the outer layer of the root, it should be stored in the fridge for a week or two, or you can also freeze it.